diff --git a/src/main/java/org/codelibs/fess/api/json/JsonApiManager.java b/src/main/java/org/codelibs/fess/api/json/JsonApiManager.java
index 8c0b11ab6..36936d3a9 100644
--- a/src/main/java/org/codelibs/fess/api/json/JsonApiManager.java
+++ b/src/main/java/org/codelibs/fess/api/json/JsonApiManager.java
@@ -177,7 +177,7 @@ public class JsonApiManager extends BaseJsonApiManager {
             }, OptionalThing.empty());
             response.flushBuffer();
             if (logger.isDebugEnabled()) {
-                logger.debug("Loaded " + count + " docs");
+                logger.debug("Loaded {} docs", count);
             }
         } catch (final Exception e) {
             final int status = 9;
diff --git a/src/main/java/org/codelibs/fess/app/job/AllJobScheduler.java b/src/main/java/org/codelibs/fess/app/job/AllJobScheduler.java
index e15e80b8d..64f214274 100644
--- a/src/main/java/org/codelibs/fess/app/job/AllJobScheduler.java
+++ b/src/main/java/org/codelibs/fess/app/job/AllJobScheduler.java
@@ -79,12 +79,12 @@ public class AllJobScheduler implements LaJobScheduler {
 
         TimeoutManager.getInstance().addTimeoutTarget(() -> {
             if (logger.isDebugEnabled()) {
-                logger.debug("Updating scheduled jobs. time:" + schedulerTime);
+                logger.debug("Updating scheduled jobs. time:{}", schedulerTime);
             }
             final long now = System.currentTimeMillis();
             scheduledJobService.getScheduledJobListAfter(schedulerTime).forEach(scheduledJob -> {
                 if (logger.isDebugEnabled()) {
-                    logger.debug("Updating job schedule:" + scheduledJob.getName());
+                    logger.debug("Updating job schedule:{}", scheduledJob.getName());
                 }
                 try {
                     jobHelper.register(scheduledJob);
diff --git a/src/main/java/org/codelibs/fess/app/job/ScriptExecutorJob.java b/src/main/java/org/codelibs/fess/app/job/ScriptExecutorJob.java
index a64f1727d..bceebb3cf 100644
--- a/src/main/java/org/codelibs/fess/app/job/ScriptExecutorJob.java
+++ b/src/main/java/org/codelibs/fess/app/job/ScriptExecutorJob.java
@@ -70,7 +70,7 @@ public class ScriptExecutorJob implements LaJob {
 
         if (!jobManager.findJobByUniqueOf(LaJobUnique.of(id)).isPresent()) {
             if (logger.isDebugEnabled()) {
-                logger.debug("Job " + id + " is running.");
+                logger.debug("Job {} is running.", id);
             }
             return;
         }
@@ -83,7 +83,7 @@ public class ScriptExecutorJob implements LaJob {
             }
 
             if (logger.isDebugEnabled()) {
-                logger.debug("Starting Job " + id + ". scriptType: " + scriptType + ", script: " + script);
+                logger.debug("Starting Job {}. scriptType: {}, script: {}" , id, scriptType, script);
             } else if (scheduledJob.isLoggingEnabled() && logger.isInfoEnabled()) {
                 logger.info("Starting Job " + id + ".");
             }
@@ -114,7 +114,7 @@ public class ScriptExecutorJob implements LaJob {
             }
             jobLog.setEndTime(ComponentUtil.getSystemHelper().getCurrentTimeAsLong());
             if (logger.isDebugEnabled()) {
-                logger.debug("jobLog: " + jobLog);
+                logger.debug("jobLog: {}", jobLog);
             }
             if (scheduledJob.isLoggingEnabled()) {
                 jobHelper.store(jobLog);
diff --git a/src/main/java/org/codelibs/fess/app/service/SearchLogService.java b/src/main/java/org/codelibs/fess/app/service/SearchLogService.java
index 722c2043b..926852ec9 100644
--- a/src/main/java/org/codelibs/fess/app/service/SearchLogService.java
+++ b/src/main/java/org/codelibs/fess/app/service/SearchLogService.java
@@ -386,7 +386,7 @@ public class SearchLogService {
                 }
             } catch (final Exception e) {
                 if (logger.isDebugEnabled()) {
-                    logger.debug("Failed to parse " + pager.requestedTimeRange, e);
+                    logger.debug("Failed to parse {}", pager.requestedTimeRange, e);
                 }
             }
         }
@@ -411,7 +411,7 @@ public class SearchLogService {
                 }
             } catch (final Exception e) {
                 if (logger.isDebugEnabled()) {
-                    logger.debug("Failed to parse " + pager.requestedTimeRange, e);
+                    logger.debug("Failed to parse {}", pager.requestedTimeRange, e);
                 }
             }
         }
@@ -433,7 +433,7 @@ public class SearchLogService {
                 }
             } catch (final Exception e) {
                 if (logger.isDebugEnabled()) {
-                    logger.debug("Failed to parse " + pager.requestedTimeRange, e);
+                    logger.debug("Failed to parse {}", pager.requestedTimeRange, e);
                 }
             }
         }
@@ -458,7 +458,7 @@ public class SearchLogService {
                 }
             } catch (final Exception e) {
                 if (logger.isDebugEnabled()) {
-                    logger.debug("Failed to parse " + pager.requestedTimeRange, e);
+                    logger.debug("Failed to parse {}", pager.requestedTimeRange, e);
                 }
             }
         }
diff --git a/src/main/java/org/codelibs/fess/app/web/admin/backup/AdminBackupAction.java b/src/main/java/org/codelibs/fess/app/web/admin/backup/AdminBackupAction.java
index 431944421..5af92176f 100644
--- a/src/main/java/org/codelibs/fess/app/web/admin/backup/AdminBackupAction.java
+++ b/src/main/java/org/codelibs/fess/app/web/admin/backup/AdminBackupAction.java
@@ -278,7 +278,7 @@ public class AdminBackupAction extends FessAdminAction {
             });
         } catch (final Exception e) {
             if (logger.isDebugEnabled()) {
-                logger.debug("Failed to parse " + line, e);
+                logger.debug("Failed to parse {}", line, e);
             }
             return null;
         }
diff --git a/src/main/java/org/codelibs/fess/app/web/admin/maintenance/AdminMaintenanceAction.java b/src/main/java/org/codelibs/fess/app/web/admin/maintenance/AdminMaintenanceAction.java
index 13bee73d9..bb6e34abe 100644
--- a/src/main/java/org/codelibs/fess/app/web/admin/maintenance/AdminMaintenanceAction.java
+++ b/src/main/java/org/codelibs/fess/app/web/admin/maintenance/AdminMaintenanceAction.java
@@ -251,7 +251,7 @@ public class AdminMaintenanceAction extends FessAdminAction {
                         zos.putNextEntry(entry);
                         final long len = Files.copy(filePath, zos);
                         if (logger.isDebugEnabled()) {
-                            logger.debug(filePath.getFileName() + ": " + len);
+                            logger.debug("{}: {}", filePath.getFileName(), len);
                         }
                     } catch (final IOException e) {
                         logger.warn("Failed to access " + filePath, e);
diff --git a/src/main/java/org/codelibs/fess/app/web/admin/plugin/AdminPluginAction.java b/src/main/java/org/codelibs/fess/app/web/admin/plugin/AdminPluginAction.java
index 6163a79d3..5f23d1b5b 100644
--- a/src/main/java/org/codelibs/fess/app/web/admin/plugin/AdminPluginAction.java
+++ b/src/main/java/org/codelibs/fess/app/web/admin/plugin/AdminPluginAction.java
@@ -87,7 +87,7 @@ public class AdminPluginAction extends FessAdminAction {
                 if (tempFile.exists() && !tempFile.delete()) {
                     logger.warn("Failed to delete {}.", tempFile.getAbsolutePath());
                 }
-                logger.debug("Failed to copy " + filename, e);
+                logger.debug("Failed to copy {}", filename, e);
                 throwValidationError(messages -> messages.addErrorsFailedToInstallPlugin(GLOBAL, filename), () -> asListHtml());
             }
             new Thread(() -> {
diff --git a/src/main/java/org/codelibs/fess/app/web/go/GoAction.java b/src/main/java/org/codelibs/fess/app/web/go/GoAction.java
index 1ef415ccd..1e6b6189e 100644
--- a/src/main/java/org/codelibs/fess/app/web/go/GoAction.java
+++ b/src/main/java/org/codelibs/fess/app/web/go/GoAction.java
@@ -134,7 +134,7 @@ public class GoAction extends FessSearchAction {
                 try {
                     final StreamResponse response = viewHelper.asContentResponse(doc);
                     if (response.getHttpStatus().orElse(200) == 404) {
-                        logger.debug("Not found: " + targetUrl);
+                        logger.debug("Not found: {}", targetUrl);
                         saveError(messages -> messages.addErrorsNotFoundOnFileSystem(GLOBAL, targetUrl));
                         return redirect(ErrorAction.class);
                     }
diff --git a/src/main/java/org/codelibs/fess/crawler/FessCrawlerThread.java b/src/main/java/org/codelibs/fess/crawler/FessCrawlerThread.java
index 0bd4c5568..6774f680f 100644
--- a/src/main/java/org/codelibs/fess/crawler/FessCrawlerThread.java
+++ b/src/main/java/org/codelibs/fess/crawler/FessCrawlerThread.java
@@ -96,7 +96,7 @@ public class FessCrawlerThread extends CrawlerThread {
                 final String id = crawlingInfoHelper.generateId(dataMap);
 
                 if (logger.isDebugEnabled()) {
-                    logger.debug("Searching indexed document: " + id);
+                    logger.debug("Searching indexed document: {}", id);
                 }
                 final Map<String, Object> document =
                         indexingHelper.getDocument(
@@ -115,7 +115,7 @@ public class FessCrawlerThread extends CrawlerThread {
                 if (expires != null && expires.getTime() < System.currentTimeMillis()) {
                     final Object idValue = document.get(fessConfig.getIndexFieldId());
                     if (idValue != null && !indexingHelper.deleteDocument(fessEsClient, idValue.toString())) {
-                        logger.debug("Failed to delete expired document: " + url);
+                        logger.debug("Failed to delete expired document: {}", url);
                     }
                     return true;
                 }
@@ -137,12 +137,12 @@ public class FessCrawlerThread extends CrawlerThread {
 
                 final int httpStatusCode = responseData.getHttpStatusCode();
                 if (logger.isDebugEnabled()) {
-                    logger.debug("Accessing document: " + url + ", status: " + httpStatusCode);
+                    logger.debug("Accessing document: {}, status: {}", url, httpStatusCode);
                 }
                 if (httpStatusCode == 404) {
                     storeChildUrlsToQueue(urlQueue, getAnchorSet(document.get(fessConfig.getIndexFieldAnchor())));
                     if (!indexingHelper.deleteDocument(fessEsClient, id)) {
-                        logger.debug("Failed to delete 404 document: " + url);
+                        logger.debug("Failed to delete 404 document: {}", url);
                     }
                     return false;
                 } else if (responseData.getLastModified() == null) {
@@ -162,7 +162,7 @@ public class FessCrawlerThread extends CrawlerThread {
                     final Date documentExpires = crawlingInfoHelper.getDocumentExpires(crawlingConfig);
                     if (documentExpires != null
                             && !indexingHelper.updateDocument(fessEsClient, id, fessConfig.getIndexFieldExpires(), documentExpires)) {
-                        logger.debug("Failed to update " + fessConfig.getIndexFieldExpires() + " at " + url);
+                        logger.debug("Failed to update {} at {}", fessConfig.getIndexFieldExpires(), url);
                     }
 
                     return false;
@@ -223,7 +223,7 @@ public class FessCrawlerThread extends CrawlerThread {
             return null;
         }
         if (logger.isDebugEnabled()) {
-            logger.debug("Found documents: " + docList);
+            logger.debug("Found documents: {}", docList);
         }
         final Set<RequestData> urlSet = new HashSet<>(docList.size());
         for (final Map<String, Object> doc : docList) {
diff --git a/src/main/java/org/codelibs/fess/crawler/transformer/FessFileTransformer.java b/src/main/java/org/codelibs/fess/crawler/transformer/FessFileTransformer.java
index 5caa2fb62..3b8204689 100644
--- a/src/main/java/org/codelibs/fess/crawler/transformer/FessFileTransformer.java
+++ b/src/main/java/org/codelibs/fess/crawler/transformer/FessFileTransformer.java
@@ -32,7 +32,7 @@ public class FessFileTransformer extends AbstractFessFileTransformer {
     @PostConstruct
     public void init() {
         if (logger.isDebugEnabled()) {
-            logger.debug("Initialize " + this.getClass().getSimpleName());
+            logger.debug("Initialize {}", this.getClass().getSimpleName());
         }
         fessConfig = ComponentUtil.getFessConfig();
     }
@@ -55,7 +55,7 @@ public class FessFileTransformer extends AbstractFessFileTransformer {
         }
         final Extractor extractor = extractorFactory.getExtractor(responseData.getMimeType());
         if (logger.isDebugEnabled()) {
-            logger.debug("url=" + responseData.getUrl() + ", extractor=" + extractor);
+            logger.debug("url={}, extractor={}", responseData.getUrl(), extractor);
         }
         return extractor;
     }
diff --git a/src/main/java/org/codelibs/fess/crawler/transformer/FessStandardTransformer.java b/src/main/java/org/codelibs/fess/crawler/transformer/FessStandardTransformer.java
index 1e1cf2e0a..897ed1e0b 100644
--- a/src/main/java/org/codelibs/fess/crawler/transformer/FessStandardTransformer.java
+++ b/src/main/java/org/codelibs/fess/crawler/transformer/FessStandardTransformer.java
@@ -32,7 +32,7 @@ public class FessStandardTransformer extends AbstractFessFileTransformer {
     @PostConstruct
     public void init() {
         if (logger.isDebugEnabled()) {
-            logger.debug("Initialize " + this.getClass().getSimpleName());
+            logger.debug("Initialize {}", this.getClass().getSimpleName());
         }
         fessConfig = ComponentUtil.getFessConfig();
     }
@@ -62,7 +62,7 @@ public class FessStandardTransformer extends AbstractFessFileTransformer {
         }
 
         if (logger.isDebugEnabled()) {
-            logger.debug("url=" + responseData.getUrl() + ", extractor=" + extractor);
+            logger.debug("url={}, extractor={}", responseData.getUrl(), extractor);
         }
         return extractor;
     }
diff --git a/src/main/java/org/codelibs/fess/crawler/transformer/FessXpathTransformer.java b/src/main/java/org/codelibs/fess/crawler/transformer/FessXpathTransformer.java
index d90468d7d..f7e624744 100644
--- a/src/main/java/org/codelibs/fess/crawler/transformer/FessXpathTransformer.java
+++ b/src/main/java/org/codelibs/fess/crawler/transformer/FessXpathTransformer.java
@@ -109,7 +109,7 @@ public class FessXpathTransformer extends XpathTransformer implements FessTransf
     @PostConstruct
     public void init() {
         if (logger.isDebugEnabled()) {
-            logger.debug("Initialize " + this.getClass().getSimpleName());
+            logger.debug("Initialize {}", this.getClass().getSimpleName());
         }
         fessConfig = ComponentUtil.getFessConfig();
     }
@@ -331,7 +331,7 @@ public class FessXpathTransformer extends XpathTransformer implements FessTransf
     protected boolean isValidCanonicalUrl(final String url, final String canonicalUrl) {
         if (url.startsWith("https:") && canonicalUrl.startsWith("http:")) {
             if (logger.isDebugEnabled()) {
-                logger.debug("Invalid Canonical Url(https->http): " + url + " -> " + canonicalUrl);
+                logger.debug("Invalid Canonical Url(https->http): {} -> {}", url, canonicalUrl);
             }
             return false;
         }
@@ -786,16 +786,16 @@ public class FessXpathTransformer extends XpathTransformer implements FessTransf
         }
 
         if (logger.isDebugEnabled()) {
-            logger.debug(attrValue + " -> " + u);
+            logger.debug("{} -> {}", attrValue, u);
         }
         if (StringUtil.isNotBlank(u)) {
             if (logger.isDebugEnabled()) {
-                logger.debug("Add Child: " + u);
+                logger.debug("Add Child: {}", u);
             }
             urlList.add(u);
         } else {
             if (logger.isDebugEnabled()) {
-                logger.debug("Skip Child: " + u);
+                logger.debug("Skip Child: {}", u);
             }
         }
     }
@@ -840,7 +840,7 @@ public class FessXpathTransformer extends XpathTransformer implements FessTransf
             for (int i = 0; i < imgNodeList.getLength(); i++) {
                 final Node imgNode = imgNodeList.item(i);
                 if (logger.isDebugEnabled()) {
-                    logger.debug("img tag: " + imgNode);
+                    logger.debug("img tag: {}", imgNode);
                 }
                 final NamedNodeMap attributes = imgNode.getAttributes();
                 final String thumbnailUrl = getThumbnailSrc(responseData.getUrl(), attributes);
@@ -854,7 +854,7 @@ public class FessXpathTransformer extends XpathTransformer implements FessTransf
                             return thumbnailUrl;
                         }
                     } catch (final Exception e) {
-                        logger.debug("Failed to parse " + imgNode + " at " + responseData.getUrl(), e);
+                        logger.debug("Failed to parse {} at {}", imgNode, responseData.getUrl(), e);
                     }
                 } else if (firstThumbnailUrl == null) {
                     firstThumbnailUrl = thumbnailUrl;
@@ -880,7 +880,7 @@ public class FessXpathTransformer extends XpathTransformer implements FessTransf
                 }
             } catch (final Exception e) {
                 if (logger.isDebugEnabled()) {
-                    logger.debug("Failed to parse thumbnail url for " + url + " : " + attributes, e);
+                    logger.debug("Failed to parse thumbnail url for {} : {}", url, attributes, e);
                 }
             }
         }
diff --git a/src/main/java/org/codelibs/fess/dict/DictionaryManager.java b/src/main/java/org/codelibs/fess/dict/DictionaryManager.java
index 3f8d513eb..3d8dcb8ff 100644
--- a/src/main/java/org/codelibs/fess/dict/DictionaryManager.java
+++ b/src/main/java/org/codelibs/fess/dict/DictionaryManager.java
@@ -42,7 +42,7 @@ public class DictionaryManager {
     @PostConstruct
     public void init() {
         if (logger.isDebugEnabled()) {
-            logger.debug("Initialize " + this.getClass().getSimpleName());
+            logger.debug("Initialize {}", this.getClass().getSimpleName());
         }
         creatorList.forEach(creator -> {
             creator.setDictionaryManager(this);
diff --git a/src/main/java/org/codelibs/fess/ds/DataStoreFactory.java b/src/main/java/org/codelibs/fess/ds/DataStoreFactory.java
index bb862908b..9b712b01e 100644
--- a/src/main/java/org/codelibs/fess/ds/DataStoreFactory.java
+++ b/src/main/java/org/codelibs/fess/ds/DataStoreFactory.java
@@ -57,7 +57,7 @@ public class DataStoreFactory {
             throw new IllegalArgumentException("name or dataStore is null.");
         }
         if (logger.isDebugEnabled()) {
-            logger.debug("Loaded " + name);
+            logger.debug("Loaded {}", name);
         }
         dataStoreMap.put(name.toLowerCase(Locale.ROOT), dataStore);
         dataStoreMap.put(dataStore.getClass().getSimpleName().toLowerCase(Locale.ROOT), dataStore);
diff --git a/src/main/java/org/codelibs/fess/ds/callback/FileListIndexUpdateCallbackImpl.java b/src/main/java/org/codelibs/fess/ds/callback/FileListIndexUpdateCallbackImpl.java
index 78e6f6949..f4dfbef38 100644
--- a/src/main/java/org/codelibs/fess/ds/callback/FileListIndexUpdateCallbackImpl.java
+++ b/src/main/java/org/codelibs/fess/ds/callback/FileListIndexUpdateCallbackImpl.java
@@ -75,7 +75,7 @@ public class FileListIndexUpdateCallbackImpl implements IndexUpdateCallback {
 
     protected ExecutorService newFixedThreadPool(final int nThreads) {
         if (logger.isDebugEnabled()) {
-            logger.debug("Executor Thread Pool: " + nThreads);
+            logger.debug("Executor Thread Pool: {}", nThreads);
         }
         return new ThreadPoolExecutor(nThreads, nThreads, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue<Runnable>(nThreads),
                 new ThreadPoolExecutor.CallerRunsPolicy());
@@ -191,7 +191,7 @@ public class FileListIndexUpdateCallbackImpl implements IndexUpdateCallback {
     protected boolean deleteDocument(final Map<String, String> paramMap, final Map<String, Object> dataMap) {
 
         if (logger.isDebugEnabled()) {
-            logger.debug("Deleting " + dataMap);
+            logger.debug("Deleting {}", dataMap);
         }
 
         final FessConfig fessConfig = ComponentUtil.getFessConfig();
@@ -242,7 +242,7 @@ public class FileListIndexUpdateCallbackImpl implements IndexUpdateCallback {
             indexingHelper.deleteDocumentByUrl(fessEsClient, url);
         }
         if (logger.isDebugEnabled()) {
-            logger.debug("Deleted " + deleteUrlList);
+            logger.debug("Deleted {}", deleteUrlList);
         }
         deleteUrlList.clear();
     }
diff --git a/src/main/java/org/codelibs/fess/ds/callback/IndexUpdateCallbackImpl.java b/src/main/java/org/codelibs/fess/ds/callback/IndexUpdateCallbackImpl.java
index 9644696e1..7bd9aa3af 100644
--- a/src/main/java/org/codelibs/fess/ds/callback/IndexUpdateCallbackImpl.java
+++ b/src/main/java/org/codelibs/fess/ds/callback/IndexUpdateCallbackImpl.java
@@ -50,7 +50,7 @@ public class IndexUpdateCallbackImpl implements IndexUpdateCallback {
     @PostConstruct
     public void init() {
         if (logger.isDebugEnabled()) {
-            logger.debug("Initialize " + this.getClass().getSimpleName());
+            logger.debug("Initialize {}", this.getClass().getSimpleName());
         }
         maxDocumentRequestSize = ComponentUtil.getFessConfig().getIndexerDataMaxDocumentRequestSizeAsInteger().longValue();
     }
@@ -65,7 +65,7 @@ public class IndexUpdateCallbackImpl implements IndexUpdateCallback {
         final FessEsClient fessEsClient = ComponentUtil.getFessEsClient();
 
         if (logger.isDebugEnabled()) {
-            logger.debug("Adding " + dataMap);
+            logger.debug("Adding {}", dataMap);
         }
 
         //   required check
@@ -107,7 +107,7 @@ public class IndexUpdateCallbackImpl implements IndexUpdateCallback {
         synchronized (docList) {
             docList.add(dataMap);
             if (logger.isDebugEnabled()) {
-                logger.debug("Added the document. " + "The number of a document cache is " + docList.size() + ".");
+                logger.debug("Added the document. The number of a document cache is {}.", docList.size());
             }
 
             final Long contentLength = DocumentUtil.getValue(dataMap, fessConfig.getIndexFieldContentLength(), Long.class);
@@ -125,7 +125,7 @@ public class IndexUpdateCallbackImpl implements IndexUpdateCallback {
         documentSize.getAndIncrement();
 
         if (logger.isDebugEnabled()) {
-            logger.debug("The number of an added document is " + documentSize.get() + ".");
+            logger.debug("The number of an added document is {}.", documentSize.get());
         }
 
     }
@@ -146,7 +146,7 @@ public class IndexUpdateCallbackImpl implements IndexUpdateCallback {
         final int count = searchLogHelper.getClickCount(url);
         doc.put(clickCountField, count);
         if (logger.isDebugEnabled()) {
-            logger.debug("Click Count: " + count + ", url: " + url);
+            logger.debug("Click Count: {}, url: {}", count, url);
         }
     }
 
@@ -155,7 +155,7 @@ public class IndexUpdateCallbackImpl implements IndexUpdateCallback {
         final long count = searchLogHelper.getFavoriteCount(url);
         doc.put(favoriteCountField, count);
         if (logger.isDebugEnabled()) {
-            logger.debug("Favorite Count: " + count + ", url: " + url);
+            logger.debug("Favorite Count: {}, url: {}", count, url);
         }
     }
 
diff --git a/src/main/java/org/codelibs/fess/es/client/FessEsClient.java b/src/main/java/org/codelibs/fess/es/client/FessEsClient.java
index 586a0b6a9..b8b56be70 100644
--- a/src/main/java/org/codelibs/fess/es/client/FessEsClient.java
+++ b/src/main/java/org/codelibs/fess/es/client/FessEsClient.java
@@ -233,7 +233,7 @@ public class FessEsClient implements Client {
     @PostConstruct
     public void open() {
         if (logger.isDebugEnabled()) {
-            logger.debug("Initialize " + this.getClass().getSimpleName());
+            logger.debug("Initialize {}", this.getClass().getSimpleName());
         }
         final FessConfig fessConfig = ComponentUtil.getFessConfig();
 
@@ -392,7 +392,7 @@ public class FessEsClient implements Client {
                 logger.info("Created " + indexName + " index.");
                 return true;
             } else if (logger.isDebugEnabled()) {
-                logger.debug("Failed to create " + indexName + " index.");
+                logger.debug("Failed to create {} index.", indexName);
             }
         } catch (final Exception e) {
             logger.warn(indexConfigFile + " is not found.", e);
@@ -433,7 +433,7 @@ public class FessEsClient implements Client {
                 logger.warn("Failed to create " + indexName + "/" + docType + " mapping.", e);
             }
         } else if (logger.isDebugEnabled()) {
-            logger.debug(indexName + "/" + docType + " mapping exists.");
+            logger.debug("{}/{} mapping exists.", indexName, docType);
         }
     }
 
@@ -480,7 +480,7 @@ public class FessEsClient implements Client {
                             if (response.isAcknowledged()) {
                                 logger.info("Created " + aliasName + " alias for " + createdIndexName);
                             } else if (logger.isDebugEnabled()) {
-                                logger.debug("Failed to create " + aliasName + " alias for " + createdIndexName);
+                                logger.debug("Failed to create {} alias for {}", aliasName, createdIndexName);
                             }
                         }));
             }
@@ -581,14 +581,14 @@ public class FessEsClient implements Client {
                         client.admin().cluster().prepareHealth().setWaitForYellowStatus().execute()
                                 .actionGet(fessConfig.getIndexHealthTimeout());
                 if (logger.isDebugEnabled()) {
-                    logger.debug("Elasticsearch Cluster Status: " + response.getStatus());
+                    logger.debug("Elasticsearch Cluster Status: {}", response.getStatus());
                 }
                 return;
             } catch (final Exception e) {
                 cause = e;
             }
             if (logger.isDebugEnabled()) {
-                logger.debug("Failed to access to Elasticsearch:" + i, cause);
+                logger.debug("Failed to access to Elasticsearch:{}", i, cause);
             }
             try {
                 Thread.sleep(1000L);
@@ -623,7 +623,7 @@ public class FessEsClient implements Client {
                 cause = new FessSystemException("Configsync is not available.", e);
             }
             if (logger.isDebugEnabled()) {
-                logger.debug("Failed to access to configsync:" + i, cause);
+                logger.debug("Failed to access to configsync:{}", i, cause);
             }
             try {
                 Thread.sleep(1000L);
@@ -779,7 +779,7 @@ public class FessEsClient implements Client {
 
             try {
                 if (logger.isDebugEnabled()) {
-                    logger.debug("Query DSL:\n" + searchRequestBuilder.toString());
+                    logger.debug("Query DSL:\n{}", searchRequestBuilder.toString());
                 }
                 searchResponse = searchRequestBuilder.execute().actionGet(ComponentUtil.getFessConfig().getIndexSearchTimeout());
             } catch (final SearchPhaseExecutionException e) {
@@ -803,7 +803,7 @@ public class FessEsClient implements Client {
             String scrollId = null;
             try {
                 if (logger.isDebugEnabled()) {
-                    logger.debug("Query DSL:\n" + searchRequestBuilder.toString());
+                    logger.debug("Query DSL:\n{}", searchRequestBuilder.toString());
                 }
                 SearchResponse response = searchRequestBuilder.execute().actionGet(ComponentUtil.getFessConfig().getIndexSearchTimeout());
 
@@ -1004,7 +1004,7 @@ public class FessEsClient implements Client {
                         if (resp.isFailed() && resp.getFailure() != null) {
                             final DocWriteRequest<?> req = requests.get(i);
                             final Failure failure = resp.getFailure();
-                            logger.debug("Failed Request: " + req + "\n=>" + failure.getMessage());
+                            logger.debug("Failed Request: {}\n=>{}", req, failure.getMessage());
                         }
                     }
                 }
diff --git a/src/main/java/org/codelibs/fess/es/config/exbhv/ScheduledJobBhv.java b/src/main/java/org/codelibs/fess/es/config/exbhv/ScheduledJobBhv.java
index 625d64181..356097bb1 100644
--- a/src/main/java/org/codelibs/fess/es/config/exbhv/ScheduledJobBhv.java
+++ b/src/main/java/org/codelibs/fess/es/config/exbhv/ScheduledJobBhv.java
@@ -51,7 +51,7 @@ public class ScheduledJobBhv extends BsScheduledJobBhv {
                 return super.selectByPK(id);
             } catch (final Exception e) {
                 if (logger.isDebugEnabled()) {
-                    logger.debug("Failed to select a job by " + id, e);
+                    logger.debug("Failed to select a job by {}", id, e);
                 }
                 lastException = e;
                 try {
diff --git a/src/main/java/org/codelibs/fess/es/config/exentity/DataConfig.java b/src/main/java/org/codelibs/fess/es/config/exentity/DataConfig.java
index 248261d21..e4ded8ac5 100644
--- a/src/main/java/org/codelibs/fess/es/config/exentity/DataConfig.java
+++ b/src/main/java/org/codelibs/fess/es/config/exentity/DataConfig.java
@@ -400,7 +400,7 @@ public class DataConfig extends BsDataConfig implements CrawlingConfig {
             return Integer.parseInt(value);
         } catch (final NumberFormatException e) {
             if (logger.isDebugEnabled()) {
-                logger.debug("Invalid format: " + value, e);
+                logger.debug("Invalid format: {}", value, e);
             }
         }
         return null;
diff --git a/src/main/java/org/codelibs/fess/es/log/exbhv/ClickLogBhv.java b/src/main/java/org/codelibs/fess/es/log/exbhv/ClickLogBhv.java
index d6d3a3826..f3a86e6b9 100644
--- a/src/main/java/org/codelibs/fess/es/log/exbhv/ClickLogBhv.java
+++ b/src/main/java/org/codelibs/fess/es/log/exbhv/ClickLogBhv.java
@@ -53,7 +53,7 @@ public class ClickLogBhv extends BsClickLogBhv {
                 final LocalDateTime date = LocalDateTime.ofInstant(instant, ZoneId.systemDefault());
                 return date;
             } catch (final DateTimeParseException e) {
-                logger.debug("Invalid date format: " + value, e);
+                logger.debug("Invalid date format: {}", value, e);
             }
         }
         return DfTypeUtil.toLocalDateTime(value);
diff --git a/src/main/java/org/codelibs/fess/es/log/exbhv/FavoriteLogBhv.java b/src/main/java/org/codelibs/fess/es/log/exbhv/FavoriteLogBhv.java
index ba7deddc9..52dfada79 100644
--- a/src/main/java/org/codelibs/fess/es/log/exbhv/FavoriteLogBhv.java
+++ b/src/main/java/org/codelibs/fess/es/log/exbhv/FavoriteLogBhv.java
@@ -53,7 +53,7 @@ public class FavoriteLogBhv extends BsFavoriteLogBhv {
                 final LocalDateTime date = LocalDateTime.ofInstant(instant, ZoneId.systemDefault());
                 return date;
             } catch (final DateTimeParseException e) {
-                logger.debug("Invalid date format: " + value, e);
+                logger.debug("Invalid date format: {}", value, e);
             }
         }
         return DfTypeUtil.toLocalDateTime(value);
diff --git a/src/main/java/org/codelibs/fess/es/log/exbhv/SearchLogBhv.java b/src/main/java/org/codelibs/fess/es/log/exbhv/SearchLogBhv.java
index d69f0a7a3..58426a7c6 100644
--- a/src/main/java/org/codelibs/fess/es/log/exbhv/SearchLogBhv.java
+++ b/src/main/java/org/codelibs/fess/es/log/exbhv/SearchLogBhv.java
@@ -58,7 +58,7 @@ public class SearchLogBhv extends BsSearchLogBhv {
                 final LocalDateTime date = LocalDateTime.ofInstant(instant, ZoneId.systemDefault());
                 return date;
             } catch (final DateTimeParseException e) {
-                logger.debug("Invalid date format: " + value, e);
+                logger.debug("Invalid date format: {}", value, e);
             }
         }
         return DfTypeUtil.toLocalDateTime(value);
diff --git a/src/main/java/org/codelibs/fess/es/log/exbhv/UserInfoBhv.java b/src/main/java/org/codelibs/fess/es/log/exbhv/UserInfoBhv.java
index d4c1486d2..ee2013054 100644
--- a/src/main/java/org/codelibs/fess/es/log/exbhv/UserInfoBhv.java
+++ b/src/main/java/org/codelibs/fess/es/log/exbhv/UserInfoBhv.java
@@ -53,7 +53,7 @@ public class UserInfoBhv extends BsUserInfoBhv {
                 final LocalDateTime date = LocalDateTime.ofInstant(instant, ZoneId.systemDefault());
                 return date;
             } catch (final DateTimeParseException e) {
-                logger.debug("Invalid date format: " + value, e);
+                logger.debug("Invalid date format: {}", value, e);
             }
         }
         return DfTypeUtil.toLocalDateTime(value);
diff --git a/src/main/java/org/codelibs/fess/exec/Crawler.java b/src/main/java/org/codelibs/fess/exec/Crawler.java
index cbe3240e3..0930e16eb 100644
--- a/src/main/java/org/codelibs/fess/exec/Crawler.java
+++ b/src/main/java/org/codelibs/fess/exec/Crawler.java
@@ -192,10 +192,10 @@ public class Crawler {
 
         if (logger.isDebugEnabled()) {
             try {
-                ManagementFactory.getRuntimeMXBean().getInputArguments().stream().forEach(s -> logger.debug("Parameter: " + s));
-                System.getProperties().entrySet().stream().forEach(e -> logger.debug("Property: " + e.getKey() + "=" + e.getValue()));
-                System.getenv().entrySet().forEach(e -> logger.debug("Env: " + e.getKey() + "=" + e.getValue()));
-                logger.debug("Option: " + options);
+                ManagementFactory.getRuntimeMXBean().getInputArguments().stream().forEach(s -> logger.debug("Parameter: {}", s));
+                System.getProperties().entrySet().stream().forEach(e -> logger.debug("Property: {}={}", e.getKey(), e.getValue()));
+                System.getenv().entrySet().forEach(e -> logger.debug("Env: {}={}", e.getKey(), e.getValue()));
+                logger.debug("Option: {}", options);
             } catch (final Exception e) {
                 // ignore
             }
@@ -237,7 +237,7 @@ public class Crawler {
                             }
                             command = reader.readLine().trim();
                             if (logger.isDebugEnabled()) {
-                                logger.debug("Process command: " + command);
+                                logger.debug("Process command: {}", command);
                             }
                             if (Constants.CRAWLER_PROCESS_COMMAND_THREAD_DUMP.equals(command)) {
                                 ThreadDumpUtil.printThreadDump();
@@ -316,7 +316,7 @@ public class Crawler {
             try {
                 final File propFile = ComponentUtil.getSystemHelper().createTempFile("crawler_", ".properties");
                 if (propFile.delete() && logger.isDebugEnabled()) {
-                    logger.debug("Deleted a temp file: " + propFile.getAbsolutePath());
+                    logger.debug("Deleted a temp file: {}", propFile.getAbsolutePath());
                 }
                 systemProperties.reload(propFile.getAbsolutePath());
                 propFile.deleteOnExit();
diff --git a/src/main/java/org/codelibs/fess/exec/SuggestCreator.java b/src/main/java/org/codelibs/fess/exec/SuggestCreator.java
index abffcf7f8..a0d7f0a9f 100644
--- a/src/main/java/org/codelibs/fess/exec/SuggestCreator.java
+++ b/src/main/java/org/codelibs/fess/exec/SuggestCreator.java
@@ -94,10 +94,10 @@ public class SuggestCreator {
 
         if (logger.isDebugEnabled()) {
             try {
-                ManagementFactory.getRuntimeMXBean().getInputArguments().stream().forEach(s -> logger.debug("Parameter: " + s));
-                System.getProperties().entrySet().stream().forEach(e -> logger.debug("Property: " + e.getKey() + "=" + e.getValue()));
-                System.getenv().entrySet().forEach(e -> logger.debug("Env: " + e.getKey() + "=" + e.getValue()));
-                logger.debug("Option: " + options);
+                ManagementFactory.getRuntimeMXBean().getInputArguments().stream().forEach(s -> logger.debug("Parameter: {}", s));
+                System.getProperties().entrySet().stream().forEach(e -> logger.debug("Property: {}={}", e.getKey(), e.getValue()));
+                System.getenv().entrySet().forEach(e -> logger.debug("Env: {}={}", e.getKey(), e.getValue()));
+                logger.debug("Option: {}", options);
             } catch (final Exception e) {
                 // ignore
             }
@@ -169,7 +169,7 @@ public class SuggestCreator {
             try {
                 final File propFile = ComponentUtil.getSystemHelper().createTempFile("suggest_", ".properties");
                 if (propFile.delete() && logger.isDebugEnabled()) {
-                    logger.debug("Deleted a temp file: " + propFile.getAbsolutePath());
+                    logger.debug("Deleted a temp file: {}", propFile.getAbsolutePath());
                 }
                 systemProperties.reload(propFile.getAbsolutePath());
                 propFile.deleteOnExit();
diff --git a/src/main/java/org/codelibs/fess/exec/ThumbnailGenerator.java b/src/main/java/org/codelibs/fess/exec/ThumbnailGenerator.java
index fe8c8a3c5..aa44d1cb5 100644
--- a/src/main/java/org/codelibs/fess/exec/ThumbnailGenerator.java
+++ b/src/main/java/org/codelibs/fess/exec/ThumbnailGenerator.java
@@ -102,10 +102,10 @@ public class ThumbnailGenerator {
 
         if (logger.isDebugEnabled()) {
             try {
-                ManagementFactory.getRuntimeMXBean().getInputArguments().stream().forEach(s -> logger.debug("Parameter: " + s));
-                System.getProperties().entrySet().stream().forEach(e -> logger.debug("Property: " + e.getKey() + "=" + e.getValue()));
-                System.getenv().entrySet().forEach(e -> logger.debug("Env: " + e.getKey() + "=" + e.getValue()));
-                logger.debug("Option: " + options);
+                ManagementFactory.getRuntimeMXBean().getInputArguments().stream().forEach(s -> logger.debug("Parameter: {}", s));
+                System.getProperties().entrySet().stream().forEach(e -> logger.debug("Property: {}={}", e.getKey(), e.getValue()));
+                System.getenv().entrySet().forEach(e -> logger.debug("Env: {}={}", e.getKey(), e.getValue()));
+                logger.debug("Option: {}", options);
             } catch (final Exception e) {
                 // ignore
             }
@@ -182,7 +182,7 @@ public class ThumbnailGenerator {
             try {
                 final File propFile = ComponentUtil.getSystemHelper().createTempFile("thumbnail_", ".properties");
                 if (propFile.delete() && logger.isDebugEnabled()) {
-                    logger.debug("Deleted a temp file: " + propFile.getAbsolutePath());
+                    logger.debug("Deleted a temp file: {}", propFile.getAbsolutePath());
                 }
                 systemProperties.reload(propFile.getAbsolutePath());
                 propFile.deleteOnExit();
diff --git a/src/main/java/org/codelibs/fess/filter/CorsFilter.java b/src/main/java/org/codelibs/fess/filter/CorsFilter.java
index 057ad71d0..45194465c 100644
--- a/src/main/java/org/codelibs/fess/filter/CorsFilter.java
+++ b/src/main/java/org/codelibs/fess/filter/CorsFilter.java
@@ -60,7 +60,7 @@ public class CorsFilter implements Filter {
         }
 
         if (logger.isDebugEnabled()) {
-            logger.debug("HTTP Request: " + httpRequest.getMethod());
+            logger.debug("HTTP Request: {}", httpRequest.getMethod());
         }
 
         final FessConfig fessConfig = ComponentUtil.getFessConfig();
@@ -68,7 +68,7 @@ public class CorsFilter implements Filter {
         final String allowOrigin = getAllowOrigin(fessConfig, origin);
         if (StringUtil.isNotBlank(allowOrigin)) {
             if (logger.isDebugEnabled()) {
-                logger.debug("allowOrigin: " + allowOrigin);
+                logger.debug("allowOrigin: {}", allowOrigin);
             }
             final HttpServletResponse httpResponse = (HttpServletResponse) response;
             httpResponse.addHeader(ACCESS_CONTROL_ALLOW_ORIGIN, allowOrigin);
diff --git a/src/main/java/org/codelibs/fess/helper/CrawlingConfigHelper.java b/src/main/java/org/codelibs/fess/helper/CrawlingConfigHelper.java
index daddea600..0f15cb391 100644
--- a/src/main/java/org/codelibs/fess/helper/CrawlingConfigHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/CrawlingConfigHelper.java
@@ -66,7 +66,7 @@ public class CrawlingConfigHelper {
     @PostConstruct
     public void init() {
         if (logger.isDebugEnabled()) {
-            logger.debug("Initialize " + this.getClass().getSimpleName());
+            logger.debug("Initialize {}", this.getClass().getSimpleName());
         }
         crawlingConfigCache = CacheBuilder.newBuilder().maximumSize(100).expireAfterWrite(10, TimeUnit.MINUTES).build();
     }
diff --git a/src/main/java/org/codelibs/fess/helper/DocumentHelper.java b/src/main/java/org/codelibs/fess/helper/DocumentHelper.java
index bb6d1e03b..e0ae0a7f7 100644
--- a/src/main/java/org/codelibs/fess/helper/DocumentHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/DocumentHelper.java
@@ -71,7 +71,7 @@ public class DocumentHelper {
     @PostConstruct
     public void init() {
         if (logger.isDebugEnabled()) {
-            logger.debug("Initialize " + this.getClass().getSimpleName());
+            logger.debug("Initialize {}", this.getClass().getSimpleName());
         }
         try {
             final TikaExtractor tikaExtractor = ComponentUtil.getComponent("tikaExtractor");
@@ -234,7 +234,7 @@ public class DocumentHelper {
                 return ReaderUtil.readText(reader);
             } catch (final IOException e) {
                 if (logger.isDebugEnabled()) {
-                    logger.debug("Failed to decode " + hash, e);
+                    logger.debug("Failed to decode {}", hash, e);
                 }
             }
         }
diff --git a/src/main/java/org/codelibs/fess/helper/DuplicateHostHelper.java b/src/main/java/org/codelibs/fess/helper/DuplicateHostHelper.java
index a15d900a6..1f8559a6a 100644
--- a/src/main/java/org/codelibs/fess/helper/DuplicateHostHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/DuplicateHostHelper.java
@@ -34,7 +34,7 @@ public class DuplicateHostHelper {
     @PostConstruct
     public void init() {
         if (logger.isDebugEnabled()) {
-            logger.debug("Initialize " + this.getClass().getSimpleName());
+            logger.debug("Initialize {}", this.getClass().getSimpleName());
         }
         if (duplicateHostList == null) {
             duplicateHostList = new ArrayList<>();
diff --git a/src/main/java/org/codelibs/fess/helper/IndexingHelper.java b/src/main/java/org/codelibs/fess/helper/IndexingHelper.java
index a227c8baa..fe0b80cf3 100644
--- a/src/main/java/org/codelibs/fess/helper/IndexingHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/IndexingHelper.java
@@ -52,7 +52,7 @@ public class IndexingHelper {
         }
         final long execTime = System.currentTimeMillis();
         if (logger.isDebugEnabled()) {
-            logger.debug("Sending " + docList.size() + " documents to a server.");
+            logger.debug("Sending {} documents to a server.", docList.size());
         }
         try {
             if (fessConfig.isThumbnailCrawlerEnabled()) {
@@ -61,8 +61,8 @@ public class IndexingHelper {
                         doc -> {
                             if (!thumbnailManager.offer(doc)) {
                                 if (logger.isDebugEnabled()) {
-                                    logger.debug("Removing " + doc.get(fessConfig.getIndexFieldThumbnail()) + " from "
-                                            + doc.get(fessConfig.getIndexFieldUrl()));
+                                    logger.debug("Removing {} from {}", doc.get(fessConfig.getIndexFieldThumbnail()),
+                                            doc.get(fessConfig.getIndexFieldUrl()));
                                 }
                                 doc.remove(fessConfig.getIndexFieldThumbnail());
                             }
@@ -124,7 +124,7 @@ public class IndexingHelper {
                 }
             }
             if (logger.isDebugEnabled()) {
-                logger.debug(queryBuilder.toString() + " => " + docs);
+                logger.debug("{} => {}", queryBuilder.toString(), docs);
             }
         }
         if (!docIdList.isEmpty()) {
diff --git a/src/main/java/org/codelibs/fess/helper/JobHelper.java b/src/main/java/org/codelibs/fess/helper/JobHelper.java
index 65db5b93a..38f16c393 100644
--- a/src/main/java/org/codelibs/fess/helper/JobHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/JobHelper.java
@@ -61,7 +61,7 @@ public class JobHelper {
                 unregister(scheduledJob);
             } catch (final Exception e) {
                 if (logger.isDebugEnabled()) {
-                    logger.debug("Failed to delete Job " + scheduledJob, e);
+                    logger.debug("Failed to delete Job {}", scheduledJob, e);
                 }
             }
             return;
@@ -176,7 +176,7 @@ public class JobHelper {
             if (jobLog.getEndTime() == null) {
                 jobLog.setLastUpdated(ComponentUtil.getSystemHelper().getCurrentTimeAsLong());
                 if (logger.isDebugEnabled()) {
-                    logger.debug("Update " + jobLog);
+                    logger.debug("Update {}", jobLog);
                 }
                 ComponentUtil.getComponent(JobLogBhv.class).insertOrUpdate(jobLog, op -> {
                     op.setRefreshPolicy(Constants.TRUE);
diff --git a/src/main/java/org/codelibs/fess/helper/KeyMatchHelper.java b/src/main/java/org/codelibs/fess/helper/KeyMatchHelper.java
index 990cf1622..d68710545 100644
--- a/src/main/java/org/codelibs/fess/helper/KeyMatchHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/KeyMatchHelper.java
@@ -54,7 +54,7 @@ public class KeyMatchHelper {
     @PostConstruct
     public void init() {
         if (logger.isDebugEnabled()) {
-            logger.debug("Initialize " + this.getClass().getSimpleName());
+            logger.debug("Initialize {}", this.getClass().getSimpleName());
         }
         reload(0);
     }
@@ -77,11 +77,11 @@ public class KeyMatchHelper {
                 keyMatch -> {
                     final BoolQueryBuilder boolQuery = QueryBuilders.boolQuery();
                     if (logger.isDebugEnabled()) {
-                        logger.debug("Loading KeyMatch Query: " + keyMatch.getQuery() + ", Size: " + keyMatch.getMaxSize());
+                        logger.debug("Loading KeyMatch Query: {}, Size: {}", keyMatch.getQuery(), keyMatch.getMaxSize());
                     }
                     getDocumentList(keyMatch).stream().map(doc -> {
                         if (logger.isDebugEnabled()) {
-                            logger.debug("Loaded KeyMatch doc: " + doc);
+                            logger.debug("Loaded KeyMatch doc: {}", doc);
                         }
                         return DocumentUtil.getValue(doc, fessConfig.getIndexFieldDocId(), String.class);
                     }).forEach(docId -> {
@@ -90,7 +90,7 @@ public class KeyMatchHelper {
 
                     if (boolQuery.hasClauses()) {
                         if (logger.isDebugEnabled()) {
-                            logger.debug("Loaded KeyMatch Boost Query: " + boolQuery);
+                            logger.debug("Loaded KeyMatch Boost Query: {}", boolQuery);
                         }
                         String virtualHost = keyMatch.getVirtualHost();
                         if (StringUtil.isBlank(virtualHost)) {
diff --git a/src/main/java/org/codelibs/fess/helper/LabelTypeHelper.java b/src/main/java/org/codelibs/fess/helper/LabelTypeHelper.java
index b69f4dabf..95c45ff3a 100644
--- a/src/main/java/org/codelibs/fess/helper/LabelTypeHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/LabelTypeHelper.java
@@ -48,7 +48,7 @@ public class LabelTypeHelper {
     @PostConstruct
     public void init() {
         if (logger.isDebugEnabled()) {
-            logger.debug("Initialize " + this.getClass().getSimpleName());
+            logger.debug("Initialize {}", this.getClass().getSimpleName());
         }
         update();
     }
@@ -258,20 +258,20 @@ public class LabelTypeHelper {
                 if (includedPaths.matcher(path).matches()) {
                     if (excludedPaths != null && excludedPaths.matcher(path).matches()) {
                         if (logger.isDebugEnabled()) {
-                            logger.debug("Path " + path + " matched against the excludes paths expression " + excludedPaths.toString());
+                            logger.debug("Path {} matched against the excludes paths expression {}", path, excludedPaths.toString());
                         }
                         return false;
                     }
                     return true;
                 }
                 if (logger.isDebugEnabled()) {
-                    logger.debug("Path " + path + " wasn't matched against the include paths expression " + includedPaths.toString());
+                    logger.debug("Path {} wasn't matched against the include paths expression {}" , path, includedPaths.toString());
                 }
                 return false;
             } else {
                 if (excludedPaths != null && excludedPaths.matcher(path).matches()) {
                     if (logger.isDebugEnabled()) {
-                        logger.debug("Path " + path + " matched against the excludes paths expression " + excludedPaths.toString());
+                        logger.debug("Path {} matched against the excludes paths expression {}", path, excludedPaths.toString());
                     }
                     return false;
                 }
diff --git a/src/main/java/org/codelibs/fess/helper/LanguageHelper.java b/src/main/java/org/codelibs/fess/helper/LanguageHelper.java
index 1e7f9ce5a..b741b67cc 100644
--- a/src/main/java/org/codelibs/fess/helper/LanguageHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/LanguageHelper.java
@@ -42,7 +42,7 @@ public class LanguageHelper {
     @PostConstruct
     public void init() {
         if (logger.isDebugEnabled()) {
-            logger.debug("Initialize " + this.getClass().getSimpleName());
+            logger.debug("Initialize {}", this.getClass().getSimpleName());
         }
         final FessConfig fessConfig = ComponentUtil.getFessConfig();
         langFields = fessConfig.getIndexerLanguageFieldsAsArray();
diff --git a/src/main/java/org/codelibs/fess/helper/OpenSearchHelper.java b/src/main/java/org/codelibs/fess/helper/OpenSearchHelper.java
index 615b850d2..8b7381df7 100644
--- a/src/main/java/org/codelibs/fess/helper/OpenSearchHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/OpenSearchHelper.java
@@ -49,7 +49,7 @@ public class OpenSearchHelper {
     @PostConstruct
     public void init() {
         if (logger.isDebugEnabled()) {
-            logger.debug("Initialize " + this.getClass().getSimpleName());
+            logger.debug("Initialize {}", this.getClass().getSimpleName());
         }
         if (StringUtil.isNotBlank(osddPath)) {
             final String path = LaServletContextUtil.getServletContext().getRealPath(osddPath);
diff --git a/src/main/java/org/codelibs/fess/helper/PathMappingHelper.java b/src/main/java/org/codelibs/fess/helper/PathMappingHelper.java
index 6fb6b2494..7dac892f3 100644
--- a/src/main/java/org/codelibs/fess/helper/PathMappingHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/PathMappingHelper.java
@@ -52,7 +52,7 @@ public class PathMappingHelper {
     @PostConstruct
     public void init() {
         if (logger.isDebugEnabled()) {
-            logger.debug("Initialize " + this.getClass().getSimpleName());
+            logger.debug("Initialize {}", this.getClass().getSimpleName());
         }
         update();
     }
diff --git a/src/main/java/org/codelibs/fess/helper/PermissionHelper.java b/src/main/java/org/codelibs/fess/helper/PermissionHelper.java
index 0def78cc4..8ee209a2d 100644
--- a/src/main/java/org/codelibs/fess/helper/PermissionHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/PermissionHelper.java
@@ -167,7 +167,7 @@ public class PermissionHelper {
                     }
                 }
                 if (logger.isDebugEnabled()) {
-                    logger.debug("smbUrl:" + responseData.getUrl() + " roleType:" + roleTypeList.toString());
+                    logger.debug("smbUrl:{} roleType:{}", responseData.getUrl(), roleTypeList.toString());
                 }
             } else if (responseData.getUrl().startsWith("smb1:")) {
                 final jcifs.smb1.smb1.SID[] allowedSids =
@@ -191,7 +191,7 @@ public class PermissionHelper {
                     }
                 }
                 if (logger.isDebugEnabled()) {
-                    logger.debug("smb1Url:" + responseData.getUrl() + " roleType:" + roleTypeList.toString());
+                    logger.debug("smb1Url:{} roleType:{}", responseData.getUrl(), roleTypeList.toString());
                 }
             }
         }
@@ -210,7 +210,7 @@ public class PermissionHelper {
             final String[] groups = (String[]) responseData.getMetaDataMap().get(FileSystemClient.FS_FILE_GROUPS);
             roleTypeList.addAll(stream(groups).get(stream -> stream.map(systemHelper::getSearchRoleByGroup).collect(Collectors.toList())));
             if (logger.isDebugEnabled()) {
-                logger.debug("fileUrl:" + responseData.getUrl() + " roleType:" + roleTypeList.toString());
+                logger.debug("fileUrl:{} roleType:{}", responseData.getUrl(), roleTypeList.toString());
             }
         }
         return roleTypeList;
@@ -230,7 +230,7 @@ public class PermissionHelper {
                 roleTypeList.add(systemHelper.getSearchRoleByGroup(group));
             }
             if (logger.isDebugEnabled()) {
-                logger.debug("ftpUrl:" + responseData.getUrl() + " roleType:" + roleTypeList.toString());
+                logger.debug("ftpUrl:{} roleType:{}", responseData.getUrl(), roleTypeList.toString());
             }
         }
         return roleTypeList;
diff --git a/src/main/java/org/codelibs/fess/helper/PluginHelper.java b/src/main/java/org/codelibs/fess/helper/PluginHelper.java
index c40aee625..8b3bd9c60 100644
--- a/src/main/java/org/codelibs/fess/helper/PluginHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/PluginHelper.java
@@ -134,13 +134,13 @@ public class PluginHelper {
                                 final String actualVersion = version.replace("SNAPSHOT", snapshotVersion);
                                 list.add(new Artifact(name, actualVersion, pluginUrl + version + "/" + name + "-" + actualVersion + ".jar"));
                             } else if (logger.isDebugEnabled()) {
-                                logger.debug("Snapshot name is not found: " + name + "/" + version);
+                                logger.debug("Snapshot name is not found: {}/{}", name, version);
                             }
                         } else {
                             list.add(new Artifact(name, version, pluginUrl + version + "/" + name + "-" + version + ".jar"));
                         }
                     } else if (logger.isDebugEnabled()) {
-                        logger.debug(name + ":" + version + " is ignored.");
+                        logger.debug("{}:{} is ignored.", name, version);
                     }
                 }
             } catch (final Exception e) {
@@ -182,7 +182,7 @@ public class PluginHelper {
 
     protected String getRepositoryContent(final String url) {
         if (logger.isDebugEnabled()) {
-            logger.debug("Loading " + url);
+            logger.debug("Loading {}", url);
         }
         try (final CurlResponse response = Curl.get(url).execute()) {
             return response.getContentAsString();
diff --git a/src/main/java/org/codelibs/fess/helper/PopularWordHelper.java b/src/main/java/org/codelibs/fess/helper/PopularWordHelper.java
index 65d399eee..e592ce6bd 100644
--- a/src/main/java/org/codelibs/fess/helper/PopularWordHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/PopularWordHelper.java
@@ -49,7 +49,7 @@ public class PopularWordHelper {
     @PostConstruct
     public void init() {
         if (logger.isDebugEnabled()) {
-            logger.debug("Initialize " + this.getClass().getSimpleName());
+            logger.debug("Initialize {}", this.getClass().getSimpleName());
         }
         fessConfig = ComponentUtil.getFessConfig();
         cache =
diff --git a/src/main/java/org/codelibs/fess/helper/QueryHelper.java b/src/main/java/org/codelibs/fess/helper/QueryHelper.java
index 077b386ec..f87be4814 100644
--- a/src/main/java/org/codelibs/fess/helper/QueryHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/QueryHelper.java
@@ -140,7 +140,7 @@ public class QueryHelper {
     @PostConstruct
     public void init() {
         if (logger.isDebugEnabled()) {
-            logger.debug("Initialize " + this.getClass().getSimpleName());
+            logger.debug("Initialize {}", this.getClass().getSimpleName());
         }
         final FessConfig fessConfig = ComponentUtil.getFessConfig();
         if (responseFields == null) {
diff --git a/src/main/java/org/codelibs/fess/helper/RelatedContentHelper.java b/src/main/java/org/codelibs/fess/helper/RelatedContentHelper.java
index 5bd6e74f9..db77af386 100644
--- a/src/main/java/org/codelibs/fess/helper/RelatedContentHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/RelatedContentHelper.java
@@ -46,7 +46,7 @@ public class RelatedContentHelper {
     @PostConstruct
     public void init() {
         if (logger.isDebugEnabled()) {
-            logger.debug("Initialize " + this.getClass().getSimpleName());
+            logger.debug("Initialize {}", this.getClass().getSimpleName());
         }
         reload();
     }
diff --git a/src/main/java/org/codelibs/fess/helper/RelatedQueryHelper.java b/src/main/java/org/codelibs/fess/helper/RelatedQueryHelper.java
index 7d9cc3cbe..b3d364e6f 100644
--- a/src/main/java/org/codelibs/fess/helper/RelatedQueryHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/RelatedQueryHelper.java
@@ -38,7 +38,7 @@ public class RelatedQueryHelper {
     @PostConstruct
     public void init() {
         if (logger.isDebugEnabled()) {
-            logger.debug("Initialize " + this.getClass().getSimpleName());
+            logger.debug("Initialize {}", this.getClass().getSimpleName());
         }
         reload();
     }
diff --git a/src/main/java/org/codelibs/fess/helper/RoleQueryHelper.java b/src/main/java/org/codelibs/fess/helper/RoleQueryHelper.java
index acd787eb7..8b7614f0e 100644
--- a/src/main/java/org/codelibs/fess/helper/RoleQueryHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/RoleQueryHelper.java
@@ -80,7 +80,7 @@ public class RoleQueryHelper {
     @PostConstruct
     public void init() {
         if (logger.isDebugEnabled()) {
-            logger.debug("Initialize " + this.getClass().getSimpleName());
+            logger.debug("Initialize {}", this.getClass().getSimpleName());
         }
         stream(ComponentUtil.getFessConfig().getSearchDefaultPermissionsAsArray()).of(stream -> stream.forEach(name -> {
             defaultRoleList.add(name);
@@ -150,7 +150,7 @@ public class RoleQueryHelper {
         }
 
         if (logger.isDebugEnabled()) {
-            logger.debug("roleSet: " + roleSet);
+            logger.debug("roleSet: {}", roleSet);
         }
 
         if (request != null) {
@@ -172,7 +172,7 @@ public class RoleQueryHelper {
     protected void processParameter(final HttpServletRequest request, final Set<String> roleSet) {
         final String parameter = request.getParameter(parameterKey);
         if (logger.isDebugEnabled()) {
-            logger.debug(parameterKey + ":" + parameter);
+            logger.debug("{}:{}", parameterKey, parameter);
         }
         if (StringUtil.isNotEmpty(parameter)) {
             parseRoleSet(parameter, encryptedParameterValue, roleSet);
@@ -184,7 +184,7 @@ public class RoleQueryHelper {
 
         final String parameter = request.getHeader(headerKey);
         if (logger.isDebugEnabled()) {
-            logger.debug(headerKey + ":" + parameter);
+            logger.debug("{}:{}", headerKey, parameter);
         }
         if (StringUtil.isNotEmpty(parameter)) {
             parseRoleSet(parameter, encryptedHeaderValue, roleSet);
@@ -200,7 +200,7 @@ public class RoleQueryHelper {
                 if (cookieKey.equals(cookie.getName())) {
                     final String value = cookie.getValue();
                     if (logger.isDebugEnabled()) {
-                        logger.debug(cookieKey + ":" + value);
+                        logger.debug("{}:{}", cookieKey, value);
                     }
                     if (StringUtil.isNotEmpty(value)) {
                         parseRoleSet(value, encryptedCookieValue, roleSet);
diff --git a/src/main/java/org/codelibs/fess/helper/SambaHelper.java b/src/main/java/org/codelibs/fess/helper/SambaHelper.java
index 59d0e3ed3..7ee810fe8 100644
--- a/src/main/java/org/codelibs/fess/helper/SambaHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/SambaHelper.java
@@ -51,7 +51,7 @@ public class SambaHelper {
     @PostConstruct
     public void init() {
         if (logger.isDebugEnabled()) {
-            logger.debug("Initialize " + this.getClass().getSimpleName());
+            logger.debug("Initialize {}", this.getClass().getSimpleName());
         }
         fessConfig = ComponentUtil.getFessConfig();
     }
diff --git a/src/main/java/org/codelibs/fess/helper/SearchLogHelper.java b/src/main/java/org/codelibs/fess/helper/SearchLogHelper.java
index 16ac07dbd..68a9f26b1 100644
--- a/src/main/java/org/codelibs/fess/helper/SearchLogHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/SearchLogHelper.java
@@ -77,7 +77,7 @@ public class SearchLogHelper {
     @PostConstruct
     public void init() {
         if (logger.isDebugEnabled()) {
-            logger.debug("Initialize " + this.getClass().getSimpleName());
+            logger.debug("Initialize {}", this.getClass().getSimpleName());
         }
         userInfoCache = CacheBuilder.newBuilder()//
                 .maximumSize(userInfoCacheSize)//
diff --git a/src/main/java/org/codelibs/fess/helper/SuggestHelper.java b/src/main/java/org/codelibs/fess/helper/SuggestHelper.java
index 885d9f28e..b6cab88cd 100644
--- a/src/main/java/org/codelibs/fess/helper/SuggestHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/SuggestHelper.java
@@ -86,7 +86,7 @@ public class SuggestHelper {
     @PostConstruct
     public void init() {
         if (logger.isDebugEnabled()) {
-            logger.debug("Initialize " + this.getClass().getSimpleName());
+            logger.debug("Initialize {}", this.getClass().getSimpleName());
         }
         fessConfig = ComponentUtil.getFessConfig();
         split(fessConfig.getSuggestFieldContents(), ",").of(
diff --git a/src/main/java/org/codelibs/fess/helper/SystemHelper.java b/src/main/java/org/codelibs/fess/helper/SystemHelper.java
index c512bc919..9ea97c85e 100644
--- a/src/main/java/org/codelibs/fess/helper/SystemHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/SystemHelper.java
@@ -108,7 +108,7 @@ public class SystemHelper {
     @PostConstruct
     public void init() {
         if (logger.isDebugEnabled()) {
-            logger.debug("Initialize " + this.getClass().getSimpleName());
+            logger.debug("Initialize {}", this.getClass().getSimpleName());
         }
         updateSystemProperties();
         final FessConfig fessConfig = ComponentUtil.getFessConfig();
@@ -419,7 +419,7 @@ public class SystemHelper {
     protected String createSearchRole(final String type, final String name) {
         final String value = type + ComponentUtil.getFessConfig().getCanonicalLdapName(name);
         if (logger.isDebugEnabled()) {
-            logger.debug("Search Role: " + type + ":" + name + "=" + value);
+            logger.debug("Search Role: {}:{}={}", type, name, value);
         }
         return value;
     }
diff --git a/src/main/java/org/codelibs/fess/helper/ThemeHelper.java b/src/main/java/org/codelibs/fess/helper/ThemeHelper.java
index b84414f3d..0c1a108de 100644
--- a/src/main/java/org/codelibs/fess/helper/ThemeHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/ThemeHelper.java
@@ -112,7 +112,7 @@ public class ThemeHelper {
         try (Stream<Path> walk = Files.walk(dir, FileVisitOption.FOLLOW_LINKS)) {
             walk.sorted(Comparator.reverseOrder()).forEach(f -> {
                 if (logger.isDebugEnabled()) {
-                    logger.debug("Deleting " + f);
+                    logger.debug("Deleting {}", f);
                 }
                 try {
                     Files.delete(f);
diff --git a/src/main/java/org/codelibs/fess/helper/ViewHelper.java b/src/main/java/org/codelibs/fess/helper/ViewHelper.java
index e6d134e1c..0e473a68a 100644
--- a/src/main/java/org/codelibs/fess/helper/ViewHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/ViewHelper.java
@@ -157,7 +157,7 @@ public class ViewHelper {
     @PostConstruct
     public void init() {
         if (logger.isDebugEnabled()) {
-            logger.debug("Initialize " + this.getClass().getSimpleName());
+            logger.debug("Initialize {}", this.getClass().getSimpleName());
         }
         final FessConfig fessConfig = ComponentUtil.getFessConfig();
         escapedHighlightPre = LaFunctions.h(originalHighlightTagPre);
@@ -628,7 +628,7 @@ public class ViewHelper {
 
     public StreamResponse asContentResponse(final Map<String, Object> doc) {
         if (logger.isDebugEnabled()) {
-            logger.debug("writing the content of: " + doc);
+            logger.debug("writing the content of: {}", doc);
         }
         final FessConfig fessConfig = ComponentUtil.getFessConfig();
         final CrawlingConfigHelper crawlingConfigHelper = ComponentUtil.getCrawlingConfigHelper();
@@ -675,7 +675,7 @@ public class ViewHelper {
                 CloseableUtil.closeQuietly(responseData);
             }
             if (logger.isDebugEnabled()) {
-                logger.debug("Finished to write " + url);
+                logger.debug("Finished to write {}", url);
             }
         });
         return response;
@@ -719,7 +719,7 @@ public class ViewHelper {
     protected void writeContentType(final StreamResponse response, final ResponseData responseData) {
         final String mimeType = responseData.getMimeType();
         if (logger.isDebugEnabled()) {
-            logger.debug("mimeType: " + mimeType);
+            logger.debug("mimeType: {}", mimeType);
         }
         if (mimeType == null) {
             response.contentTypeOctetStream();
diff --git a/src/main/java/org/codelibs/fess/helper/WebFsIndexHelper.java b/src/main/java/org/codelibs/fess/helper/WebFsIndexHelper.java
index e54bb83fc..ad895281e 100644
--- a/src/main/java/org/codelibs/fess/helper/WebFsIndexHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/WebFsIndexHelper.java
@@ -193,7 +193,7 @@ public class WebFsIndexHelper {
             }
 
             if (logger.isDebugEnabled()) {
-                logger.debug("Crawling " + urlsStr);
+                logger.debug("Crawling {}", urlsStr);
             }
 
             crawler.setBackground(true);
@@ -326,7 +326,7 @@ public class WebFsIndexHelper {
             }
 
             if (logger.isDebugEnabled()) {
-                logger.debug("Crawling " + pathsStr);
+                logger.debug("Crawling {}", pathsStr);
             }
 
             crawler.setBackground(true);
diff --git a/src/main/java/org/codelibs/fess/indexer/IndexUpdater.java b/src/main/java/org/codelibs/fess/indexer/IndexUpdater.java
index 533a70ebb..7c7adfb6e 100644
--- a/src/main/java/org/codelibs/fess/indexer/IndexUpdater.java
+++ b/src/main/java/org/codelibs/fess/indexer/IndexUpdater.java
@@ -318,7 +318,7 @@ public class IndexUpdater extends Thread {
         final long maxDocumentRequestSize = fessConfig.getIndexerWebfsMaxDocumentRequestSizeAsInteger().longValue();
         for (final EsAccessResult accessResult : arList) {
             if (logger.isDebugEnabled()) {
-                logger.debug("Indexing " + accessResult.getUrl());
+                logger.debug("Indexing {}", accessResult.getUrl());
             }
             accessResult.setStatus(Constants.DONE_STATUS);
             accessResultList.add(accessResult);
@@ -326,7 +326,7 @@ public class IndexUpdater extends Thread {
             if (accessResult.getHttpStatusCode() != 200) {
                 // invalid page
                 if (logger.isDebugEnabled()) {
-                    logger.debug("Skipped. The response code is " + accessResult.getHttpStatusCode() + ".");
+                    logger.debug("Skipped. The response code is {}.", accessResult.getHttpStatusCode());
                 }
                 continue;
             }
@@ -365,8 +365,8 @@ public class IndexUpdater extends Thread {
                     final long processingTime = System.currentTimeMillis() - startTime;
                     docList.addProcessingTime(processingTime);
                     if (logger.isDebugEnabled()) {
-                        logger.debug("Added the document(" + MemoryUtil.byteCountToDisplaySize(docList.getContentSize()) + ", "
-                                + processingTime + "ms). " + "The number of a document cache is " + docList.size() + ".");
+                        logger.debug("Added the document({}, {}ms). " + "The number of a document cache is {}.",
+                                MemoryUtil.byteCountToDisplaySize(docList.getContentSize()), processingTime, docList.size());
                     }
 
                     if (accessResult.getContentLength() == null) {
@@ -379,7 +379,7 @@ public class IndexUpdater extends Thread {
                     }
                     documentSize++;
                     if (logger.isDebugEnabled()) {
-                        logger.debug("The number of an added document is " + documentSize + ".");
+                        logger.debug("The number of an added document is {}.", documentSize);
                     }
                 } catch (final Exception e) {
                     logger.warn("Could not add a doc: " + accessResult.getUrl(), e);
@@ -427,7 +427,7 @@ public class IndexUpdater extends Thread {
         final FessConfig fessConfig = ComponentUtil.getFessConfig();
         map.put(fessConfig.getIndexFieldBoost(), documentBoost);
         if (logger.isDebugEnabled()) {
-            logger.debug("Set a document boost (" + documentBoost + ").");
+            logger.debug("Set a document boost ({}).", documentBoost);
         }
     }
 
@@ -439,7 +439,7 @@ public class IndexUpdater extends Thread {
             final int count = searchLogHelper.getClickCount(url);
             doc.put(fessConfig.getIndexFieldClickCount(), count);
             if (logger.isDebugEnabled()) {
-                logger.debug("Click Count: " + count + ", url: " + url);
+                logger.debug("Click Count: {}, url: {}", count, url);
             }
         }
     }
@@ -452,7 +452,7 @@ public class IndexUpdater extends Thread {
             final long count = searchLogHelper.getFavoriteCount(url);
             map.put(fessConfig.getIndexFieldFavoriteCount(), count);
             if (logger.isDebugEnabled()) {
-                logger.debug("Favorite Count: " + count + ", url: " + url);
+                logger.debug("Favorite Count: {}, url: {}", count, url);
             }
         }
     }
@@ -465,7 +465,7 @@ public class IndexUpdater extends Thread {
             accessResultList.clear();
             final long time = System.currentTimeMillis() - execTime;
             if (logger.isDebugEnabled()) {
-                logger.debug("Updated " + size + " access results. The execution time is " + time + "ms.");
+                logger.debug("Updated {} access results. The execution time is {}ms.", size, time);
             }
             return time;
         }
@@ -523,12 +523,11 @@ public class IndexUpdater extends Thread {
         for (final String sessionId : finishedSessionIdList) {
             final long execTime2 = System.currentTimeMillis();
             if (logger.isDebugEnabled()) {
-                logger.debug("Deleting document data: " + sessionId);
+                logger.debug("Deleting document data: {}", sessionId);
             }
             deleteBySessionId(sessionId);
             if (logger.isDebugEnabled()) {
-                logger.debug("Deleted " + sessionId + " documents. The execution time is " + (System.currentTimeMillis() - execTime2)
-                        + "ms.");
+                logger.debug("Deleted {} documents. The execution time is {}ms.", sessionId, (System.currentTimeMillis() - execTime2));
             }
         }
         finishedSessionIdList.clear();
diff --git a/src/main/java/org/codelibs/fess/job/CrawlJob.java b/src/main/java/org/codelibs/fess/job/CrawlJob.java
index cc1fbb433..a0d52df34 100644
--- a/src/main/java/org/codelibs/fess/job/CrawlJob.java
+++ b/src/main/java/org/codelibs/fess/job/CrawlJob.java
@@ -183,11 +183,11 @@ public class CrawlJob extends ExecJob {
             if (fessConfig.isSchedulerTarget(scheduledJob.getTarget())) {
                 if (scheduledJob.isRunning()) {
                     if (logger.isDebugEnabled()) {
-                        logger.debug(scheduledJob.getId() + " is running.");
+                        logger.debug("{} is running.", scheduledJob.getId());
                     }
                     counter.incrementAndGet();
                 } else if (logger.isDebugEnabled()) {
-                    logger.debug(scheduledJob.getId() + " is not running.");
+                    logger.debug("{} is not running.", scheduledJob.getId());
                 }
             }
         });
diff --git a/src/main/java/org/codelibs/fess/ldap/LdapManager.java b/src/main/java/org/codelibs/fess/ldap/LdapManager.java
index 08cb99c5a..25953be20 100644
--- a/src/main/java/org/codelibs/fess/ldap/LdapManager.java
+++ b/src/main/java/org/codelibs/fess/ldap/LdapManager.java
@@ -72,7 +72,7 @@ public class LdapManager {
     @PostConstruct
     public void init() {
         if (logger.isDebugEnabled()) {
-            logger.debug("Initialize " + this.getClass().getSimpleName());
+            logger.debug("Initialize {}", this.getClass().getSimpleName());
         }
         fessConfig = ComponentUtil.getFessConfig();
     }
@@ -198,7 +198,7 @@ public class LdapManager {
         // AD: (&(objectClass=user)(sAMAccountName=%s))
         final String filter = String.format(accountFilter, ldapUser.getName());
         if (logger.isDebugEnabled()) {
-            logger.debug("Account Filter: " + filter);
+            logger.debug("Account Filter: {}", filter);
         }
         search(bindDn, filter, new String[] { fessConfig.getLdapMemberofAttribute() }, () -> ldapUser.getEnvironment(), result -> {
             processSearchRoles(result, entryDn -> {
@@ -211,7 +211,7 @@ public class LdapManager {
         });
 
         if (logger.isDebugEnabled()) {
-            logger.debug("role: " + roleSet);
+            logger.debug("role: {}", roleSet);
         }
         return roleSet.toArray(new String[roleSet.size()]);
     }
@@ -221,13 +221,13 @@ public class LdapManager {
         // (member:1.2.840.113556.1.4.1941:=%s)
         final String filter = String.format(groupFilter, dn);
         if (logger.isDebugEnabled()) {
-            logger.debug("Group Filter: " + filter);
+            logger.debug("Group Filter: {}", filter);
         }
         search(bindDn, filter, null, () -> ldapUser.getEnvironment(), result -> {
             for (final SearchResult srcrslt : result) {
                 final String groupDn = srcrslt.getNameInNamespace();
                 if (logger.isDebugEnabled()) {
-                    logger.debug("groupDn: " + groupDn);
+                    logger.debug("groupDn: {}", groupDn);
                 }
                 updateSearchRoles(roleSet, groupDn);
             }
@@ -276,7 +276,7 @@ public class LdapManager {
                     final String entryDn = attrValue.toString();
 
                     if (logger.isDebugEnabled()) {
-                        logger.debug("entryDn: " + entryDn);
+                        logger.debug("entryDn: {}", entryDn);
                     }
                     consumer.accept(entryDn);
                 }
diff --git a/src/main/java/org/codelibs/fess/mylasta/direction/sponsor/FessUserLocaleProcessProvider.java b/src/main/java/org/codelibs/fess/mylasta/direction/sponsor/FessUserLocaleProcessProvider.java
index 4ed0c5307..9bb016277 100644
--- a/src/main/java/org/codelibs/fess/mylasta/direction/sponsor/FessUserLocaleProcessProvider.java
+++ b/src/main/java/org/codelibs/fess/mylasta/direction/sponsor/FessUserLocaleProcessProvider.java
@@ -49,7 +49,7 @@ public class FessUserLocaleProcessProvider implements UserLocaleProcessProvider
             try {
                 return requestManager.getParameter(name).filter(StringUtil::isNotBlank).map(LocaleUtils::toLocale);
             } catch (final Exception e) {
-                logger.debug("Failed to parse a value of " + name + ".", e);
+                logger.debug("Failed to parse a value of {}.", name, e);
             }
         }
         return OptionalObject.empty();
diff --git a/src/main/java/org/codelibs/fess/score/GoogleAnalyticsScoreBooster.java b/src/main/java/org/codelibs/fess/score/GoogleAnalyticsScoreBooster.java
index 652d71780..c7b14e356 100644
--- a/src/main/java/org/codelibs/fess/score/GoogleAnalyticsScoreBooster.java
+++ b/src/main/java/org/codelibs/fess/score/GoogleAnalyticsScoreBooster.java
@@ -68,7 +68,7 @@ public class GoogleAnalyticsScoreBooster extends ScoreBooster {
     @PostConstruct
     public void init() {
         if (logger.isDebugEnabled()) {
-            logger.debug("Initialize " + this.getClass().getSimpleName());
+            logger.debug("Initialize {}", this.getClass().getSimpleName());
         }
         if (!Paths.get(keyFileLocation).toFile().exists()) {
             logger.info("GA Key File does not exist.");
diff --git a/src/main/java/org/codelibs/fess/sso/aad/AzureAdAuthenticator.java b/src/main/java/org/codelibs/fess/sso/aad/AzureAdAuthenticator.java
index 1cba72624..17202b026 100644
--- a/src/main/java/org/codelibs/fess/sso/aad/AzureAdAuthenticator.java
+++ b/src/main/java/org/codelibs/fess/sso/aad/AzureAdAuthenticator.java
@@ -114,7 +114,7 @@ public class AzureAdAuthenticator implements SsoAuthenticator {
     @PostConstruct
     public void init() {
         if (logger.isDebugEnabled()) {
-            logger.debug("Initialize " + this.getClass().getSimpleName());
+            logger.debug("Initialize {}", this.getClass().getSimpleName());
         }
         ComponentUtil.getSsoManager().register(this);
         groupCache = CacheBuilder.newBuilder().expireAfterWrite(groupCacheExpiry, TimeUnit.SECONDS).build();
diff --git a/src/main/java/org/codelibs/fess/sso/oic/OpenIdConnectAuthenticator.java b/src/main/java/org/codelibs/fess/sso/oic/OpenIdConnectAuthenticator.java
index 79ed0ee36..29c0702db 100644
--- a/src/main/java/org/codelibs/fess/sso/oic/OpenIdConnectAuthenticator.java
+++ b/src/main/java/org/codelibs/fess/sso/oic/OpenIdConnectAuthenticator.java
@@ -76,7 +76,7 @@ public class OpenIdConnectAuthenticator implements SsoAuthenticator {
     @PostConstruct
     public void init() {
         if (logger.isDebugEnabled()) {
-            logger.debug("Initialize " + this.getClass().getSimpleName());
+            logger.debug("Initialize {}", this.getClass().getSimpleName());
         }
         ComponentUtil.getSsoManager().register(this);
     }
diff --git a/src/main/java/org/codelibs/fess/sso/spnego/SpnegoAuthenticator.java b/src/main/java/org/codelibs/fess/sso/spnego/SpnegoAuthenticator.java
index 44acbf8d4..ca671ef46 100644
--- a/src/main/java/org/codelibs/fess/sso/spnego/SpnegoAuthenticator.java
+++ b/src/main/java/org/codelibs/fess/sso/spnego/SpnegoAuthenticator.java
@@ -70,7 +70,7 @@ public class SpnegoAuthenticator implements SsoAuthenticator {
     @PostConstruct
     public void init() {
         if (logger.isDebugEnabled()) {
-            logger.debug("Initialize " + this.getClass().getSimpleName());
+            logger.debug("Initialize {}", this.getClass().getSimpleName());
         }
         ComponentUtil.getSsoManager().register(this);
     }
@@ -146,7 +146,7 @@ public class SpnegoAuthenticator implements SsoAuthenticator {
                     }
 
                     if (logger.isDebugEnabled()) {
-                        logger.debug("principal=" + principal);
+                        logger.debug("principal={}", principal);
                     }
 
                     final String[] username = principal.getName().split("@", 2);
diff --git a/src/main/java/org/codelibs/fess/taglib/FessFunctions.java b/src/main/java/org/codelibs/fess/taglib/FessFunctions.java
index add1bd9e6..138585bdd 100644
--- a/src/main/java/org/codelibs/fess/taglib/FessFunctions.java
+++ b/src/main/java/org/codelibs/fess/taglib/FessFunctions.java
@@ -82,7 +82,7 @@ public class FessFunctions {
                             return Files.getLastModifiedTime(path).toMillis();
                         }
                     } catch (final Exception e) {
-                        logger.debug("Failed to access " + key, e);
+                        logger.debug("Failed to access {}", key, e);
                     }
                     return 0L;
                 }
@@ -328,7 +328,7 @@ public class FessFunctions {
                     sb.append("?t=").append(value.toString());
                 }
             } catch (final ExecutionException e) {
-                logger.debug("Failed to access " + input, e);
+                logger.debug("Failed to access {}", input, e);
             }
         }
         return LaResponseUtil.getResponse().encodeURL(sb.toString());
diff --git a/src/main/java/org/codelibs/fess/thumbnail/ThumbnailManager.java b/src/main/java/org/codelibs/fess/thumbnail/ThumbnailManager.java
index 6705e05d0..a7a9f1063 100644
--- a/src/main/java/org/codelibs/fess/thumbnail/ThumbnailManager.java
+++ b/src/main/java/org/codelibs/fess/thumbnail/ThumbnailManager.java
@@ -89,7 +89,7 @@ public class ThumbnailManager {
     @PostConstruct
     public void init() {
         if (logger.isDebugEnabled()) {
-            logger.debug("Initialize " + this.getClass().getSimpleName());
+            logger.debug("Initialize {}", this.getClass().getSimpleName());
         }
         final String thumbnailPath = System.getProperty(Constants.FESS_THUMBNAIL_PATH);
         if (thumbnailPath != null) {
@@ -110,7 +110,7 @@ public class ThumbnailManager {
         }
 
         if (logger.isDebugEnabled()) {
-            logger.debug("Thumbnail Directory: " + baseDir.getAbsolutePath());
+            logger.debug("Thumbnail Directory: {}", baseDir.getAbsolutePath());
         }
 
         thumbnailTaskQueue = new LinkedBlockingQueue<>(thumbnailTaskQueueSize);
@@ -188,7 +188,7 @@ public class ThumbnailManager {
         });
         taskList.clear();
         if (logger.isDebugEnabled()) {
-            logger.debug("Storing " + list.size() + " thumbnail tasks.");
+            logger.debug("Storing {} thumbnail tasks.", list.size());
         }
         final ThumbnailQueueBhv thumbnailQueueBhv = ComponentUtil.getComponent(ThumbnailQueueBhv.class);
         thumbnailQueueBhv.batchInsert(list);
@@ -210,7 +210,7 @@ public class ThumbnailManager {
             idList.add(entity.getId());
             if (cleanup) {
                 if (logger.isDebugEnabled()) {
-                    logger.debug("Removing thumbnail queue: " + entity);
+                    logger.debug("Removing thumbnail queue: {}", entity);
                 }
                 return null;
             } else {
@@ -235,7 +235,7 @@ public class ThumbnailManager {
 
     protected void process(final FessConfig fessConfig, final ThumbnailQueue entity) {
         if (logger.isDebugEnabled()) {
-            logger.debug("Processing thumbnail: " + entity);
+            logger.debug("Processing thumbnail: {}", entity);
         }
         final String generatorName = entity.getGenerator();
         try {
@@ -259,7 +259,7 @@ public class ThumbnailManager {
                     logger.warn(generatorName + " is not available.");
                 }
             } else if (logger.isDebugEnabled()) {
-                logger.debug("No image file exists: " + noImageFile.getAbsolutePath());
+                logger.debug("No image file exists: {}", noImageFile.getAbsolutePath());
             }
         } catch (final Exception e) {
             logger.warn("Failed to create thumbnail for " + entity, e);
@@ -273,7 +273,7 @@ public class ThumbnailManager {
                 final Tuple3<String, String, String> task = generator.createTask(path, docMap);
                 if (task != null) {
                     if (logger.isDebugEnabled()) {
-                        logger.debug("Add thumbnail task: " + task);
+                        logger.debug("Add thumbnail task: {}", task);
                     }
                     if (!thumbnailTaskQueue.offer(task)) {
                         logger.warn("Failed to add thumbnail task: " + task);
@@ -284,7 +284,7 @@ public class ThumbnailManager {
             }
         }
         if (logger.isDebugEnabled()) {
-            logger.debug("Thumbnail generator is not found: " + (docMap != null ? docMap.get("url") : docMap));
+            logger.debug("Thumbnail generator is not found: {}", (docMap != null ? docMap.get("url") : docMap));
         }
         return false;
     }
@@ -320,7 +320,7 @@ public class ThumbnailManager {
 
     public void add(final ThumbnailGenerator generator) {
         if (logger.isDebugEnabled()) {
-            logger.debug(generator.getName() + " is available.");
+            logger.debug("{} is available.", generator.getName());
         }
         if (generator.isAvailable()) {
             generatorList.add(generator);
@@ -393,7 +393,7 @@ public class ThumbnailManager {
                     if (docId != null) {
                         deleteFileMap.remove(docId);
                         if (logger.isDebugEnabled()) {
-                            logger.debug("Keep thumbnail: " + docId);
+                            logger.debug("Keep thumbnail: {}", docId);
                         }
                     }
                 });
@@ -407,7 +407,7 @@ public class ThumbnailManager {
             try {
                 Files.delete(path);
                 if (logger.isDebugEnabled()) {
-                    logger.debug("Delete " + path);
+                    logger.debug("Delete {}", path);
                 }
 
                 Path parent = path.getParent();
@@ -424,7 +424,7 @@ public class ThumbnailManager {
             final String b = basePath.toUri().toString();
             final String id = s.replace(b, StringUtil.EMPTY).replace("." + imageExtention, StringUtil.EMPTY).replace("/", StringUtil.EMPTY);
             if (logger.isDebugEnabled()) {
-                logger.debug("Base: " + b + " File: " + s + " DocId: " + id);
+                logger.debug("Base: {} File: {} DocId: {}", b, s, id);
             }
             return id;
         }
@@ -477,7 +477,7 @@ public class ThumbnailManager {
             if (directory.list() != null && directory.list().length == 0 && !THUMBNAILS_DIR_NAME.equals(directory.getName())) {
                 Files.delete(dir);
                 if (logger.isDebugEnabled()) {
-                    logger.debug("Delete " + dir);
+                    logger.debug("Delete {}", dir);
                 }
                 return true;
             }
diff --git a/src/main/java/org/codelibs/fess/thumbnail/impl/BaseThumbnailGenerator.java b/src/main/java/org/codelibs/fess/thumbnail/impl/BaseThumbnailGenerator.java
index d2d01f342..d48964731 100644
--- a/src/main/java/org/codelibs/fess/thumbnail/impl/BaseThumbnailGenerator.java
+++ b/src/main/java/org/codelibs/fess/thumbnail/impl/BaseThumbnailGenerator.java
@@ -131,7 +131,7 @@ public abstract class BaseThumbnailGenerator implements ThumbnailGenerator {
         final String thumbnailId = DocumentUtil.getValue(docMap, fessConfig.getIndexFieldId(), String.class);
         final Tuple3<String, String, String> task = new Tuple3<>(getName(), thumbnailId, path);
         if (logger.isDebugEnabled()) {
-            logger.debug("Create thumbnail task: " + task);
+            logger.debug("Create thumbnail task: {}", task);
         }
         return task;
     }
diff --git a/src/main/java/org/codelibs/fess/thumbnail/impl/CommandGenerator.java b/src/main/java/org/codelibs/fess/thumbnail/impl/CommandGenerator.java
index 3f4885a2f..978878948 100644
--- a/src/main/java/org/codelibs/fess/thumbnail/impl/CommandGenerator.java
+++ b/src/main/java/org/codelibs/fess/thumbnail/impl/CommandGenerator.java
@@ -50,7 +50,7 @@ public class CommandGenerator extends BaseThumbnailGenerator {
     @PostConstruct
     public void init() {
         if (logger.isDebugEnabled()) {
-            logger.debug("Initialize " + this.getClass().getSimpleName());
+            logger.debug("Initialize {}", this.getClass().getSimpleName());
         }
         if (baseDir == null) {
             baseDir = new File(System.getProperty("java.io.tmpdir"));
@@ -67,12 +67,12 @@ public class CommandGenerator extends BaseThumbnailGenerator {
     @Override
     public boolean generate(final String thumbnailId, final File outputFile) {
         if (logger.isDebugEnabled()) {
-            logger.debug("Generate Thumbnail: " + thumbnailId);
+            logger.debug("Generate Thumbnail: {}", thumbnailId);
         }
 
         if (outputFile.exists()) {
             if (logger.isDebugEnabled()) {
-                logger.debug("The thumbnail file exists: " + outputFile.getAbsolutePath());
+                logger.debug("The thumbnail file exists: {}", outputFile.getAbsolutePath());
             }
             return true;
         }
@@ -110,7 +110,7 @@ public class CommandGenerator extends BaseThumbnailGenerator {
                 }
 
                 if (logger.isDebugEnabled()) {
-                    logger.debug("Thumbnail File: " + outputPath);
+                    logger.debug("Thumbnail File: {}", outputPath);
                 }
                 return true;
             } catch (final Exception e) {
@@ -119,7 +119,7 @@ public class CommandGenerator extends BaseThumbnailGenerator {
                 return false;
             } finally {
                 if (tempFile != null && !tempFile.delete()) {
-                    logger.debug("Failed to delete " + tempFile.getAbsolutePath());
+                    logger.debug("Failed to delete {}", tempFile.getAbsolutePath());
                 }
             }
         });
@@ -131,7 +131,7 @@ public class CommandGenerator extends BaseThumbnailGenerator {
         Process p = null;
 
         if (logger.isDebugEnabled()) {
-            logger.debug("Thumbnail Command: " + cmdList);
+            logger.debug("Thumbnail Command: {}", cmdList);
         }
 
         TimerTask task = null;
diff --git a/src/main/java/org/codelibs/fess/thumbnail/impl/HtmlTagBasedGenerator.java b/src/main/java/org/codelibs/fess/thumbnail/impl/HtmlTagBasedGenerator.java
index e88659e55..27ef412d7 100644
--- a/src/main/java/org/codelibs/fess/thumbnail/impl/HtmlTagBasedGenerator.java
+++ b/src/main/java/org/codelibs/fess/thumbnail/impl/HtmlTagBasedGenerator.java
@@ -51,7 +51,7 @@ public class HtmlTagBasedGenerator extends BaseThumbnailGenerator {
         final String thumbnailId = DocumentUtil.getValue(docMap, fessConfig.getIndexFieldId(), String.class);
         final Tuple3<String, String, String> task = new Tuple3<>(getName(), thumbnailId, path);
         if (logger.isDebugEnabled()) {
-            logger.debug("Create thumbnail task: " + task);
+            logger.debug("Create thumbnail task: {}", task);
         }
         return task;
     }
@@ -59,12 +59,12 @@ public class HtmlTagBasedGenerator extends BaseThumbnailGenerator {
     @Override
     public boolean generate(final String thumbnailId, final File outputFile) {
         if (logger.isDebugEnabled()) {
-            logger.debug("Generate Thumbnail: " + thumbnailId);
+            logger.debug("Generate Thumbnail: {}", thumbnailId);
         }
 
         if (outputFile.exists()) {
             if (logger.isDebugEnabled()) {
-                logger.debug("The thumbnail file exists: " + outputFile.getAbsolutePath());
+                logger.debug("The thumbnail file exists: {}", outputFile.getAbsolutePath());
             }
             return true;
         }
@@ -83,7 +83,7 @@ public class HtmlTagBasedGenerator extends BaseThumbnailGenerator {
                 responseData -> {
                     if (!isImageMimeType(responseData)) {
                         if (logger.isDebugEnabled()) {
-                            logger.debug("Thumbnail is not image: " + thumbnailId + " : " + responseData.getUrl());
+                            logger.debug("Thumbnail is not image: {} : {}", thumbnailId, responseData.getUrl());
                         }
                         updateThumbnailField(thumbnailId, StringUtil.EMPTY);
                         return false;
@@ -102,7 +102,7 @@ public class HtmlTagBasedGenerator extends BaseThumbnailGenerator {
                             break;
                         case NO_IMAGE:
                             if (logger.isDebugEnabled()) {
-                                logger.debug("No thumbnail: " + thumbnailId + " -> " + responseData.getUrl());
+                                logger.debug("No thumbnail: {} -> {}", thumbnailId, responseData.getUrl());
                             }
                             break;
                         default:
diff --git a/src/main/java/org/codelibs/fess/util/GsaConfigParser.java b/src/main/java/org/codelibs/fess/util/GsaConfigParser.java
index 879f50d2c..c8d3e8f60 100644
--- a/src/main/java/org/codelibs/fess/util/GsaConfigParser.java
+++ b/src/main/java/org/codelibs/fess/util/GsaConfigParser.java
@@ -115,7 +115,7 @@ public class GsaConfigParser extends DefaultHandler {
     @Override
     public void startElement(final String uri, final String localName, final String qName, final Attributes attributes) throws SAXException {
         if (logger.isDebugEnabled()) {
-            logger.debug("Start Element: " + qName);
+            logger.debug("Start Element: {}", qName);
         }
         if (tagQueue.isEmpty() && !"eef".equalsIgnoreCase(qName)) {
             throw new GsaConfigException("Invalid format.");
@@ -137,7 +137,7 @@ public class GsaConfigParser extends DefaultHandler {
     @Override
     public void endElement(final String uri, final String localName, final String qName) throws SAXException {
         if (logger.isDebugEnabled()) {
-            logger.debug("End Element: " + qName);
+            logger.debug("End Element: {}", qName);
         }
         if (GOOD_URLS.equalsIgnoreCase(qName)) {
             if (labelType != null) {
@@ -224,7 +224,7 @@ public class GsaConfigParser extends DefaultHandler {
     public void characters(final char[] ch, final int start, final int length) throws SAXException {
         final String text = new String(ch, start, length);
         if (logger.isDebugEnabled()) {
-            logger.debug("Text: " + text);
+            logger.debug("Text: {}", text);
         }
         textBuf.append(text);
     }
diff --git a/src/main/java/org/codelibs/fess/util/QueryResponseList.java b/src/main/java/org/codelibs/fess/util/QueryResponseList.java
index cfa11edbb..ba1e6d0bf 100644
--- a/src/main/java/org/codelibs/fess/util/QueryResponseList.java
+++ b/src/main/java/org/codelibs/fess/util/QueryResponseList.java
@@ -177,7 +177,7 @@ public class QueryResponseList implements List<Map<String, Object>> {
             }
         } catch (final Exception e) {
             if (logger.isDebugEnabled()) {
-                logger.debug("Could not create a highlighting value: " + docMap, e);
+                logger.debug("Could not create a highlighting value: {}", docMap, e);
             }
         }
 
diff --git a/src/main/java/org/codelibs/fess/util/UpgradeUtil.java b/src/main/java/org/codelibs/fess/util/UpgradeUtil.java
index aa0f8ca3d..b386ad7a1 100644
--- a/src/main/java/org/codelibs/fess/util/UpgradeUtil.java
+++ b/src/main/java/org/codelibs/fess/util/UpgradeUtil.java
@@ -77,7 +77,7 @@ public final class UpgradeUtil {
                     logger.info("Created " + aliasName + " alias for " + indexName);
                     return true;
                 } else if (logger.isDebugEnabled()) {
-                    logger.debug("Failed to create " + aliasName + " alias for " + indexName);
+                    logger.debug("Failed to create {} alias for {}", aliasName, indexName);
                 }
             }
         } catch (final ResourceNotFoundRuntimeException e) {
diff --git a/src/test/java/org/codelibs/fess/thumbnail/impl/HtmlTagBasedGeneratorTest.java b/src/test/java/org/codelibs/fess/thumbnail/impl/HtmlTagBasedGeneratorTest.java
index ea1cec4ec..a505b9692 100644
--- a/src/test/java/org/codelibs/fess/thumbnail/impl/HtmlTagBasedGeneratorTest.java
+++ b/src/test/java/org/codelibs/fess/thumbnail/impl/HtmlTagBasedGeneratorTest.java
@@ -92,7 +92,7 @@ public class HtmlTagBasedGeneratorTest extends UnitFessTestCase {
 
     private void assertImageSize(File file, int width, int height) throws IOException {
         BufferedImage img = ImageIO.read(file);
-        logger.debug("width: " + img.getWidth() + ", height: " + img.getHeight());
+        logger.debug("width: {}, height: {}", img.getWidth(), img.getHeight());
         assertEquals("Image Width", width, img.getWidth());
         assertEquals("Image Height", height, img.getHeight());
     }