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 c60b7e12f..d7e6cd717 100644
--- a/src/main/java/org/codelibs/fess/app/job/ScriptExecutorJob.java
+++ b/src/main/java/org/codelibs/fess/app/job/ScriptExecutorJob.java
@@ -119,7 +119,7 @@ public class ScriptExecutorJob implements LaJob {
                 try {
                     task.stop();
                 } catch (final Exception e) {
-                    logger.warn("Failed to stop " + jobLog, e);
+                    logger.warn("Failed to stop {}", jobLog, e);
                 }
             }
             jobLog.setEndTime(ComponentUtil.getSystemHelper().getCurrentTimeAsLong());
diff --git a/src/main/java/org/codelibs/fess/app/web/admin/esreq/AdminEsreqAction.java b/src/main/java/org/codelibs/fess/app/web/admin/esreq/AdminEsreqAction.java
index 1649e31c0..a502423e5 100644
--- a/src/main/java/org/codelibs/fess/app/web/admin/esreq/AdminEsreqAction.java
+++ b/src/main/java/org/codelibs/fess/app/web/admin/esreq/AdminEsreqAction.java
@@ -114,7 +114,7 @@ public class AdminEsreqAction extends FessAdminAction {
                     }
                 });
             } catch (final Exception e) {
-                logger.warn("Failed to process request file: " + form.requestFile.getFileName(), e);
+                logger.warn("Failed to process request file: {}", form.requestFile.getFileName(), e);
                 throwValidationError(messages -> messages.addErrorsInvalidHeaderForRequestFile(GLOBAL, e.getMessage()),
                         () -> asListHtml(this::saveToken));
             }
diff --git a/src/main/java/org/codelibs/fess/app/web/admin/storage/AdminStorageAction.java b/src/main/java/org/codelibs/fess/app/web/admin/storage/AdminStorageAction.java
index b5e5a5281..5ccc7e867 100644
--- a/src/main/java/org/codelibs/fess/app/web/admin/storage/AdminStorageAction.java
+++ b/src/main/java/org/codelibs/fess/app/web/admin/storage/AdminStorageAction.java
@@ -241,7 +241,7 @@ public class AdminStorageAction extends FessAdminAction {
                     minioClient.makeBucket(args);
                     logger.info("Created bucket: {}", fessConfig.getStorageBucket());
                 } catch (final Exception e1) {
-                    logger.warn("Failed to create bucket:" + fessConfig.getStorageBucket(), e1);
+                    logger.warn("Failed to create bucket: {}", fessConfig.getStorageBucket(), e1);
                 }
             } else if (logger.isDebugEnabled()) {
                 logger.debug("Failed to access {}", fessConfig.getStorageEndpoint(), e);
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 849b2207f..426158029 100644
--- a/src/main/java/org/codelibs/fess/crawler/transformer/FessXpathTransformer.java
+++ b/src/main/java/org/codelibs/fess/crawler/transformer/FessXpathTransformer.java
@@ -182,7 +182,7 @@ public class FessXpathTransformer extends XpathTransformer implements FessTransf
                     break;
                 }
             } catch (final TransformerException e) {
-                logger.warn("Could not parse a value of " + entry.getKey() + ":" + entry.getValue(), e);
+                logger.warn("Could not parse a value of {}:{}", entry.getKey(), entry.getValue(), e);
             }
         }
 
@@ -247,7 +247,7 @@ public class FessXpathTransformer extends XpathTransformer implements FessTransf
                 }
             }
         } catch (final TransformerException e) {
-            logger.warn("Could not parse a value of " + META_NAME_ROBOTS_CONTENT, e);
+            logger.warn("Could not parse a value of {}", META_NAME_ROBOTS_CONTENT, e);
         }
 
     }
@@ -408,7 +408,7 @@ public class FessXpathTransformer extends XpathTransformer implements FessTransf
                     putResultDataBody(dataMap, fessConfig.getIndexFieldCache(), new String(InputStreamUtil.getBytes(is), charSet));
                     putResultDataBody(dataMap, fessConfig.getIndexFieldHasCache(), Constants.TRUE);
                 } catch (final Exception e) {
-                    logger.warn("Failed to write a cache: " + sessionId + ":" + responseData, e);
+                    logger.warn("Failed to write a cache: {}:{}", sessionId, responseData, e);
                 }
             } else {
                 logger.debug("Content size is too large({} > {}): {}", responseData.getContentLength(),
@@ -547,7 +547,7 @@ public class FessXpathTransformer extends XpathTransformer implements FessTransf
             final URL u = new URL(baseUrl);
             return new URL(u, canonicalUrl.startsWith(":") ? u.getProtocol() + canonicalUrl : canonicalUrl).toString();
         } catch (final MalformedURLException e) {
-            logger.warn("Invalid canonical url: " + baseUrl + " : " + canonicalUrl, e);
+            logger.warn("Invalid canonical url: {} : {}", baseUrl, canonicalUrl, e);
         }
         return null;
     }
@@ -694,7 +694,7 @@ public class FessXpathTransformer extends XpathTransformer implements FessTransf
                 buf.append("\n");
             }
         } catch (final Exception e) {
-            logger.warn("Could not parse a value of " + xpath, e);
+            logger.warn("Could not parse a value of {}", xpath, e);
         }
         return buf.toString().trim();
     }
@@ -865,7 +865,7 @@ public class FessXpathTransformer extends XpathTransformer implements FessTransf
                 return firstThumbnailUrl;
             }
         } catch (final Exception e) {
-            logger.warn("Failed to retrieve thumbnail url from " + responseData.getUrl(), e);
+            logger.warn("Failed to retrieve thumbnail url from {}", responseData.getUrl(), e);
         }
         return null;
     }
diff --git a/src/main/java/org/codelibs/fess/dict/DictionaryManager.java b/src/main/java/org/codelibs/fess/dict/DictionaryManager.java
index 4c3a34064..6a366cc9b 100644
--- a/src/main/java/org/codelibs/fess/dict/DictionaryManager.java
+++ b/src/main/java/org/codelibs/fess/dict/DictionaryManager.java
@@ -67,7 +67,7 @@ public class DictionaryManager {
                         }
                     }
                 } catch (final Exception e) {
-                    logger.warn("Failed to load " + fileMap, e);
+                    logger.warn("Failed to load {}", fileMap, e);
                 }
                 return null;
             }).filter(file -> file != null).toArray(n -> new DictionaryFile<?>[n]);
diff --git a/src/main/java/org/codelibs/fess/ds/DataStoreFactory.java b/src/main/java/org/codelibs/fess/ds/DataStoreFactory.java
index 83cde864a..f3c8bdfda 100644
--- a/src/main/java/org/codelibs/fess/ds/DataStoreFactory.java
+++ b/src/main/java/org/codelibs/fess/ds/DataStoreFactory.java
@@ -110,7 +110,7 @@ public class DataStoreFactory {
                     }
                 }
             } catch (final Exception e) {
-                logger.warn("Failed to load " + jarFile.getAbsolutePath(), e);
+                logger.warn("Failed to load {}", jarFile.getAbsolutePath(), e);
             }
         }
         return nameSet.stream().sorted().collect(Collectors.toList());
diff --git a/src/main/java/org/codelibs/fess/helper/CrawlingConfigHelper.java b/src/main/java/org/codelibs/fess/helper/CrawlingConfigHelper.java
index 2f6151fd2..376fa54e8 100644
--- a/src/main/java/org/codelibs/fess/helper/CrawlingConfigHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/CrawlingConfigHelper.java
@@ -120,7 +120,7 @@ public class CrawlingConfigHelper {
                 }
             });
         } catch (final ExecutionException e) {
-            logger.warn("Failed to access a crawling config cache: " + configId, e);
+            logger.warn("Failed to access a crawling config cache: {}", configId, e);
             return null;
         }
     }
diff --git a/src/main/java/org/codelibs/fess/helper/DataIndexHelper.java b/src/main/java/org/codelibs/fess/helper/DataIndexHelper.java
index 6e9a33494..b30ff1767 100644
--- a/src/main/java/org/codelibs/fess/helper/DataIndexHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/DataIndexHelper.java
@@ -215,7 +215,7 @@ public class DataIndexHelper {
                 try {
                     dataStore.store(dataConfig, indexUpdateCallback, initParamMap);
                 } catch (final Throwable e) {
-                    logger.error("Failed to process a data crawling: " + dataConfig.getName(), e);
+                    logger.error("Failed to process a data crawling: {}", dataConfig.getName(), e);
                     ComponentUtil.getComponent(FailureUrlService.class).store(dataConfig, e.getClass().getCanonicalName(),
                             dataConfig.getConfigId() + ":" + dataConfig.getName(), e);
                 } finally {
@@ -247,7 +247,7 @@ public class DataIndexHelper {
                 final long numOfDeleted = fessEsClient.deleteByQuery(index, queryBuilder);
                 logger.info("Deleted {} old docs.", numOfDeleted);
             } catch (final Exception e) {
-                logger.error("Could not delete old docs at " + dataConfig, e);
+                logger.error("Could not delete old docs at {}", dataConfig, e);
             }
         }
 
diff --git a/src/main/java/org/codelibs/fess/helper/DocumentHelper.java b/src/main/java/org/codelibs/fess/helper/DocumentHelper.java
index d5e4dbc60..b8b580483 100644
--- a/src/main/java/org/codelibs/fess/helper/DocumentHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/DocumentHelper.java
@@ -248,7 +248,7 @@ public class DocumentHelper {
                 }
                 return SIMILAR_DOC_HASH_PREFIX + Base64.getUrlEncoder().withoutPadding().encodeToString(baos.toByteArray());
             } catch (final IOException e) {
-                logger.warn("Failed to encode " + hash, e);
+                logger.warn("Failed to encode {}", hash, e);
             }
         }
         return hash;
diff --git a/src/main/java/org/codelibs/fess/helper/LabelTypeHelper.java b/src/main/java/org/codelibs/fess/helper/LabelTypeHelper.java
index 6d7ecbb7d..c2f44fd80 100644
--- a/src/main/java/org/codelibs/fess/helper/LabelTypeHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/LabelTypeHelper.java
@@ -152,8 +152,8 @@ public class LabelTypeHelper {
                 try {
                     list.add(new LabelTypePattern(labelType.getValue(), includedPaths, excludedPaths));
                 } catch (final Exception e) {
-                    logger.warn("Failed to create a matching pattern of a label: " + labelType.getValue() + ", includedPaths:"
-                            + includedPaths + ", excludedPaths:" + excludedPaths, e);
+                    logger.warn("Failed to create a matching pattern of a label: {}, includedPaths:{}, excludedPaths:{}",
+                            labelType.getValue(), includedPaths, excludedPaths, e);
                 }
             }
         }
diff --git a/src/main/java/org/codelibs/fess/helper/PluginHelper.java b/src/main/java/org/codelibs/fess/helper/PluginHelper.java
index 10b740fb7..2139a6049 100644
--- a/src/main/java/org/codelibs/fess/helper/PluginHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/PluginHelper.java
@@ -146,7 +146,7 @@ public class PluginHelper {
                     }
                 }
             } catch (final Exception e) {
-                logger.warn("Failed to parse " + pluginUrl + "maven-metadata.xml.", e);
+                logger.warn("Failed to parse {}maven-metadata.xml.", pluginUrl, e);
             }
         }
         return list;
diff --git a/src/main/java/org/codelibs/fess/helper/SuggestHelper.java b/src/main/java/org/codelibs/fess/helper/SuggestHelper.java
index a7d1ecc35..86fbd3404 100644
--- a/src/main/java/org/codelibs/fess/helper/SuggestHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/SuggestHelper.java
@@ -111,7 +111,7 @@ public class SuggestHelper {
             try {
                 suggester.settings().array().add(SuggestSettings.DefaultKeys.SUPPORTED_FIELDS, field);
             } catch (final SuggestSettingsException e) {
-                logger.warn("Failed to add " + field, e);
+                logger.warn("Failed to add {}", field, e);
             }
         }));
         suggester.createIndexIfNothing();
diff --git a/src/main/java/org/codelibs/fess/helper/SystemHelper.java b/src/main/java/org/codelibs/fess/helper/SystemHelper.java
index 63780d7b2..1da1acf8a 100644
--- a/src/main/java/org/codelibs/fess/helper/SystemHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/SystemHelper.java
@@ -331,8 +331,7 @@ public class SystemHelper {
                             try {
                                 Files.copy(baseJspFile.toPath(), jspFile.toPath());
                             } catch (final IOException ex) {
-                                logger.warn("Could not copy from " + baseJspFile.getAbsolutePath() + " to " + jspFile.getAbsolutePath(),
-                                        ex);
+                                logger.warn("Could not copy from {} to {}", baseJspFile.getAbsolutePath(), jspFile.getAbsolutePath(), ex);
                             }
                         }
                     });
diff --git a/src/main/java/org/codelibs/fess/helper/ThemeHelper.java b/src/main/java/org/codelibs/fess/helper/ThemeHelper.java
index 0ce00723b..25c7e6c48 100644
--- a/src/main/java/org/codelibs/fess/helper/ThemeHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/ThemeHelper.java
@@ -117,12 +117,12 @@ public class ThemeHelper {
                 try {
                     Files.delete(f);
                 } catch (final IOException e) {
-                    logger.warn("Failed to delete " + f, e);
+                    logger.warn("Failed to delete {}", f, e);
                 }
             });
             Files.deleteIfExists(dir);
         } catch (final IOException e) {
-            logger.warn("Failed to delete " + dir, e);
+            logger.warn("Failed to delete {}", dir, e);
         }
     }
 
diff --git a/src/main/java/org/codelibs/fess/helper/ViewHelper.java b/src/main/java/org/codelibs/fess/helper/ViewHelper.java
index 7ac3985cd..01045b7c9 100644
--- a/src/main/java/org/codelibs/fess/helper/ViewHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/ViewHelper.java
@@ -361,7 +361,7 @@ public class ViewHelper {
                     url = URLDecoder.decode(url.replace("+", "%2B"), urlLinkEncoding);
                 } catch (final Exception e) {
                     if (logger.isDebugEnabled()) {
-                        logger.warn("Failed to decode " + url, e);
+                        logger.warn("Failed to decode {}", url, e);
                     }
                 }
             }
@@ -712,7 +712,7 @@ public class ViewHelper {
             final String encodedName = URLEncoder.encode(name, Constants.UTF_8).replace("+", "%20");
             response.header(CONTENT_DISPOSITION, contentDispositionType + "; filename=\"" + name + "\"; filename*=utf-8''" + encodedName);
         } catch (final Exception e) {
-            logger.warn("Failed to write a filename: " + responseData, e);
+            logger.warn("Failed to write a filename: {}", responseData, e);
         }
     }
 
diff --git a/src/main/java/org/codelibs/fess/helper/WebFsIndexHelper.java b/src/main/java/org/codelibs/fess/helper/WebFsIndexHelper.java
index 54c3fe524..63b662ad6 100644
--- a/src/main/java/org/codelibs/fess/helper/WebFsIndexHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/WebFsIndexHelper.java
@@ -450,7 +450,7 @@ public class WebFsIndexHelper {
             // clear url filter
             urlFilterService.delete(sid);
         } catch (final Exception e) {
-            logger.warn("Failed to delete UrlFilter for " + sid, e);
+            logger.warn("Failed to delete UrlFilter for {}", sid, e);
         }
 
         try {
@@ -458,14 +458,14 @@ public class WebFsIndexHelper {
             urlQueueService.clearCache();
             urlQueueService.delete(sid);
         } catch (final Exception e) {
-            logger.warn("Failed to delete UrlQueue for " + sid, e);
+            logger.warn("Failed to delete UrlQueue for {}", sid, e);
         }
 
         try {
             // clear
             dataService.delete(sid);
         } catch (final Exception e) {
-            logger.warn("Failed to delete AccessResult for " + sid, e);
+            logger.warn("Failed to delete AccessResult for {}", sid, e);
         }
     }
 
diff --git a/src/main/java/org/codelibs/fess/indexer/IndexUpdater.java b/src/main/java/org/codelibs/fess/indexer/IndexUpdater.java
index a49d15d0c..047c4e05b 100644
--- a/src/main/java/org/codelibs/fess/indexer/IndexUpdater.java
+++ b/src/main/java/org/codelibs/fess/indexer/IndexUpdater.java
@@ -142,17 +142,17 @@ public class IndexUpdater extends Thread {
         try {
             urlFilterService.delete(sessionId);
         } catch (final Exception e) {
-            logger.warn("Failed to delete url filters: " + sessionId, e);
+            logger.warn("Failed to delete url filters: {}", sessionId, e);
         }
         try {
             urlQueueService.delete(sessionId);
         } catch (final Exception e) {
-            logger.warn("Failed to delete url queues: " + sessionId, e);
+            logger.warn("Failed to delete url queues: {}", sessionId, e);
         }
         try {
             dataService.delete(sessionId);
         } catch (final Exception e) {
-            logger.warn("Failed to delete data: " + sessionId, e);
+            logger.warn("Failed to delete data: {}", sessionId, e);
         }
     }
 
@@ -258,7 +258,7 @@ public class IndexUpdater extends Thread {
                         throw e;
                     }
                     errorCount++;
-                    logger.warn("Failed to access data. Retry to access.. " + errorCount, e);
+                    logger.warn("Failed to access data. Retry to access it {} times.", errorCount, e);
                 } finally {
                     if (systemHelper.isForceStop()) {
                         finishCrawling = true;
@@ -386,7 +386,7 @@ public class IndexUpdater extends Thread {
                         logger.debug("The number of an added document is {}.", documentSize);
                     }
                 } catch (final Exception e) {
-                    logger.warn("Could not add a doc: " + accessResult.getUrl(), e);
+                    logger.warn("Could not add a doc: {}", accessResult.getUrl(), e);
                 }
             } else {
                 if (logger.isDebugEnabled()) {
diff --git a/src/main/java/org/codelibs/fess/job/PurgeDocJob.java b/src/main/java/org/codelibs/fess/job/PurgeDocJob.java
index a87d001c5..751cbe0ea 100644
--- a/src/main/java/org/codelibs/fess/job/PurgeDocJob.java
+++ b/src/main/java/org/codelibs/fess/job/PurgeDocJob.java
@@ -39,7 +39,7 @@ public class PurgeDocJob {
             fessEsClient.deleteByQuery(fessConfig.getIndexDocumentUpdateIndex(), queryBuilder);
 
         } catch (final Exception e) {
-            logger.error("Could not delete expired documents: " + queryBuilder.toString(), e);
+            logger.error("Could not delete expired documents: {}", queryBuilder.toString(), e);
             resultBuf.append(e.getMessage()).append("\n");
         }
 
diff --git a/src/main/java/org/codelibs/fess/job/UpdateLabelJob.java b/src/main/java/org/codelibs/fess/job/UpdateLabelJob.java
index 0df562b0c..6c2d5bafa 100644
--- a/src/main/java/org/codelibs/fess/job/UpdateLabelJob.java
+++ b/src/main/java/org/codelibs/fess/job/UpdateLabelJob.java
@@ -62,7 +62,7 @@ public class UpdateLabelJob {
                         return builder.setScript(script);
                     }
                 } catch (final Exception e) {
-                    logger.warn("Failed to process " + hit, e);
+                    logger.warn("Failed to process {}", hit, e);
                 }
                 return null;
             });
diff --git a/src/main/java/org/codelibs/fess/thumbnail/ThumbnailManager.java b/src/main/java/org/codelibs/fess/thumbnail/ThumbnailManager.java
index a0bf9619f..1143e46ac 100644
--- a/src/main/java/org/codelibs/fess/thumbnail/ThumbnailManager.java
+++ b/src/main/java/org/codelibs/fess/thumbnail/ThumbnailManager.java
@@ -265,7 +265,7 @@ public class ThumbnailManager {
                 logger.debug("No image file exists: {}", noImageFile.getAbsolutePath());
             }
         } catch (final Exception e) {
-            logger.warn("Failed to create thumbnail for " + entity, e);
+            logger.warn("Failed to create thumbnail for {}", entity, e);
         }
     }
 
@@ -416,7 +416,7 @@ public class ThumbnailManager {
                     parent = parent.getParent();
                 }
             } catch (final IOException e) {
-                logger.warn("Failed to delete " + path, e);
+                logger.warn("Failed to delete {}", path, e);
             }
         }
 
@@ -456,7 +456,7 @@ public class ThumbnailManager {
         @Override
         public FileVisitResult visitFileFailed(final Path file, final IOException e) throws IOException {
             if (e != null) {
-                logger.warn("I/O exception on " + file, e);
+                logger.warn("I/O exception on {}", file, e);
             }
             return FileVisitResult.CONTINUE;
         }
@@ -464,7 +464,7 @@ public class ThumbnailManager {
         @Override
         public FileVisitResult postVisitDirectory(final Path dir, final IOException e) throws IOException {
             if (e != null) {
-                logger.warn("I/O exception on " + dir, e);
+                logger.warn("I/O exception on {}", dir, e);
             }
             deleteEmptyDirectory(dir);
             return FileVisitResult.CONTINUE;
@@ -507,7 +507,7 @@ public class ThumbnailManager {
                             Files.move(path, newPath);
                             logger.info("Move {} to {}", path, newPath);
                         } catch (final IOException e) {
-                            logger.warn("Failed to move " + path, e);
+                            logger.warn("Failed to move {}", path, e);
                         }
                     }
                 });
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 0f8efaf8b..2e9b9a284 100644
--- a/src/main/java/org/codelibs/fess/thumbnail/impl/BaseThumbnailGenerator.java
+++ b/src/main/java/org/codelibs/fess/thumbnail/impl/BaseThumbnailGenerator.java
@@ -154,7 +154,7 @@ public abstract class BaseThumbnailGenerator implements ThumbnailGenerator {
             ComponentUtil.getIndexingHelper().updateDocument(ComponentUtil.getFessEsClient(), thumbnailId,
                     fessConfig.getIndexFieldThumbnail(), value);
         } catch (final Exception e) {
-            logger.warn("Failed to update thumbnail field at " + thumbnailId, e);
+            logger.warn("Failed to update thumbnail field at {}", thumbnailId, e);
         }
     }
 
@@ -181,10 +181,10 @@ public abstract class BaseThumbnailGenerator implements ThumbnailGenerator {
             if (e.getCause() == null) {
                 logger.debug(e.getMessage());
             } else {
-                logger.warn("Failed to process " + id, e);
+                logger.warn("Failed to process {}", id, e);
             }
         } catch (final Exception e) {
-            logger.warn("Failed to process " + id, e);
+            logger.warn("Failed to process {}", id, e);
         }
         return false;
     }
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 54ccbac99..0bd188258 100644
--- a/src/main/java/org/codelibs/fess/thumbnail/impl/CommandGenerator.java
+++ b/src/main/java/org/codelibs/fess/thumbnail/impl/CommandGenerator.java
@@ -164,7 +164,7 @@ public class CommandGenerator extends BaseThumbnailGenerator {
                 p.destroy();
             }
         } catch (final Exception e) {
-            logger.warn("Failed to generate a thumbnail of " + thumbnailId, e);
+            logger.warn("Failed to generate a thumbnail of {}", thumbnailId, e);
         }
         if (task != null) {
             task.cancel();
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 eb206a148..fcc5cbeeb 100644
--- a/src/main/java/org/codelibs/fess/thumbnail/impl/HtmlTagBasedGenerator.java
+++ b/src/main/java/org/codelibs/fess/thumbnail/impl/HtmlTagBasedGenerator.java
@@ -109,10 +109,10 @@ public class HtmlTagBasedGenerator extends BaseThumbnailGenerator {
                 }
             } catch (final Throwable t) {
                 if (logger.isDebugEnabled()) {
-                    logger.warn("Failed to create thumbnail: " + thumbnailId + " -> " + responseData.getUrl(), t);
+                    logger.warn("Failed to create thumbnail: {} -> {}", thumbnailId, responseData.getUrl(), t);
                 } else {
-                    logger.warn("Failed to create thumbnail: " + thumbnailId + " -> " + responseData.getUrl() + " ("
-                            + t.getClass().getCanonicalName() + ": " + t.getMessage() + ")");
+                    logger.warn("Failed to create thumbnail: {} -> {} ({}:{})", thumbnailId, responseData.getUrl(),
+                            t.getClass().getCanonicalName(), t.getMessage());
                 }
             } finally {
                 if (!created) {
diff --git a/src/main/java/org/codelibs/fess/util/GroovyUtil.java b/src/main/java/org/codelibs/fess/util/GroovyUtil.java
index 0af6a34cb..6fb89b3d0 100644
--- a/src/main/java/org/codelibs/fess/util/GroovyUtil.java
+++ b/src/main/java/org/codelibs/fess/util/GroovyUtil.java
@@ -43,7 +43,7 @@ public final class GroovyUtil {
         } catch (final JobProcessingException e) {
             throw e;
         } catch (final Exception e) {
-            logger.warn("Failed to evalue groovy script: " + template + " => " + paramMap, e);
+            logger.warn("Failed to evalue groovy script: {} => {}", template, paramMap, e);
             return null;
         } finally {
             final GroovyClassLoader loader = groovyShell.getClassLoader();
diff --git a/src/main/java/org/codelibs/fess/util/ThreadDumpUtil.java b/src/main/java/org/codelibs/fess/util/ThreadDumpUtil.java
index d15bbf555..db933d2fb 100644
--- a/src/main/java/org/codelibs/fess/util/ThreadDumpUtil.java
+++ b/src/main/java/org/codelibs/fess/util/ThreadDumpUtil.java
@@ -58,7 +58,7 @@ public class ThreadDumpUtil {
                 }
             });
         } catch (final Exception e) {
-            logger.warn("Failed to write a thread dump to " + file, e);
+            logger.warn("Failed to write a thread dump to {}", file, e);
         }
     }
 
diff --git a/src/main/java/org/codelibs/fess/util/UpgradeUtil.java b/src/main/java/org/codelibs/fess/util/UpgradeUtil.java
index 3ad523fb0..2e1bc0bd2 100644
--- a/src/main/java/org/codelibs/fess/util/UpgradeUtil.java
+++ b/src/main/java/org/codelibs/fess/util/UpgradeUtil.java
@@ -58,7 +58,7 @@ public final class UpgradeUtil {
                 }
             }
         } catch (final Exception e) {
-            logger.warn("Failed to register " + filePath, e);
+            logger.warn("Failed to register {}", filePath, e);
         }
         return false;
     }
@@ -83,7 +83,7 @@ public final class UpgradeUtil {
         } catch (final ResourceNotFoundRuntimeException e) {
             // ignore
         } catch (final Exception e) {
-            logger.warn(aliasConfigPath + " is not found.", e);
+            logger.warn("{} is not found.", aliasConfigPath, e);
         }
         return false;
     }
@@ -100,7 +100,7 @@ public final class UpgradeUtil {
             try {
                 source = FileUtil.readUTF8(mappingFile);
             } catch (final Exception e) {
-                logger.warn(mappingFile + " is not found.", e);
+                logger.warn("{} is not found.", mappingFile, e);
             }
             try {
                 final AcknowledgedResponse putMappingResponse = indicesClient.preparePutMapping(index).setSource(source, XContentType.JSON)
@@ -113,7 +113,7 @@ public final class UpgradeUtil {
                 }
                 // TODO bulk
             } catch (final Exception e) {
-                logger.warn("Failed to create " + index + "/" + type + " mapping.", e);
+                logger.warn("Failed to create {}/{} mapping.", index, type, e);
             }
         }
         return false;
@@ -134,7 +134,7 @@ public final class UpgradeUtil {
                     return true;
                 }
             } catch (final Exception e) {
-                logger.warn("Failed to add " + field + " to " + index + "/" + type, e);
+                logger.warn("Failed to add {} to {}/{} ", field, index, type, e);
             }
         }
         return false;
@@ -154,7 +154,7 @@ public final class UpgradeUtil {
                 return true;
             }
         } catch (final Exception e) {
-            logger.warn("Failed to update " + index + " settings.", e);
+            logger.warn("Failed to update {} settings.", index, e);
         }
 
         return false;
@@ -166,7 +166,7 @@ public final class UpgradeUtil {
             fessEsClient.index(indexRequest).actionGet();
             return true;
         } catch (final Exception e) {
-            logger.warn("Failed to add " + id + " to " + index, e);
+            logger.warn("Failed to add {} to {}", id, index, e);
         }
         return false;
     }
@@ -196,7 +196,7 @@ public final class UpgradeUtil {
 
             @Override
             public void onFailure(final Exception e) {
-                logger.warn("Failed to delete " + index + " index.", e);
+                logger.warn("Failed to delete {} index.", index, e);
             }
         });
     }