diff --git a/src/main/java/org/codelibs/fess/api/es/EsApiManager.java b/src/main/java/org/codelibs/fess/api/es/EsApiManager.java
index cb4d1ad2d..03852e920 100644
--- a/src/main/java/org/codelibs/fess/api/es/EsApiManager.java
+++ b/src/main/java/org/codelibs/fess/api/es/EsApiManager.java
@@ -63,7 +63,7 @@ public class EsApiManager extends BaseApiManager {
     @PostConstruct
     public void register() {
         if (logger.isInfoEnabled()) {
-            logger.info("Load " + this.getClass().getSimpleName());
+            logger.info("Load {}", this.getClass().getSimpleName());
         }
         ComponentUtil.getWebApiManagerFactory().add(this);
     }
@@ -179,7 +179,7 @@ public class EsApiManager extends BaseApiManager {
             } catch (final ClientAbortException e) {
                 logger.debug("Client aborts this request.", e);
             } catch (final IOException e) {
-                logger.error("Failed to read " + path + " from " + filePath);
+                logger.error("Failed to read {} from {}", path, filePath);
                 throw new WebApiException(HttpServletResponse.SC_INTERNAL_SERVER_ERROR, e);
             }
         } else {
@@ -189,7 +189,7 @@ public class EsApiManager extends BaseApiManager {
             } catch (final ClientAbortException e) {
                 logger.debug("Client aborts this request.", e);
             } catch (final IOException e) {
-                logger.error("Failed to read " + path + " from " + filePath);
+                logger.error("Failed to read {} from {}", path, filePath);
                 throw new WebApiException(HttpServletResponse.SC_INTERNAL_SERVER_ERROR, e);
             }
         }
diff --git a/src/main/java/org/codelibs/fess/api/gsa/GsaApiManager.java b/src/main/java/org/codelibs/fess/api/gsa/GsaApiManager.java
index 60b05a03c..325adb7dc 100644
--- a/src/main/java/org/codelibs/fess/api/gsa/GsaApiManager.java
+++ b/src/main/java/org/codelibs/fess/api/gsa/GsaApiManager.java
@@ -71,7 +71,7 @@ public class GsaApiManager extends BaseApiManager implements WebApiManager {
     @PostConstruct
     public void register() {
         if (logger.isInfoEnabled()) {
-            logger.info("Load " + this.getClass().getSimpleName());
+            logger.info("Load {}", this.getClass().getSimpleName());
         }
         ComponentUtil.getWebApiManagerFactory().add(this);
     }
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 c48f250cd..b9c821fdd 100644
--- a/src/main/java/org/codelibs/fess/api/json/JsonApiManager.java
+++ b/src/main/java/org/codelibs/fess/api/json/JsonApiManager.java
@@ -72,7 +72,7 @@ public class JsonApiManager extends BaseJsonApiManager {
     @PostConstruct
     public void register() {
         if (logger.isInfoEnabled()) {
-            logger.info("Load " + this.getClass().getSimpleName());
+            logger.info("Load {}", this.getClass().getSimpleName());
         }
         ComponentUtil.getWebApiManagerFactory().add(this);
     }
diff --git a/src/main/java/org/codelibs/fess/api/suggest/SuggestApiManager.java b/src/main/java/org/codelibs/fess/api/suggest/SuggestApiManager.java
index a4fd0d0f9..354f65da1 100644
--- a/src/main/java/org/codelibs/fess/api/suggest/SuggestApiManager.java
+++ b/src/main/java/org/codelibs/fess/api/suggest/SuggestApiManager.java
@@ -59,7 +59,7 @@ public class SuggestApiManager extends BaseJsonApiManager {
     @PostConstruct
     public void register() {
         if (logger.isInfoEnabled()) {
-            logger.info("Load " + this.getClass().getSimpleName());
+            logger.info("Load {}", this.getClass().getSimpleName());
         }
         ComponentUtil.getWebApiManagerFactory().add(this);
     }
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 7bfa3211e..25245ba59 100644
--- a/src/main/java/org/codelibs/fess/app/job/ScriptExecutorJob.java
+++ b/src/main/java/org/codelibs/fess/app/job/ScriptExecutorJob.java
@@ -58,13 +58,13 @@ public class ScriptExecutorJob implements LaJob {
         final String id = scheduledJob.getId();
         final String target = scheduledJob.getTarget();
         if (!ComponentUtil.getFessConfig().isSchedulerTarget(target)) {
-            logger.info("Ignore Job " + id + ":" + scheduledJob.getName() + " because of not target: " + scheduledJob.getTarget());
+            logger.info("Ignore Job {}:{} because of not target: {}", scheduledJob.getName(), id, scheduledJob.getTarget());
             return;
         }
 
         final JobHelper jobHelper = ComponentUtil.getJobHelper();
         if (!jobHelper.isAvailable(id)) {
-            logger.info("Job " + id + " is unavailable. Unregistering this job.");
+            logger.info("Job {} is unavailable. Unregistering this job.", id);
             jobHelper.unregister(scheduledJob);
             return;
         }
@@ -95,17 +95,17 @@ public class ScriptExecutorJob implements LaJob {
             if (logger.isDebugEnabled()) {
                 logger.debug("Starting Job {}. scriptType: {}, script: {}", id, scriptType, script);
             } else if (scheduledJob.isLoggingEnabled() && logger.isInfoEnabled()) {
-                logger.info("Starting Job " + id + ".");
+                logger.info("Starting Job {}.", id);
             }
 
             final Object ret = jobExecutor.execute(script);
             if (ret == null) {
                 if (scheduledJob.isLoggingEnabled() && logger.isInfoEnabled()) {
-                    logger.info("Finished Job " + id + ".");
+                    logger.info("Finished Job {}.", id);
                 }
             } else {
                 if (scheduledJob.isLoggingEnabled() && logger.isInfoEnabled()) {
-                    logger.info("Finished Job " + id + ". The return value is:\n" + ret);
+                    logger.info("Finished Job {}. The return value is:\n{}", id, ret);
                 }
                 jobLog.setScriptResult(ret.toString());
             }
diff --git a/src/main/java/org/codelibs/fess/app/web/admin/design/AdminDesignAction.java b/src/main/java/org/codelibs/fess/app/web/admin/design/AdminDesignAction.java
index 4a21ec0d3..d4490caa0 100644
--- a/src/main/java/org/codelibs/fess/app/web/admin/design/AdminDesignAction.java
+++ b/src/main/java/org/codelibs/fess/app/web/admin/design/AdminDesignAction.java
@@ -166,7 +166,7 @@ public class AdminDesignAction extends FessAdminAction {
 
         final File parentFile = uploadFile.getParentFile();
         if (!parentFile.exists() && !parentFile.mkdirs()) {
-            logger.warn("Could not create " + parentFile.getAbsolutePath());
+            logger.warn("Could not create {}", parentFile.getAbsolutePath());
         }
 
         try {
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 195dc2e22..f4eb5c635 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
@@ -101,7 +101,7 @@ public class AdminEsreqAction extends FessAdminAction {
                     CopyUtil.copy(in, tempFile);
                 } catch (final Exception e1) {
                     if (tempFile != null && tempFile.exists() && !tempFile.delete()) {
-                        logger.warn("Failed to delete " + tempFile.getAbsolutePath());
+                        logger.warn("Failed to delete {}", tempFile.getAbsolutePath());
                     }
                     throw e1;
                 }
@@ -110,7 +110,7 @@ public class AdminEsreqAction extends FessAdminAction {
                         out.write(in);
                     } finally {
                         if (tempFile.exists() && !tempFile.delete()) {
-                            logger.warn("Failed to delete " + tempFile.getAbsolutePath());
+                            logger.warn("Failed to delete {}", tempFile.getAbsolutePath());
                         }
                     }
                 });
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 de9257dc1..88b86558e 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
@@ -124,13 +124,13 @@ public class AdminMaintenanceAction extends FessAdminAction {
                 .execute(
                         ActionListener.wrap(
                                 res -> {
-                                    logger.info("Close " + docIndex);
+                                    logger.info("Close {}", docIndex);
                                     fessEsClient
                                             .admin()
                                             .indices()
                                             .prepareOpen(docIndex)
                                             .execute(
-                                                    ActionListener.wrap(res2 -> logger.info("Open " + docIndex),
+                                                    ActionListener.wrap(res2 -> logger.info("Open {}", docIndex),
                                                             e -> logger.warn("Failed to open " + docIndex, e)));
                                 }, e -> logger.warn("Failed to close " + docIndex, e)));
         saveInfo(messages -> messages.addSuccessStartedDataUpdate(GLOBAL));
@@ -311,7 +311,7 @@ public class AdminMaintenanceAction extends FessAdminAction {
                 fessEsClient.addMapping(docIndex, "doc", toIndex);
                 fessEsClient.reindex(fromIndex, toIndex, replaceAliases);
                 if (replaceAliases && !fessEsClient.updateAlias(toIndex)) {
-                    logger.warn("Failed to update aliases for " + fromIndex + " and " + toIndex);
+                    logger.warn("Failed to update aliases for {} and {}", fromIndex, toIndex);
                 }
             }, e -> logger.warn("Failed to reindex from " + fromIndex + " to " + toIndex, e)));
             return true;
@@ -320,4 +320,4 @@ public class AdminMaintenanceAction extends FessAdminAction {
         return false;
     }
 
-}
\ No newline at end of file
+}
diff --git a/src/main/java/org/codelibs/fess/auth/chain/CommandChain.java b/src/main/java/org/codelibs/fess/auth/chain/CommandChain.java
index 0038f11af..ed52dbcfd 100644
--- a/src/main/java/org/codelibs/fess/auth/chain/CommandChain.java
+++ b/src/main/java/org/codelibs/fess/auth/chain/CommandChain.java
@@ -94,7 +94,7 @@ public class CommandChain implements AuthenticationChain {
         }
 
         if (logger.isInfoEnabled()) {
-            logger.info("Command: " + String.join(" ", commands));
+            logger.info("Command: {}", String.join(" ", commands));
         }
 
         final String[] cmds = stream(commands).get(stream -> stream.map(s -> {
@@ -134,7 +134,7 @@ public class CommandChain implements AuthenticationChain {
             final int exitValue = currentProcess.exitValue();
 
             if (logger.isInfoEnabled()) {
-                logger.info("Exit Code: " + exitValue + " - Process Output:\n" + it.getOutput());
+                logger.info("Exit Code: {} - Process Output:\n{}", exitValue, it.getOutput());
             }
             if (exitValue == 143 && mt.isTeminated()) {
                 throw new CommandExecutionException("The command execution is timeout: " + String.join(" ", commands));
diff --git a/src/main/java/org/codelibs/fess/crawler/transformer/AbstractFessFileTransformer.java b/src/main/java/org/codelibs/fess/crawler/transformer/AbstractFessFileTransformer.java
index 4a21b24d2..43d956acf 100644
--- a/src/main/java/org/codelibs/fess/crawler/transformer/AbstractFessFileTransformer.java
+++ b/src/main/java/org/codelibs/fess/crawler/transformer/AbstractFessFileTransformer.java
@@ -105,7 +105,7 @@ public abstract class AbstractFessFileTransformer extends AbstractTransformer im
                 return null;
             }
             if (getLogger().isDebugEnabled()) {
-                getLogger().debug("ExtractData: " + extractData);
+                getLogger().debug("ExtractData: {}", extractData);
             }
             // meta
             extractData
@@ -154,7 +154,7 @@ public abstract class AbstractFessFileTransformer extends AbstractTransformer im
                                             if (dt != null) {
                                                 dataMap.put(mapping.getValue1(), FessFunctions.formatDate(dt));
                                             } else {
-                                                logger.warn("Failed to parse " + mapping.toString());
+                                                logger.warn("Failed to parse {}", mapping.toString());
                                             }
                                         } else {
                                             logger.warn("Unknown mapping type: {}={}", key, mapping);
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 7fe12d670..ae3610c6e 100644
--- a/src/main/java/org/codelibs/fess/crawler/transformer/FessXpathTransformer.java
+++ b/src/main/java/org/codelibs/fess/crawler/transformer/FessXpathTransformer.java
@@ -235,14 +235,14 @@ public class FessXpathTransformer extends XpathTransformer implements FessTransf
                     }
                 }
                 if (noindex && nofollow) {
-                    logger.info("META(robots=noindex,nofollow): " + responseData.getUrl());
+                    logger.info("META(robots=noindex,nofollow): {}", responseData.getUrl());
                     throw new ChildUrlsException(Collections.emptySet(), "#processMetaRobots");
                 } else if (noindex) {
-                    logger.info("META(robots=noindex): " + responseData.getUrl());
+                    logger.info("META(robots=noindex): {}", responseData.getUrl());
                     storeChildUrls(responseData, resultData);
                     throw new ChildUrlsException(resultData.getChildUrlSet(), "#processMetaRobots");
                 } else if (nofollow) {
-                    logger.info("META(robots=nofollow): " + responseData.getUrl());
+                    logger.info("META(robots=nofollow): {}", responseData.getUrl());
                     responseData.setNoFollow(true);
                 }
             }
@@ -281,14 +281,14 @@ public class FessXpathTransformer extends XpathTransformer implements FessTransf
                         }
                     }
                     if (noindex && nofollow) {
-                        logger.info("HEADER(robots=noindex,nofollow): " + responseData.getUrl());
+                        logger.info("HEADER(robots=noindex,nofollow): {}", responseData.getUrl());
                         throw new ChildUrlsException(Collections.emptySet(), "#processXRobotsTag");
                     } else if (noindex) {
-                        logger.info("HEADER(robots=noindex): " + responseData.getUrl());
+                        logger.info("HEADER(robots=noindex): {}", responseData.getUrl());
                         storeChildUrls(responseData, resultData);
                         throw new ChildUrlsException(resultData.getChildUrlSet(), "#processXRobotsTag");
                     } else if (nofollow) {
-                        logger.info("HEADER(robots=nofollow): " + responseData.getUrl());
+                        logger.info("HEADER(robots=nofollow): {}", responseData.getUrl());
                         responseData.setNoFollow(true);
                     }
                 });
@@ -345,7 +345,7 @@ public class FessXpathTransformer extends XpathTransformer implements FessTransf
                 && isValidCanonicalUrl(responseData.getUrl(), canonicalUrl)) {
             final Set<RequestData> childUrlSet = new HashSet<>();
             childUrlSet.add(RequestDataBuilder.newRequestData().get().url(canonicalUrl).build());
-            logger.info("CANONICAL: " + responseData.getUrl() + " -> " + canonicalUrl);
+            logger.info("CANONICAL: {} -> {}", responseData.getUrl(), canonicalUrl);
             throw new ChildUrlsException(childUrlSet, this.getClass().getName() + "#putAdditionalData");
         }
 
@@ -593,7 +593,7 @@ public class FessXpathTransformer extends XpathTransformer implements FessTransf
                 parseTextContent(node, buf);
             }
         } catch (final Exception e) {
-            logger.warn("Could not parse a value of " + xpath);
+            logger.warn("Could not parse a value of {}", xpath);
         }
         if (buf == null) {
             return null;
@@ -781,7 +781,7 @@ public class FessXpathTransformer extends XpathTransformer implements FessTransf
         }
 
         if (u == null) {
-            logger.warn("Ignored child URL: " + attrValue + " in " + url);
+            logger.warn("Ignored child URL: {} in {}", attrValue, url);
             return;
         }
 
diff --git a/src/main/java/org/codelibs/fess/dict/kuromoji/KuromojiCreator.java b/src/main/java/org/codelibs/fess/dict/kuromoji/KuromojiCreator.java
index f306a5178..f10f7ea5c 100644
--- a/src/main/java/org/codelibs/fess/dict/kuromoji/KuromojiCreator.java
+++ b/src/main/java/org/codelibs/fess/dict/kuromoji/KuromojiCreator.java
@@ -35,7 +35,7 @@ public class KuromojiCreator extends DictionaryCreator {
     @PostConstruct
     public void register() {
         if (logger.isInfoEnabled()) {
-            logger.info("Load " + this.getClass().getSimpleName());
+            logger.info("Load {}", this.getClass().getSimpleName());
         }
         dictionaryManager.addCreator(this);
     }
diff --git a/src/main/java/org/codelibs/fess/dict/mapping/CharMappingCreator.java b/src/main/java/org/codelibs/fess/dict/mapping/CharMappingCreator.java
index ecb5e3f76..49407804a 100644
--- a/src/main/java/org/codelibs/fess/dict/mapping/CharMappingCreator.java
+++ b/src/main/java/org/codelibs/fess/dict/mapping/CharMappingCreator.java
@@ -35,7 +35,7 @@ public class CharMappingCreator extends DictionaryCreator {
     @PostConstruct
     public void register() {
         if (logger.isInfoEnabled()) {
-            logger.info("Load " + this.getClass().getSimpleName());
+            logger.info("Load {}", this.getClass().getSimpleName());
         }
         dictionaryManager.addCreator(this);
     }
diff --git a/src/main/java/org/codelibs/fess/dict/mapping/CharMappingFile.java b/src/main/java/org/codelibs/fess/dict/mapping/CharMappingFile.java
index 6e7923ea8..d4358992c 100644
--- a/src/main/java/org/codelibs/fess/dict/mapping/CharMappingFile.java
+++ b/src/main/java/org/codelibs/fess/dict/mapping/CharMappingFile.java
@@ -152,7 +152,7 @@ public class CharMappingFile extends DictionaryFile<CharMappingItem> {
                 final Matcher m = parsePattern.matcher(replacedLine);
 
                 if (!m.find()) {
-                    logger.warn("Failed to parse " + line + " in " + path);
+                    logger.warn("Failed to parse {} in {}", line, path);
                     if (updater != null) {
                         updater.write("# " + line);
                     }
@@ -163,7 +163,7 @@ public class CharMappingFile extends DictionaryFile<CharMappingItem> {
                 output = m.group(2).trim();
 
                 if (inputs == null || output == null || inputs.length == 0) {
-                    logger.warn("Failed to parse " + line + " in " + path);
+                    logger.warn("Failed to parse {} in {}", line, path);
                     if (updater != null) {
                         updater.write("# " + line);
                     }
diff --git a/src/main/java/org/codelibs/fess/dict/protwords/ProtwordsCreator.java b/src/main/java/org/codelibs/fess/dict/protwords/ProtwordsCreator.java
index 9f5d2ad60..bf7861b3d 100644
--- a/src/main/java/org/codelibs/fess/dict/protwords/ProtwordsCreator.java
+++ b/src/main/java/org/codelibs/fess/dict/protwords/ProtwordsCreator.java
@@ -35,7 +35,7 @@ public class ProtwordsCreator extends DictionaryCreator {
     @PostConstruct
     public void register() {
         if (logger.isInfoEnabled()) {
-            logger.info("Load " + this.getClass().getSimpleName());
+            logger.info("Load {}", this.getClass().getSimpleName());
         }
         dictionaryManager.addCreator(this);
     }
diff --git a/src/main/java/org/codelibs/fess/dict/stemmeroverride/StemmerOverrideCreator.java b/src/main/java/org/codelibs/fess/dict/stemmeroverride/StemmerOverrideCreator.java
index 1521ae196..f1f51eace 100644
--- a/src/main/java/org/codelibs/fess/dict/stemmeroverride/StemmerOverrideCreator.java
+++ b/src/main/java/org/codelibs/fess/dict/stemmeroverride/StemmerOverrideCreator.java
@@ -35,7 +35,7 @@ public class StemmerOverrideCreator extends DictionaryCreator {
     @PostConstruct
     public void register() {
         if (logger.isInfoEnabled()) {
-            logger.info("Load " + this.getClass().getSimpleName());
+            logger.info("Load {}", this.getClass().getSimpleName());
         }
         dictionaryManager.addCreator(this);
     }
diff --git a/src/main/java/org/codelibs/fess/dict/stemmeroverride/StemmerOverrideFile.java b/src/main/java/org/codelibs/fess/dict/stemmeroverride/StemmerOverrideFile.java
index 7dff6f158..eedf1ec33 100644
--- a/src/main/java/org/codelibs/fess/dict/stemmeroverride/StemmerOverrideFile.java
+++ b/src/main/java/org/codelibs/fess/dict/stemmeroverride/StemmerOverrideFile.java
@@ -149,7 +149,7 @@ public class StemmerOverrideFile extends DictionaryFile<StemmerOverrideItem> {
                 final Matcher m = parsePattern.matcher(replacedLine);
 
                 if (!m.find()) {
-                    logger.warn("Failed to parse " + line + " in " + path);
+                    logger.warn("Failed to parse {} in {}", line, path);
                     if (updater != null) {
                         updater.write("# " + line);
                     }
@@ -160,7 +160,7 @@ public class StemmerOverrideFile extends DictionaryFile<StemmerOverrideItem> {
                 final String output = m.group(2).trim();
 
                 if (input == null || output == null) {
-                    logger.warn("Failed to parse " + line + " in " + path);
+                    logger.warn("Failed to parse {} to {}", line, path);
                     if (updater != null) {
                         updater.write("# " + line);
                     }
diff --git a/src/main/java/org/codelibs/fess/dict/stopwords/StopwordsCreator.java b/src/main/java/org/codelibs/fess/dict/stopwords/StopwordsCreator.java
index 905edc84b..c0e4d2bcb 100644
--- a/src/main/java/org/codelibs/fess/dict/stopwords/StopwordsCreator.java
+++ b/src/main/java/org/codelibs/fess/dict/stopwords/StopwordsCreator.java
@@ -35,7 +35,7 @@ public class StopwordsCreator extends DictionaryCreator {
     @PostConstruct
     public void register() {
         if (logger.isInfoEnabled()) {
-            logger.info("Load " + this.getClass().getSimpleName());
+            logger.info("Load {}", this.getClass().getSimpleName());
         }
         dictionaryManager.addCreator(this);
     }
diff --git a/src/main/java/org/codelibs/fess/dict/synonym/SynonymCreator.java b/src/main/java/org/codelibs/fess/dict/synonym/SynonymCreator.java
index 11e6577eb..5a61befc0 100644
--- a/src/main/java/org/codelibs/fess/dict/synonym/SynonymCreator.java
+++ b/src/main/java/org/codelibs/fess/dict/synonym/SynonymCreator.java
@@ -35,7 +35,7 @@ public class SynonymCreator extends DictionaryCreator {
     @PostConstruct
     public void register() {
         if (logger.isInfoEnabled()) {
-            logger.info("Load " + this.getClass().getSimpleName());
+            logger.info("Load {}", this.getClass().getSimpleName());
         }
         dictionaryManager.addCreator(this);
     }
diff --git a/src/main/java/org/codelibs/fess/ds/AbstractDataStore.java b/src/main/java/org/codelibs/fess/ds/AbstractDataStore.java
index 02fd9f617..231d03c3e 100644
--- a/src/main/java/org/codelibs/fess/ds/AbstractDataStore.java
+++ b/src/main/java/org/codelibs/fess/ds/AbstractDataStore.java
@@ -131,7 +131,7 @@ public abstract class AbstractDataStore implements DataStore {
             try {
                 readInterval = Long.parseLong(value);
             } catch (final NumberFormatException e) {
-                logger.warn("Invalid read interval: " + value);
+                logger.warn("Invalid read interval: {}", value);
             }
         }
         return readInterval;
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 b3af1aa74..1ca984a24 100644
--- a/src/main/java/org/codelibs/fess/ds/callback/FileListIndexUpdateCallbackImpl.java
+++ b/src/main/java/org/codelibs/fess/ds/callback/FileListIndexUpdateCallbackImpl.java
@@ -94,7 +94,7 @@ public class FileListIndexUpdateCallbackImpl implements IndexUpdateCallback {
                 // deleted file
                 deleteDocument(paramMap, dataMap);
             } else {
-                logger.warn("unknown event: " + eventType + ", data: " + dataMap);
+                logger.warn("unknown event: {}, data: {}", eventType, dataMap);
             }
         });
     }
@@ -108,14 +108,14 @@ public class FileListIndexUpdateCallbackImpl implements IndexUpdateCallback {
         synchronized (indexUpdateCallback) {
             // required check
             if (!dataMap.containsKey(fessConfig.getIndexFieldUrl()) || dataMap.get(fessConfig.getIndexFieldUrl()) == null) {
-                logger.warn("Could not add a doc. Invalid data: " + dataMap);
+                logger.warn("Could not add a doc. Invalid data: {}", dataMap);
                 return;
             }
 
             final String url = dataMap.get(fessConfig.getIndexFieldUrl()).toString();
             final CrawlerClient client = crawlerClientFactory.getClient(url);
             if (client == null) {
-                logger.warn("CrawlerClient is null. Data: " + dataMap);
+                logger.warn("CrawlerClient is null. Data: {}", dataMap);
                 return;
             }
 
@@ -147,7 +147,7 @@ public class FileListIndexUpdateCallbackImpl implements IndexUpdateCallback {
             final RuleManager ruleManager = SingletonLaContainer.getComponent(RuleManager.class);
             final Rule rule = ruleManager.getRule(responseData);
             if (rule == null) {
-                logger.warn("No url rule. Data: " + dataMap);
+                logger.warn("No url rule. Data: {}", dataMap);
             } else {
                 responseData.setRuleId(rule.getRuleId());
                 final ResponseProcessor responseProcessor = rule.getResponseProcessor();
@@ -199,7 +199,7 @@ public class FileListIndexUpdateCallbackImpl implements IndexUpdateCallback {
 
         // required check
         if (!dataMap.containsKey(fessConfig.getIndexFieldUrl()) || dataMap.get(fessConfig.getIndexFieldUrl()) == null) {
-            logger.warn("Could not delete a doc. Invalid data: " + dataMap);
+            logger.warn("Could not delete a doc. Invalid data: {}", dataMap);
             return false;
         }
 
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 b7af70854..c8309773a 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
@@ -224,7 +224,7 @@ public class DataConfig extends BsDataConfig implements CrawlingConfig {
                     final String password = paramMap.get(CRAWLER_FILE_AUTH + "." + fileAuthName + ".password");
 
                     if (StringUtil.isEmpty(username)) {
-                        logger.warn("username is empty. fileAuth:" + fileAuthName);
+                        logger.warn("username is empty. fileAuth:{}", fileAuthName);
                         continue;
                     }
 
@@ -263,7 +263,7 @@ public class DataConfig extends BsDataConfig implements CrawlingConfig {
                     final String password = paramMap.get(CRAWLER_FILE_AUTH + "." + fileAuthName + ".password");
 
                     if (StringUtil.isEmpty(username)) {
-                        logger.warn("username is empty. fileAuth:" + fileAuthName);
+                        logger.warn("username is empty. fileAuth:{}", fileAuthName);
                         continue;
                     }
 
diff --git a/src/main/java/org/codelibs/fess/exec/Crawler.java b/src/main/java/org/codelibs/fess/exec/Crawler.java
index 710eac7dc..a05e304fe 100644
--- a/src/main/java/org/codelibs/fess/exec/Crawler.java
+++ b/src/main/java/org/codelibs/fess/exec/Crawler.java
@@ -244,7 +244,7 @@ public class Crawler {
                             if (Constants.CRAWLER_PROCESS_COMMAND_THREAD_DUMP.equals(command)) {
                                 ThreadDumpUtil.printThreadDump();
                             } else {
-                                logger.warn("Unknown process command: " + command);
+                                logger.warn("Unknown process command: {}", command);
                             }
                             if (Thread.interrupted()) {
                                 return;
@@ -364,7 +364,7 @@ public class Crawler {
                 }
                 buf.append(entry.getKey()).append('=').append(entry.getValue());
             }
-            logger.info("[CRAWL INFO] " + buf.toString());
+            logger.info("[CRAWL INFO] {}", buf.toString());
 
             // notification
             try {
@@ -530,7 +530,7 @@ public class Crawler {
             try {
                 crawlerThread.join();
             } catch (final Exception e) {
-                logger.info("Interrupted a crawling process: " + crawlerThread.getName());
+                logger.info("Interrupted a crawling process: {}", crawlerThread.getName());
             }
         }
     }
diff --git a/src/main/java/org/codelibs/fess/exec/ThumbnailGenerator.java b/src/main/java/org/codelibs/fess/exec/ThumbnailGenerator.java
index 6ff266972..66c89348e 100644
--- a/src/main/java/org/codelibs/fess/exec/ThumbnailGenerator.java
+++ b/src/main/java/org/codelibs/fess/exec/ThumbnailGenerator.java
@@ -141,7 +141,7 @@ public class ThumbnailGenerator {
 
             final int totalCount = process(options);
             if (totalCount != 0) {
-                logger.info("Created " + totalCount + " thumbnail files.");
+                logger.info("Created {} thumbnail files.", totalCount);
             } else {
                 logger.info("No new thumbnails found.");
             }
diff --git a/src/main/java/org/codelibs/fess/helper/CrawlingInfoHelper.java b/src/main/java/org/codelibs/fess/helper/CrawlingInfoHelper.java
index 0b2980bbe..a8d74cdc9 100644
--- a/src/main/java/org/codelibs/fess/helper/CrawlingInfoHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/CrawlingInfoHelper.java
@@ -107,7 +107,7 @@ public class CrawlingInfoHelper {
     public void updateParams(final String sessionId, final String name, final int dayForCleanup) {
         final CrawlingInfo crawlingInfo = getCrawlingInfoService().getLast(sessionId);
         if (crawlingInfo == null) {
-            logger.warn("No crawling session: " + sessionId);
+            logger.warn("No crawling session: {}", sessionId);
             return;
         }
         if (StringUtil.isNotBlank(name)) {
diff --git a/src/main/java/org/codelibs/fess/helper/DataIndexHelper.java b/src/main/java/org/codelibs/fess/helper/DataIndexHelper.java
index 2bbeea301..a2edf0dd9 100644
--- a/src/main/java/org/codelibs/fess/helper/DataIndexHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/DataIndexHelper.java
@@ -161,7 +161,7 @@ public class DataIndexHelper {
         final long execTime = System.currentTimeMillis() - startTime;
         crawlingInfoHelper.putToInfoMap(Constants.DATA_CRAWLING_EXEC_TIME, Long.toString(execTime));
         if (logger.isInfoEnabled()) {
-            logger.info("[EXEC TIME] crawling time: " + execTime + "ms");
+            logger.info("[EXEC TIME] crawling time: {}ms", execTime);
         }
 
         crawlingInfoHelper.putToInfoMap(Constants.DATA_INDEX_EXEC_TIME, Long.toString(indexUpdateCallback.getExecuteTime()));
@@ -210,7 +210,7 @@ public class DataIndexHelper {
             final DataStoreFactory dataStoreFactory = ComponentUtil.getDataStoreFactory();
             dataStore = dataStoreFactory.getDataStore(dataConfig.getHandlerName());
             if (dataStore == null) {
-                logger.error("DataStore(" + dataConfig.getHandlerName() + ") is not found.");
+                logger.error("DataStore({}) is not found.", dataConfig.getHandlerName());
             } else {
                 try {
                     dataStore.store(dataConfig, indexUpdateCallback, initParamMap);
@@ -231,7 +231,7 @@ public class DataIndexHelper {
             }
             final String sessionId = initParamMap.get(Constants.SESSION_ID);
             if (StringUtil.isBlank(sessionId)) {
-                logger.warn("Invalid sessionId at " + dataConfig);
+                logger.warn("Invalid sessionId at {}", dataConfig);
                 return;
             }
             final FessConfig fessConfig = ComponentUtil.getFessConfig();
diff --git a/src/main/java/org/codelibs/fess/helper/IndexingHelper.java b/src/main/java/org/codelibs/fess/helper/IndexingHelper.java
index 7b888f9ef..98d004d0a 100644
--- a/src/main/java/org/codelibs/fess/helper/IndexingHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/IndexingHelper.java
@@ -78,12 +78,12 @@ public class IndexingHelper {
             }
             if (logger.isInfoEnabled()) {
                 if (docList.getContentSize() > 0) {
-                    logger.info("Sent " + docList.size() + " docs (Doc:{process " + docList.getProcessingTime() + "ms, send "
-                            + (System.currentTimeMillis() - execTime) + "ms, size "
-                            + MemoryUtil.byteCountToDisplaySize(docList.getContentSize()) + "}, " + MemoryUtil.getMemoryUsageLog() + ")");
+                    logger.info("Sent {} docs (Doc:{process {}ms, send {}ms, size {}}, {})", docList.size(), docList.getProcessingTime(),
+                            (System.currentTimeMillis() - execTime), MemoryUtil.byteCountToDisplaySize(docList.getContentSize()),
+                            MemoryUtil.getMemoryUsageLog());
                 } else {
-                    logger.info("Sent " + docList.size() + " docs (Doc:{send " + (System.currentTimeMillis() - execTime) + "ms}, "
-                            + MemoryUtil.getMemoryUsageLog() + ")");
+                    logger.info("Sent {}  docs (Doc:{send {}ms}, {})", docList.size(), (System.currentTimeMillis() - execTime),
+                            MemoryUtil.getMemoryUsageLog());
                 }
             }
         } finally {
diff --git a/src/main/java/org/codelibs/fess/helper/JobHelper.java b/src/main/java/org/codelibs/fess/helper/JobHelper.java
index 65023aa26..8f8702063 100644
--- a/src/main/java/org/codelibs/fess/helper/JobHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/JobHelper.java
@@ -59,7 +59,7 @@ public class JobHelper {
 
         final String id = scheduledJob.getId();
         if (!Constants.T.equals(scheduledJob.getAvailable())) {
-            logger.info("Inactive Job " + id + ":" + scheduledJob.getName());
+            logger.info("Inactive Job {}:{}", id, scheduledJob.getName());
             try {
                 unregister(scheduledJob);
             } catch (final Exception e) {
@@ -76,35 +76,35 @@ public class JobHelper {
                     final Map<String, Object> params = new HashMap<>();
                     ComponentUtil.getComponent(ScheduledJobBhv.class).selectByPK(scheduledJob.getId())
                             .ifPresent(e -> params.put(Constants.SCHEDULED_JOB, e)).orElse(() -> {
-                                logger.warn("Job " + scheduledJob.getId() + " is not found.");
+                                logger.warn("Job {} is not found.", scheduledJob.getId());
                             });
                     return params;
                 };
         findJobByUniqueOf(LaJobUnique.of(id)).ifPresent(job -> {
             if (!job.isUnscheduled()) {
                 if (StringUtil.isNotBlank(scheduledJob.getCronExpression())) {
-                    logger.info("Starting Job " + id + ":" + scheduledJob.getName());
+                    logger.info("Starting Job {}:{}", id, scheduledJob.getName());
                     final String cronExpression = scheduledJob.getCronExpression();
                     job.reschedule(cronExpression, op -> op.changeNoticeLogToDebug().params(paramsOp));
                 } else {
-                    logger.info("Inactive Job " + id + ":" + scheduledJob.getName());
+                    logger.info("Inactive Job {}:{}", id, scheduledJob.getName());
                     job.becomeNonCron();
                 }
             } else if (StringUtil.isNotBlank(scheduledJob.getCronExpression())) {
-                logger.info("Starting Job " + id + ":" + scheduledJob.getName());
+                logger.info("Starting Job {}:{}", id, scheduledJob.getName());
                 final String cronExpression = scheduledJob.getCronExpression();
                 job.reschedule(cronExpression, op -> op.changeNoticeLogToDebug().params(paramsOp));
             }
         }).orElse(
                 () -> {
                     if (StringUtil.isNotBlank(scheduledJob.getCronExpression())) {
-                        logger.info("Starting Job " + id + ":" + scheduledJob.getName());
+                        logger.info("Starting Job {}:{}", id, scheduledJob.getName());
                         final String cronExpression = scheduledJob.getCronExpression();
                         cron.register(cronExpression, fessConfig.getSchedulerJobClassAsClass(),
                                 fessConfig.getSchedulerConcurrentExecModeAsEnum(),
                                 op -> op.uniqueBy(id).changeNoticeLogToDebug().params(paramsOp));
                     } else {
-                        logger.info("Inactive Job " + id + ":" + scheduledJob.getName());
+                        logger.info("Inactive Job {}:{}", id, scheduledJob.getName());
                         cron.registerNonCron(fessConfig.getSchedulerJobClassAsClass(), fessConfig.getSchedulerConcurrentExecModeAsEnum(),
                                 op -> op.uniqueBy(id).changeNoticeLogToDebug().params(paramsOp));
                     }
diff --git a/src/main/java/org/codelibs/fess/helper/OpenSearchHelper.java b/src/main/java/org/codelibs/fess/helper/OpenSearchHelper.java
index ae579ba0f..d1e3fb729 100644
--- a/src/main/java/org/codelibs/fess/helper/OpenSearchHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/OpenSearchHelper.java
@@ -56,7 +56,7 @@ public class OpenSearchHelper {
             osddFile = new File(path);
             if (!osddFile.isFile()) {
                 osddFile = null;
-                logger.warn(path + " was not found.");
+                logger.warn("{} was not found.", path);
             }
         } else {
             logger.info("OSDD file is not found.");
diff --git a/src/main/java/org/codelibs/fess/helper/ProcessHelper.java b/src/main/java/org/codelibs/fess/helper/ProcessHelper.java
index 252f2974b..ce090a0c7 100644
--- a/src/main/java/org/codelibs/fess/helper/ProcessHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/ProcessHelper.java
@@ -47,11 +47,11 @@ public class ProcessHelper {
     public void destroy() {
         for (final String sessionId : runningProcessMap.keySet()) {
             if (logger.isInfoEnabled()) {
-                logger.info("Stopping process " + sessionId);
+                logger.info("Stopping process {}", sessionId);
             }
             if (destroyProcess(sessionId) == 0) {
                 if (logger.isInfoEnabled()) {
-                    logger.info("Stopped process " + sessionId);
+                    logger.info("Stopped process {}", sessionId);
                 }
             }
         }
diff --git a/src/main/java/org/codelibs/fess/helper/RelatedContentHelper.java b/src/main/java/org/codelibs/fess/helper/RelatedContentHelper.java
index 9001365a0..d1332d1cb 100644
--- a/src/main/java/org/codelibs/fess/helper/RelatedContentHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/RelatedContentHelper.java
@@ -77,7 +77,7 @@ public class RelatedContentHelper {
             if (entity.getTerm().startsWith(regexPrefix)) {
                 final String regex = entity.getTerm().substring(regexPrefix.length());
                 if (StringUtil.isBlank(regex)) {
-                    logger.warn("Unknown regex pattern: " + entity.getTerm());
+                    logger.warn("Unknown regex pattern: {}", entity.getTerm());
                 } else {
                     pair.getSecond().add(new Pair<>(Pattern.compile(regex), entity.getContent()));
                 }
diff --git a/src/main/java/org/codelibs/fess/helper/SearchLogHelper.java b/src/main/java/org/codelibs/fess/helper/SearchLogHelper.java
index 162cd4ad1..e20782baf 100644
--- a/src/main/java/org/codelibs/fess/helper/SearchLogHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/SearchLogHelper.java
@@ -328,7 +328,7 @@ public class SearchLogHelper {
                     }
                     clickCountMap.put(docId, countObj);
                 }).orElse(() -> {
-                    logger.warn("Not Found for SearchLog: " + clickLog);
+                    logger.warn("Not Found for SearchLog: {}", clickLog);
                 });
             } catch (final Exception e) {
                 logger.warn("Failed to process: " + clickLog, e);
diff --git a/src/main/java/org/codelibs/fess/helper/WebFsIndexHelper.java b/src/main/java/org/codelibs/fess/helper/WebFsIndexHelper.java
index b2647a176..54c3fe524 100644
--- a/src/main/java/org/codelibs/fess/helper/WebFsIndexHelper.java
+++ b/src/main/java/org/codelibs/fess/helper/WebFsIndexHelper.java
@@ -144,7 +144,7 @@ public class WebFsIndexHelper {
                 try {
                     urlFilterService.delete(sid);
                 } catch (final Exception e) {
-                    logger.warn("Failed to delete url filters for " + sid);
+                    logger.warn("Failed to delete url filters for {}", sid);
                 }
             }
 
@@ -156,7 +156,7 @@ public class WebFsIndexHelper {
                     final String u = duplicateHostHelper.convert(urlValue);
                     crawler.addUrl(u);
                     if (logger.isInfoEnabled()) {
-                        logger.info("Target URL: " + u);
+                        logger.info("Target URL: {}", u);
                     }
                 }
             }));
@@ -166,7 +166,7 @@ public class WebFsIndexHelper {
                 if (!urlValue.startsWith("#")) {
                     crawler.addIncludeFilter(urlValue);
                     if (logger.isInfoEnabled()) {
-                        logger.info("Included URL: " + urlValue);
+                        logger.info("Included URL: {}", urlValue);
                     }
                 }
             }));
@@ -176,7 +176,7 @@ public class WebFsIndexHelper {
                 if (!urlValue.startsWith("#")) {
                     crawler.addExcludeFilter(urlValue);
                     if (logger.isInfoEnabled()) {
-                        logger.info("Excluded URL: " + urlValue);
+                        logger.info("Excluded URL: {}", urlValue);
                     }
                 }
             }));
@@ -188,7 +188,7 @@ public class WebFsIndexHelper {
                     final String urlValue = Pattern.quote(u);
                     crawler.addExcludeFilter(urlValue);
                     if (logger.isInfoEnabled()) {
-                        logger.info("Excluded URL from failures: " + urlValue);
+                        logger.info("Excluded URL from failures: {}", urlValue);
                     }
                 });
             }
@@ -250,7 +250,7 @@ public class WebFsIndexHelper {
                 try {
                     urlFilterService.delete(sid);
                 } catch (final Exception e) {
-                    logger.warn("Failed to delete url filters for " + sid);
+                    logger.warn("Failed to delete url filters for {}", sid);
                 }
             }
 
@@ -269,7 +269,7 @@ public class WebFsIndexHelper {
                     }
                     crawler.addUrl(u);
                     if (logger.isInfoEnabled()) {
-                        logger.info("Target Path: " + u);
+                        logger.info("Target Path: {}", u);
                     }
                 }
             }));
@@ -287,7 +287,7 @@ public class WebFsIndexHelper {
                     }
                     crawler.addIncludeFilter(urlValue);
                     if (logger.isInfoEnabled()) {
-                        logger.info("Included Path: " + urlValue);
+                        logger.info("Included Path: {}", urlValue);
                     }
                 } else if (line.startsWith("#DISABLE_URL_ENCODE")) {
                     urlEncodeDisabled.set(true);
@@ -307,7 +307,7 @@ public class WebFsIndexHelper {
                     }
                     crawler.addExcludeFilter(urlValue);
                     if (logger.isInfoEnabled()) {
-                        logger.info("Excluded Path: " + urlValue);
+                        logger.info("Excluded Path: {}", urlValue);
                     }
                 } else if (line.startsWith("#DISABLE_URL_ENCODE")) {
                     urlEncodeDisabled.set(true);
@@ -321,7 +321,7 @@ public class WebFsIndexHelper {
                     final String urlValue = Pattern.quote(u);
                     crawler.addExcludeFilter(urlValue);
                     if (logger.isInfoEnabled()) {
-                        logger.info("Excluded Path from failures: " + urlValue);
+                        logger.info("Excluded Path from failures: {}", urlValue);
                     }
                 });
             }
@@ -409,7 +409,7 @@ public class WebFsIndexHelper {
         final long execTime = System.currentTimeMillis() - startTime;
         crawlingInfoHelper.putToInfoMap(Constants.WEB_FS_CRAWLING_EXEC_TIME, Long.toString(execTime));
         if (logger.isInfoEnabled()) {
-            logger.info("[EXEC TIME] crawling time: " + execTime + "ms");
+            logger.info("[EXEC TIME] crawling time: {}ms", execTime);
         }
 
         indexUpdater.setFinishCrawling(true);
diff --git a/src/main/java/org/codelibs/fess/indexer/IndexUpdater.java b/src/main/java/org/codelibs/fess/indexer/IndexUpdater.java
index 8261215c9..45964fdfd 100644
--- a/src/main/java/org/codelibs/fess/indexer/IndexUpdater.java
+++ b/src/main/java/org/codelibs/fess/indexer/IndexUpdater.java
@@ -259,7 +259,7 @@ public class IndexUpdater extends Thread {
 
                 if (emptyListCount >= maxEmptyListCount) {
                     if (logger.isInfoEnabled()) {
-                        logger.info("Terminating indexUpdater. " + "emptyListCount is over " + maxEmptyListCount + ".");
+                        logger.info("Terminating indexUpdater. emptyListCount is over {}.", maxEmptyListCount);
                     }
                     // terminate crawling
                     finishCrawling = true;
@@ -303,7 +303,7 @@ public class IndexUpdater extends Thread {
         }
 
         if (logger.isInfoEnabled()) {
-            logger.info("[EXEC TIME] index update time: " + executeTime + "ms");
+            logger.info("[EXEC TIME] index update time: {}ms", executeTime);
         }
 
     }
@@ -334,14 +334,14 @@ public class IndexUpdater extends Thread {
                     final Transformer transformer = ComponentUtil.getComponent(accessResultData.getTransformerName());
                     if (transformer == null) {
                         // no transformer
-                        logger.warn("No transformer: " + accessResultData.getTransformerName());
+                        logger.warn("No transformer: {}", accessResultData.getTransformerName());
                         continue;
                     }
                     @SuppressWarnings("unchecked")
                     final Map<String, Object> map = (Map<String, Object>) transformer.getData(accessResultData);
                     if (map.isEmpty()) {
                         // no transformer
-                        logger.warn("No data: " + accessResult.getUrl());
+                        logger.warn("No data: {}", accessResult.getUrl());
                         continue;
                     }
 
@@ -501,8 +501,7 @@ public class IndexUpdater extends Thread {
         final IntervalControlHelper intervalControlHelper = ComponentUtil.getIntervalControlHelper();
         if (totalHits > unprocessedDocumentSize && intervalControlHelper.isCrawlerRunning()) {
             if (logger.isInfoEnabled()) {
-                logger.info("Stopped all crawler threads. " + " You have " + totalHits + " (>" + unprocessedDocumentSize + ") "
-                        + " unprocessed docs.");
+                logger.info("Stopped all crawler threads. You have {} (>{}) unprocessed docs.", totalHits, unprocessedDocumentSize);
             }
             intervalControlHelper.setCrawlerRunning(false);
         }
@@ -525,7 +524,7 @@ public class IndexUpdater extends Thread {
         finishedSessionIdList.clear();
 
         if (logger.isInfoEnabled()) {
-            logger.info("Deleted completed document data. " + "The execution time is " + (System.currentTimeMillis() - execTime) + "ms.");
+            logger.info("Deleted completed document data. The execution time is {}ms.", (System.currentTimeMillis() - execTime));
         }
     }
 
diff --git a/src/main/java/org/codelibs/fess/score/ScoreBooster.java b/src/main/java/org/codelibs/fess/score/ScoreBooster.java
index 0a7eb56c0..66f15f550 100644
--- a/src/main/java/org/codelibs/fess/score/ScoreBooster.java
+++ b/src/main/java/org/codelibs/fess/score/ScoreBooster.java
@@ -104,7 +104,7 @@ public abstract class ScoreBooster {
         if (bulkRequestBuilder != null) {
             final BulkResponse response = bulkRequestBuilder.execute().actionGet(requestTimeout);
             if (response.hasFailures()) {
-                logger.warn("Failed to update scores: " + response.buildFailureMessage());
+                logger.warn("Failed to update scores: {}", response.buildFailureMessage());
             }
             bulkRequestBuilder = null;
         }
diff --git a/src/main/java/org/codelibs/fess/sso/SsoManager.java b/src/main/java/org/codelibs/fess/sso/SsoManager.java
index 0fc8c87aa..9d793c495 100644
--- a/src/main/java/org/codelibs/fess/sso/SsoManager.java
+++ b/src/main/java/org/codelibs/fess/sso/SsoManager.java
@@ -58,7 +58,7 @@ public class SsoManager {
 
     public void register(final SsoAuthenticator authenticator) {
         if (logger.isInfoEnabled()) {
-            logger.info("Load " + authenticator.getClass().getSimpleName());
+            logger.info("Load {}", authenticator.getClass().getSimpleName());
         }
         authenticatorList.add(authenticator);
     }
diff --git a/src/main/java/org/codelibs/fess/thumbnail/ThumbnailManager.java b/src/main/java/org/codelibs/fess/thumbnail/ThumbnailManager.java
index ef683290b..eaf4a8fa6 100644
--- a/src/main/java/org/codelibs/fess/thumbnail/ThumbnailManager.java
+++ b/src/main/java/org/codelibs/fess/thumbnail/ThumbnailManager.java
@@ -104,7 +104,7 @@ public class ThumbnailManager {
             }
         }
         if (baseDir.mkdirs()) {
-            logger.info("Created: " + baseDir.getAbsolutePath());
+            logger.info("Created: {}", baseDir.getAbsolutePath());
         }
         if (!baseDir.isDirectory()) {
             throw new FessSystemException("Not found: " + baseDir.getAbsolutePath());
@@ -246,7 +246,7 @@ public class ThumbnailManager {
             final File noImageFile = new File(outputFile.getAbsolutePath() + NOIMAGE_FILE_SUFFIX);
             if (!noImageFile.isFile() || System.currentTimeMillis() - noImageFile.lastModified() > noImageExpired) {
                 if (noImageFile.isFile() && !noImageFile.delete()) {
-                    logger.warn("Failed to delete " + noImageFile.getAbsolutePath());
+                    logger.warn("Failed to delete {}", noImageFile.getAbsolutePath());
                 }
                 final ThumbnailGenerator generator = ComponentUtil.getComponent(generatorName);
                 if (generator.isAvailable()) {
@@ -259,7 +259,7 @@ public class ThumbnailManager {
                         }
                     }
                 } else {
-                    logger.warn(generatorName + " is not available.");
+                    logger.warn("{} is not available.", generatorName);
                 }
             } else if (logger.isDebugEnabled()) {
                 logger.debug("No image file exists: {}", noImageFile.getAbsolutePath());
@@ -279,7 +279,7 @@ public class ThumbnailManager {
                         logger.debug("Add thumbnail task: {}", task);
                     }
                     if (!thumbnailTaskQueue.offer(task)) {
-                        logger.warn("Failed to add thumbnail task: " + task);
+                        logger.warn("Failed to add thumbnail task: {}", task);
                     }
                     return true;
                 }
@@ -507,7 +507,7 @@ public class ThumbnailManager {
                                 // ignore
                     }
                     Files.move(path, newPath);
-                    logger.info("Move " + path + " to " + newPath);
+                    logger.info("Move {} to {}", path, newPath);
                 } catch (final IOException 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 04a8e047b..adfbe6785 100644
--- a/src/main/java/org/codelibs/fess/thumbnail/impl/BaseThumbnailGenerator.java
+++ b/src/main/java/org/codelibs/fess/thumbnail/impl/BaseThumbnailGenerator.java
@@ -201,7 +201,7 @@ public abstract class BaseThumbnailGenerator implements ThumbnailGenerator {
                     }
 
                     if (logger.isInfoEnabled()) {
-                        logger.info("Generating Thumbnail: " + url);
+                        logger.info("Generating Thumbnail: {}", url);
                     }
 
                     final CrawlerClientFactory crawlerClientFactory =
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 72678d9f5..54ccbac99 100644
--- a/src/main/java/org/codelibs/fess/thumbnail/impl/CommandGenerator.java
+++ b/src/main/java/org/codelibs/fess/thumbnail/impl/CommandGenerator.java
@@ -82,7 +82,7 @@ public class CommandGenerator extends BaseThumbnailGenerator {
             parentFile.mkdirs();
         }
         if (!parentFile.isDirectory()) {
-            logger.warn("Not found: " + parentFile.getAbsolutePath());
+            logger.warn("Not found: {}", parentFile.getAbsolutePath());
             return false;
         }
 
@@ -101,9 +101,9 @@ public class CommandGenerator extends BaseThumbnailGenerator {
                 executeCommand(thumbnailId, cmdList);
 
                 if (outputFile.isFile() && outputFile.length() == 0) {
-                    logger.warn("Thumbnail File is empty. ID is " + thumbnailId);
+                    logger.warn("Thumbnail File is empty. ID is {}", thumbnailId);
                     if (outputFile.delete()) {
-                        logger.info("Deleted: " + outputFile.getAbsolutePath());
+                        logger.info("Deleted: {}", outputFile.getAbsolutePath());
                     }
                     updateThumbnailField(thumbnailId, StringUtil.EMPTY);
                     return false;
@@ -188,7 +188,7 @@ public class CommandGenerator extends BaseThumbnailGenerator {
 
         @Override
         public void run() {
-            logger.warn("CommandGenerator is timed out: " + commandList);
+            logger.warn("CommandGenerator is timed out: {}", commandList);
             try {
                 p.destroyForcibly().waitFor(timeout, TimeUnit.MILLISECONDS);
             } catch (final Exception e) {
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 70f3fe05a..f211709ab 100644
--- a/src/main/java/org/codelibs/fess/thumbnail/impl/HtmlTagBasedGenerator.java
+++ b/src/main/java/org/codelibs/fess/thumbnail/impl/HtmlTagBasedGenerator.java
@@ -74,7 +74,7 @@ public class HtmlTagBasedGenerator extends BaseThumbnailGenerator {
             parentFile.mkdirs();
         }
         if (!parentFile.isDirectory()) {
-            logger.warn("Not found: " + parentFile.getAbsolutePath());
+            logger.warn("Not found: {}", parentFile.getAbsolutePath());
             return false;
         }
 
@@ -95,10 +95,10 @@ public class HtmlTagBasedGenerator extends BaseThumbnailGenerator {
                             created = true;
                             break;
                         case FAILED:
-                            logger.warn("Failed to create thumbnail: " + thumbnailId + " -> " + responseData.getUrl());
+                            logger.warn("Failed to create thumbnail: {} -> {}", thumbnailId, responseData.getUrl());
                             break;
                         case INVALID_SIZE:
-                            logger.info("Unmatched thumbnail size: " + thumbnailId + " -> " + responseData.getUrl());
+                            logger.info("Unmatched thumbnail size: {} -> {}", thumbnailId, responseData.getUrl());
                             break;
                         case NO_IMAGE:
                             if (logger.isDebugEnabled()) {
@@ -106,7 +106,7 @@ public class HtmlTagBasedGenerator extends BaseThumbnailGenerator {
                             }
                             break;
                         default:
-                            logger.error("Unknown thumbnail result: " + thumbnailId + " -> " + responseData.getUrl());
+                            logger.error("Unknown thumbnail result: {} -> {}", thumbnailId, responseData.getUrl());
                             break;
                         }
                     } catch (final Throwable t) {
@@ -120,7 +120,7 @@ public class HtmlTagBasedGenerator extends BaseThumbnailGenerator {
                         if (!created) {
                             updateThumbnailField(thumbnailId, StringUtil.EMPTY);
                             if (outputFile.exists() && !outputFile.delete()) {
-                                logger.warn("Failed to delete " + outputFile.getAbsolutePath());
+                                logger.warn("Failed to delete {}", outputFile.getAbsolutePath());
                             }
                         }
                     }
diff --git a/src/main/java/org/codelibs/fess/util/UpgradeUtil.java b/src/main/java/org/codelibs/fess/util/UpgradeUtil.java
index 7a7376b48..d4ccb0976 100644
--- a/src/main/java/org/codelibs/fess/util/UpgradeUtil.java
+++ b/src/main/java/org/codelibs/fess/util/UpgradeUtil.java
@@ -50,10 +50,10 @@ public final class UpgradeUtil {
             final String source = FileUtil.readUTF8(filePath);
             try (CurlResponse response = ComponentUtil.getCurlHelper().post("/_configsync/file").param("path", path).body(source).execute()) {
                 if (response.getHttpStatusCode() == 200) {
-                    logger.info("Register " + path + " to " + indexName);
+                    logger.info("Register {} to {}", path, indexName);
                     return true;
                 } else {
-                    logger.warn("Invalid request for " + path);
+                    logger.warn("Invalid request for {}", path);
                 }
             }
         } catch (final Exception e) {
@@ -74,7 +74,7 @@ public final class UpgradeUtil {
                         indicesClient.prepareAliases().addAlias(indexName, aliasName, source).execute()
                                 .actionGet(fessConfig.getIndexIndicesTimeout());
                 if (response.isAcknowledged()) {
-                    logger.info("Created " + aliasName + " alias for " + indexName);
+                    logger.info("Created {} alias for {}", aliasName, indexName);
                     return true;
                 } else if (logger.isDebugEnabled()) {
                     logger.debug("Failed to create {} alias for {}", aliasName, indexName);
@@ -107,10 +107,10 @@ public final class UpgradeUtil {
                         indicesClient.preparePutMapping(index).setSource(source, XContentType.JSON).execute()
                                 .actionGet(fessConfig.getIndexIndicesTimeout());
                 if (putMappingResponse.isAcknowledged()) {
-                    logger.info("Created " + index + "/" + type + " mapping.");
+                    logger.info("Created {}/{} mapping.", index, type);
                     return true;
                 } else {
-                    logger.warn("Failed to create " + index + "/" + type + " mapping.");
+                    logger.warn("Failed to create {}/{} mapping.", index, type);
                 }
                 // TODO bulk
             } catch (final Exception e) {
@@ -130,7 +130,7 @@ public final class UpgradeUtil {
                 final AcknowledgedResponse pmResponse =
                         indicesClient.preparePutMapping(index).setSource(source, XContentType.JSON).execute().actionGet();
                 if (!pmResponse.isAcknowledged()) {
-                    logger.warn("Failed to add " + field + " to " + index + "/" + type);
+                    logger.warn("Failed to add {} to {}/{}", field, index, type);
                 } else {
                     return true;
                 }
@@ -150,7 +150,7 @@ public final class UpgradeUtil {
             final PutMappingRequestBuilder builder = indicesClient.preparePutMapping(index).setSource(source, XContentType.JSON);
             final AcknowledgedResponse pmResponse = builder.execute().actionGet();
             if (!pmResponse.isAcknowledged()) {
-                logger.warn("Failed to update " + index + " settings.");
+                logger.warn("Failed to update {} settings.", index);
             } else {
                 return true;
             }
@@ -191,7 +191,7 @@ public final class UpgradeUtil {
 
             @Override
             public void onResponse(final AcknowledgedResponse response) {
-                logger.info("Deleted " + index + " index.");
+                logger.info("Deleted {} index.", index);
                 comsumer.accept(response);
             }
 
diff --git a/src/test/java/org/codelibs/fess/it/CrawlTestBase.java b/src/test/java/org/codelibs/fess/it/CrawlTestBase.java
index 2e5a97aac..9b9b0392d 100644
--- a/src/test/java/org/codelibs/fess/it/CrawlTestBase.java
+++ b/src/test/java/org/codelibs/fess/it/CrawlTestBase.java
@@ -49,7 +49,7 @@ public class CrawlTestBase extends ITBase {
             final String schedulerId = getSchedulerIds(namePrefix).get(0);
             final Response response = checkMethodBase(requestBody).post("/api/admin/scheduler/" + schedulerId + "/start");
             if (response.getBody().jsonPath().getInt("response.status") == 0) {
-                logger.info("Start scheduler \"" + schedulerId + "\"");
+                logger.info("Start scheduler \"{}\"", schedulerId);
                 return;
             }
             try {
diff --git a/src/test/java/org/codelibs/fess/it/CrudTestBase.java b/src/test/java/org/codelibs/fess/it/CrudTestBase.java
index 2f0c221b3..04ff11229 100644
--- a/src/test/java/org/codelibs/fess/it/CrudTestBase.java
+++ b/src/test/java/org/codelibs/fess/it/CrudTestBase.java
@@ -107,7 +107,7 @@ public abstract class CrudTestBase extends ITBase {
             checkPutMethod(requestBody, getItemEndpointSuffix()).then().body("response.created", equalTo(true))
                     .body("response.status", equalTo(0));
 
-            //logger.info("create " + i + checkPutMethod(requestBody, getItemEndpointSuffix()).asString()); // for debugging
+            //logger.info("create {}{}", i, checkPutMethod(requestBody, getItemEndpointSuffix()).asString()); // for debugging
             refresh();
         }
 
diff --git a/src/test/java/org/codelibs/fess/it/ITBase.java b/src/test/java/org/codelibs/fess/it/ITBase.java
index df69f6514..0a1b833d9 100644
--- a/src/test/java/org/codelibs/fess/it/ITBase.java
+++ b/src/test/java/org/codelibs/fess/it/ITBase.java
@@ -40,7 +40,7 @@ public class ITBase {
     public static String settingTestToken() {
         final String testToken = System.getProperty(TEST_TOKEN);
         if (testToken != null) {
-            logger.info("Token: " + testToken);
+            logger.info("Token: {}", testToken);
             return testToken;
         }
 
@@ -50,7 +50,7 @@ public class ITBase {
                         + "\"}}\n{\"updatedTime\":1490250145200,\"updatedBy\":\"admin\",\"createdBy\":\"admin\",\"permissions\":[\"Radmin-api\",\"Rguest\"],\"name\":\"Admin API\",\"createdTime\":1490250145200,\"token\":\""
                         + DEFAULT_TEST_TOKEN + "\"}\n").when().post(getEsUrl() + "/_bulk");
         given().contentType("application/json").when().post(getEsUrl() + "/_refresh");
-        logger.info("Created Token: " + DEFAULT_TEST_TOKEN);
+        logger.info("Created Token: {}", DEFAULT_TEST_TOKEN);
         return DEFAULT_TEST_TOKEN;
     }