diff --git a/src/main/java/org/codelibs/fess/app/service/CharMappingService.java b/src/main/java/org/codelibs/fess/app/service/CharMappingService.java
index 8dd8414d6..5b833cdf3 100644
--- a/src/main/java/org/codelibs/fess/app/service/CharMappingService.java
+++ b/src/main/java/org/codelibs/fess/app/service/CharMappingService.java
@@ -53,7 +53,7 @@ public class CharMappingService {
     }
 
     public OptionalEntity<CharMappingFile> getCharMappingFile(final String dictId) {
-        return dictionaryManager.getDictionaryFile(dictId).filter(file -> file instanceof CharMappingFile)
+        return dictionaryManager.getDictionaryFile(dictId).filter(CharMappingFile.class::isInstance)
                 .map(file -> OptionalEntity.of((CharMappingFile) file)).orElse(OptionalEntity.empty());
     }
 
diff --git a/src/main/java/org/codelibs/fess/app/service/KuromojiService.java b/src/main/java/org/codelibs/fess/app/service/KuromojiService.java
index 3cda03e12..2456aa39d 100644
--- a/src/main/java/org/codelibs/fess/app/service/KuromojiService.java
+++ b/src/main/java/org/codelibs/fess/app/service/KuromojiService.java
@@ -52,7 +52,7 @@ public class KuromojiService {
     }
 
     public OptionalEntity<KuromojiFile> getKuromojiFile(final String dictId) {
-        return dictionaryManager.getDictionaryFile(dictId).filter(file -> file instanceof KuromojiFile)
+        return dictionaryManager.getDictionaryFile(dictId).filter(KuromojiFile.class::isInstance)
                 .map(file -> OptionalEntity.of((KuromojiFile) file)).orElse(OptionalEntity.empty());
     }
 
diff --git a/src/main/java/org/codelibs/fess/app/service/ProtwordsService.java b/src/main/java/org/codelibs/fess/app/service/ProtwordsService.java
index 6d9e0879b..174d4cec7 100644
--- a/src/main/java/org/codelibs/fess/app/service/ProtwordsService.java
+++ b/src/main/java/org/codelibs/fess/app/service/ProtwordsService.java
@@ -53,7 +53,7 @@ public class ProtwordsService {
     }
 
     public OptionalEntity<ProtwordsFile> getProtwordsFile(final String dictId) {
-        return dictionaryManager.getDictionaryFile(dictId).filter(file -> file instanceof ProtwordsFile)
+        return dictionaryManager.getDictionaryFile(dictId).filter(ProtwordsFile.class::isInstance)
                 .map(file -> OptionalEntity.of((ProtwordsFile) file)).orElse(OptionalEntity.empty());
     }
 
diff --git a/src/main/java/org/codelibs/fess/app/service/StemmerOverrideService.java b/src/main/java/org/codelibs/fess/app/service/StemmerOverrideService.java
index 7939b7fd0..03bc4e30a 100644
--- a/src/main/java/org/codelibs/fess/app/service/StemmerOverrideService.java
+++ b/src/main/java/org/codelibs/fess/app/service/StemmerOverrideService.java
@@ -53,7 +53,7 @@ public class StemmerOverrideService {
     }
 
     public OptionalEntity<StemmerOverrideFile> getStemmerOverrideFile(final String dictId) {
-        return dictionaryManager.getDictionaryFile(dictId).filter(file -> file instanceof StemmerOverrideFile)
+        return dictionaryManager.getDictionaryFile(dictId).filter(StemmerOverrideFile.class::isInstance)
                 .map(file -> OptionalEntity.of((StemmerOverrideFile) file)).orElse(OptionalEntity.empty());
     }
 
diff --git a/src/main/java/org/codelibs/fess/app/service/StopwordsService.java b/src/main/java/org/codelibs/fess/app/service/StopwordsService.java
index 4aca31832..ef8173283 100644
--- a/src/main/java/org/codelibs/fess/app/service/StopwordsService.java
+++ b/src/main/java/org/codelibs/fess/app/service/StopwordsService.java
@@ -53,7 +53,7 @@ public class StopwordsService {
     }
 
     public OptionalEntity<StopwordsFile> getStopwordsFile(final String dictId) {
-        return dictionaryManager.getDictionaryFile(dictId).filter(file -> file instanceof StopwordsFile)
+        return dictionaryManager.getDictionaryFile(dictId).filter(StopwordsFile.class::isInstance)
                 .map(file -> OptionalEntity.of((StopwordsFile) file)).orElse(OptionalEntity.empty());
     }
 
diff --git a/src/main/java/org/codelibs/fess/app/service/SynonymService.java b/src/main/java/org/codelibs/fess/app/service/SynonymService.java
index 63fde54a9..5e9eeb3dd 100644
--- a/src/main/java/org/codelibs/fess/app/service/SynonymService.java
+++ b/src/main/java/org/codelibs/fess/app/service/SynonymService.java
@@ -52,7 +52,7 @@ public class SynonymService {
     }
 
     public OptionalEntity<SynonymFile> getSynonymFile(final String dictId) {
-        return dictionaryManager.getDictionaryFile(dictId).filter(file -> file instanceof SynonymFile)
+        return dictionaryManager.getDictionaryFile(dictId).filter(SynonymFile.class::isInstance)
                 .map(file -> OptionalEntity.of((SynonymFile) file)).orElse(OptionalEntity.empty());
     }