diff --git a/parse/src/main/java/com/alibaba/otter/canal/parse/inbound/mysql/MysqlMultiStageCoprocessor.java b/parse/src/main/java/com/alibaba/otter/canal/parse/inbound/mysql/MysqlMultiStageCoprocessor.java
index 10df2af5..81bbbd08 100644
--- a/parse/src/main/java/com/alibaba/otter/canal/parse/inbound/mysql/MysqlMultiStageCoprocessor.java
+++ b/parse/src/main/java/com/alibaba/otter/canal/parse/inbound/mysql/MysqlMultiStageCoprocessor.java
@@ -387,7 +387,7 @@ public class MysqlMultiStageCoprocessor extends AbstractCanalLifeCycle implement
         }
     }
 
-    class MessageEvent {
+    static class MessageEvent {
 
         private LogBuffer        buffer;
         private CanalEntry.Entry entry;
@@ -437,7 +437,7 @@ public class MysqlMultiStageCoprocessor extends AbstractCanalLifeCycle implement
 
     }
 
-    class SimpleFatalExceptionHandler implements ExceptionHandler {
+    static class SimpleFatalExceptionHandler implements ExceptionHandler {
 
         @Override
         public void handleEventException(final Throwable ex, final long sequence, final Object event) {
diff --git a/prometheus/src/main/java/com/alibaba/otter/canal/prometheus/impl/EntryCollector.java b/prometheus/src/main/java/com/alibaba/otter/canal/prometheus/impl/EntryCollector.java
index 29ecc977..5c7802df 100644
--- a/prometheus/src/main/java/com/alibaba/otter/canal/prometheus/impl/EntryCollector.java
+++ b/prometheus/src/main/java/com/alibaba/otter/canal/prometheus/impl/EntryCollector.java
@@ -125,7 +125,7 @@ public class EntryCollector extends Collector implements InstanceRegistry {
         }
     }
 
-    private class EntryMetricsHolder {
+    private static class EntryMetricsHolder {
         private AtomicLong   latestExecTime;
         private AtomicLong   transactionCounter;
         private List<String> destLabelValues;
diff --git a/prometheus/src/main/java/com/alibaba/otter/canal/prometheus/impl/MetaCollector.java b/prometheus/src/main/java/com/alibaba/otter/canal/prometheus/impl/MetaCollector.java
index 1259663a..3500e0da 100644
--- a/prometheus/src/main/java/com/alibaba/otter/canal/prometheus/impl/MetaCollector.java
+++ b/prometheus/src/main/java/com/alibaba/otter/canal/prometheus/impl/MetaCollector.java
@@ -81,7 +81,7 @@ public class MetaCollector extends Collector implements InstanceRegistry {
         instances.remove(destination);
     }
 
-    private class MetaMetricsHolder {
+    private static class MetaMetricsHolder {
         private List<String>     infoLabelValues;
         private List<String>     destLabelValues;
         private CanalMetaManager metaManager;
diff --git a/prometheus/src/main/java/com/alibaba/otter/canal/prometheus/impl/ParserCollector.java b/prometheus/src/main/java/com/alibaba/otter/canal/prometheus/impl/ParserCollector.java
index 660bf1ca..ad2b2051 100644
--- a/prometheus/src/main/java/com/alibaba/otter/canal/prometheus/impl/ParserCollector.java
+++ b/prometheus/src/main/java/com/alibaba/otter/canal/prometheus/impl/ParserCollector.java
@@ -141,7 +141,7 @@ public class ParserCollector extends Collector implements InstanceRegistry {
         instances.remove(destination);
     }
 
-    private class ParserMetricsHolder {
+    private static class ParserMetricsHolder {
         private List<String> parserLabelValues;
         private List<String> modeLabelValues;
         // metrics for single parser
@@ -151,7 +151,7 @@ public class ParserCollector extends Collector implements InstanceRegistry {
         private boolean      isParallel;
     }
 
-    private class GroupParserMetricsHolder extends ParserMetricsHolder {
+    private static class GroupParserMetricsHolder extends ParserMetricsHolder {
         private final List<ParserMetricsHolder> holders = new ArrayList<>();
     }
 
diff --git a/prometheus/src/main/java/com/alibaba/otter/canal/prometheus/impl/SinkCollector.java b/prometheus/src/main/java/com/alibaba/otter/canal/prometheus/impl/SinkCollector.java
index 0918c84a..a6921130 100644
--- a/prometheus/src/main/java/com/alibaba/otter/canal/prometheus/impl/SinkCollector.java
+++ b/prometheus/src/main/java/com/alibaba/otter/canal/prometheus/impl/SinkCollector.java
@@ -80,7 +80,7 @@ public class SinkCollector extends Collector implements InstanceRegistry {
         instances.remove(destination);
     }
 
-    private class SinkMetricsHolder {
+    private static class SinkMetricsHolder {
 
         private AtomicLong   eventsSinkBlockingTime;
         private List<String> destLabelValues;
diff --git a/prometheus/src/main/java/com/alibaba/otter/canal/prometheus/impl/StoreCollector.java b/prometheus/src/main/java/com/alibaba/otter/canal/prometheus/impl/StoreCollector.java
index 6305c51e..e22eb251 100644
--- a/prometheus/src/main/java/com/alibaba/otter/canal/prometheus/impl/StoreCollector.java
+++ b/prometheus/src/main/java/com/alibaba/otter/canal/prometheus/impl/StoreCollector.java
@@ -174,7 +174,7 @@ public class StoreCollector extends Collector implements InstanceRegistry {
         instances.remove(destination);
     }
 
-    private class StoreMetricsHolder {
+    private static class StoreMetricsHolder {
         private AtomicLong   putSeq;
         private AtomicLong   ackSeq;
         private BatchMode    batchMode;