diff --git a/oap-server/server-cluster-plugin/cluster-standalone-plugin/src/main/java/org/apache/skywalking/oap/server/cluster/plugin/standalone/StandaloneManager.java b/oap-server/server-cluster-plugin/cluster-standalone-plugin/src/main/java/org/apache/skywalking/oap/server/cluster/plugin/standalone/StandaloneManager.java
index c266eb4e5..3535e2b34 100644
--- a/oap-server/server-cluster-plugin/cluster-standalone-plugin/src/main/java/org/apache/skywalking/oap/server/cluster/plugin/standalone/StandaloneManager.java
+++ b/oap-server/server-cluster-plugin/cluster-standalone-plugin/src/main/java/org/apache/skywalking/oap/server/cluster/plugin/standalone/StandaloneManager.java
@@ -18,16 +18,14 @@
 
 package org.apache.skywalking.oap.server.cluster.plugin.standalone;
 
+import java.util.ArrayList;
+import java.util.List;
 import org.apache.skywalking.oap.server.core.cluster.ClusterNodesQuery;
 import org.apache.skywalking.oap.server.core.cluster.ClusterRegister;
 import org.apache.skywalking.oap.server.core.cluster.RemoteInstance;
 
-import java.util.ArrayList;
-import java.util.List;
-
 /**
- * A cluster manager simulator. Work in memory only.
- * Also return the current instance.
+ * A cluster manager simulator. Work in memory only. Also return the current instance.
  *
  * @author peng-yongsheng, Wu Sheng
  */
@@ -35,14 +33,13 @@ public class StandaloneManager implements ClusterNodesQuery, ClusterRegister {
 
     private volatile RemoteInstance remoteInstance;
 
-
     @Override public void registerRemote(RemoteInstance remoteInstance) {
         this.remoteInstance = remoteInstance;
     }
 
     @Override
     public List<RemoteInstance> queryRemoteNodes() {
-        if(remoteInstance == null){
+        if (remoteInstance == null) {
             return new ArrayList(0);
         }
         ArrayList remoteList = new ArrayList(1);
diff --git a/oap-server/server-cluster-plugin/cluster-standalone-plugin/src/test/java/org/apache/skywalking/oap/server/cluster/plugin/standalone/StandaloneManagerTest.java b/oap-server/server-cluster-plugin/cluster-standalone-plugin/src/test/java/org/apache/skywalking/oap/server/cluster/plugin/standalone/StandaloneManagerTest.java
index 267949290..2e6913030 100644
--- a/oap-server/server-cluster-plugin/cluster-standalone-plugin/src/test/java/org/apache/skywalking/oap/server/cluster/plugin/standalone/StandaloneManagerTest.java
+++ b/oap-server/server-cluster-plugin/cluster-standalone-plugin/src/test/java/org/apache/skywalking/oap/server/cluster/plugin/standalone/StandaloneManagerTest.java
@@ -24,7 +24,7 @@ import org.junit.Test;
 
 public class StandaloneManagerTest {
     @Test
-    public void test(){
+    public void test() {
         StandaloneManager standaloneManager = new StandaloneManager();
         RemoteInstance remote1 = new RemoteInstance();
         RemoteInstance remote2 = new RemoteInstance();
diff --git a/oap-server/server-cluster-plugin/cluster-zookeeper-plugin/src/test/java/org/apache/skywalking/oap/server/cluster/plugin/zookeeper/ClusterModuleZookeeperProviderTestCase.java b/oap-server/server-cluster-plugin/cluster-zookeeper-plugin/src/test/java/org/apache/skywalking/oap/server/cluster/plugin/zookeeper/ClusterModuleZookeeperProviderTestCase.java
index fafd1275e..bbffa9ffc 100644
--- a/oap-server/server-cluster-plugin/cluster-zookeeper-plugin/src/test/java/org/apache/skywalking/oap/server/cluster/plugin/zookeeper/ClusterModuleZookeeperProviderTestCase.java
+++ b/oap-server/server-cluster-plugin/cluster-zookeeper-plugin/src/test/java/org/apache/skywalking/oap/server/cluster/plugin/zookeeper/ClusterModuleZookeeperProviderTestCase.java
@@ -67,7 +67,7 @@ public class ClusterModuleZookeeperProviderTestCase {
 
         for (int i = 0; i < 20; i++) {
             List<RemoteInstance> detailsList = clusterNodesQuery.queryRemoteNodes();
-            if(detailsList.size() == 0){
+            if (detailsList.size() == 0) {
                 Thread.sleep(500);
                 continue;
             }
diff --git a/oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/CoreModuleProvider.java b/oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/CoreModuleProvider.java
index f58f2073e..1af3873de 100644
--- a/oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/CoreModuleProvider.java
+++ b/oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/CoreModuleProvider.java
@@ -82,7 +82,7 @@ public class CoreModuleProvider extends ModuleProvider {
 
     }
 
-    @Override public void notifyAfterCompleted() throws ModuleStartException{
+    @Override public void notifyAfterCompleted() throws ModuleStartException {
         try {
             grpcServer.start();
             jettyServer.start();