diff --git a/client/src/main/java/com/alibaba/nacos/client/config/http/ServerHttpAgent.java b/client/src/main/java/com/alibaba/nacos/client/config/http/ServerHttpAgent.java
index f26135c1248..fb419366f9b 100644
--- a/client/src/main/java/com/alibaba/nacos/client/config/http/ServerHttpAgent.java
+++ b/client/src/main/java/com/alibaba/nacos/client/config/http/ServerHttpAgent.java
@@ -65,8 +65,7 @@ public class ServerHttpAgent implements HttpAgent {
     public HttpResult httpGet(String path, List<String> headers, List<String> paramValues, String encoding,
                               long readTimeoutMs) throws IOException {
         final long endTime = System.currentTimeMillis() + readTimeoutMs;
-
-        boolean isSSL = false;
+        final boolean isSSL = false;
 
         do {
             try {
diff --git a/client/src/main/java/com/alibaba/nacos/client/config/impl/ClientWorker.java b/client/src/main/java/com/alibaba/nacos/client/config/impl/ClientWorker.java
index cb881d677d3..374cbc616d5 100644
--- a/client/src/main/java/com/alibaba/nacos/client/config/impl/ClientWorker.java
+++ b/client/src/main/java/com/alibaba/nacos/client/config/impl/ClientWorker.java
@@ -505,8 +505,6 @@ public void run() {
         }
     }
 
-    // =================
-
     public boolean isHealthServer() {
         return isHealthServer;
     }
@@ -515,16 +513,16 @@ private void setHealthServer(boolean isHealthServer) {
         this.isHealthServer = isHealthServer;
     }
 
-    final ScheduledExecutorService executor;
-    final ExecutorService executorService;
+    private final ScheduledExecutorService executor;
+    private final ExecutorService executorService;
     /**
      * groupKey -> cacheData
      */
-    AtomicReference<Map<String, CacheData>> cacheMap = new AtomicReference<Map<String, CacheData>>(
+    private final AtomicReference<Map<String, CacheData>> cacheMap = new AtomicReference<Map<String, CacheData>>(
         new HashMap<String, CacheData>());
 
-    HttpAgent agent;
-    ConfigFilterChainManager configFilterChainManager;
+    private final HttpAgent agent;
+    private final ConfigFilterChainManager configFilterChainManager;
     private boolean isHealthServer = true;
     private double currentLongingTaskCount = 0;
 }
diff --git a/client/src/main/java/com/alibaba/nacos/client/naming/NacosNamingService.java b/client/src/main/java/com/alibaba/nacos/client/naming/NacosNamingService.java
index 8e5e0d2d332..d92492d3af9 100644
--- a/client/src/main/java/com/alibaba/nacos/client/naming/NacosNamingService.java
+++ b/client/src/main/java/com/alibaba/nacos/client/naming/NacosNamingService.java
@@ -45,6 +45,8 @@
  */
 @SuppressWarnings("PMD.ServiceOrDaoClassShouldEndWithImplRule")
 public class NacosNamingService implements NamingService {
+    private static final String DEFAULT_PORT = "8080";
+
     /**
      * Each Naming instance should have different namespace.
      */
@@ -74,7 +76,6 @@ public NacosNamingService(String serverList) {
     }
 
     public NacosNamingService(Properties properties) {
-
         init(properties);
     }
 
@@ -147,7 +148,7 @@ private void initCacheDir() {
             cacheDir = System.getProperty("user.home") + "/nacos/naming/" + namespace;
         }
     }
-
+  
     @Override
     public void registerInstance(String serviceName, String ip, int port) throws NacosException {
         registerInstance(serviceName, ip, port, Constants.DEFAULT_CLUSTER_NAME);
diff --git a/client/src/main/java/com/alibaba/nacos/client/naming/cache/ConcurrentDiskUtil.java b/client/src/main/java/com/alibaba/nacos/client/naming/cache/ConcurrentDiskUtil.java
index ce21c440366..74ed569f9ba 100644
--- a/client/src/main/java/com/alibaba/nacos/client/naming/cache/ConcurrentDiskUtil.java
+++ b/client/src/main/java/com/alibaba/nacos/client/naming/cache/ConcurrentDiskUtil.java
@@ -211,6 +211,6 @@ private static void sleep(int time) {
         }
     }
 
-    static final int RETRY_COUNT = 10;
-    static final int SLEEP_BASETIME = 10;
+    private static final int RETRY_COUNT = 10;
+    private static final int SLEEP_BASETIME = 10;
 }
diff --git a/client/src/main/java/com/alibaba/nacos/client/naming/core/HostReactor.java b/client/src/main/java/com/alibaba/nacos/client/naming/core/HostReactor.java
index 444093de228..e43dd67634a 100644
--- a/client/src/main/java/com/alibaba/nacos/client/naming/core/HostReactor.java
+++ b/client/src/main/java/com/alibaba/nacos/client/naming/core/HostReactor.java
@@ -36,9 +36,9 @@
  */
 public class HostReactor {
 
-    public static final long DEFAULT_DELAY = 1000L;
+    private static final long DEFAULT_DELAY = 1000L;
 
-    public long updateHoldInterval = 5000L;
+    private static final long UPDATE_HOLD_INTERVAL = 5000L;
 
     private final Map<String, ScheduledFuture<?>> futureMap = new HashMap<String, ScheduledFuture<?>>();
 
@@ -234,11 +234,11 @@ public ServiceInfo getServiceInfo(final String serviceName, final String cluster
 
         } else if (updatingMap.containsKey(serviceName)) {
 
-            if (updateHoldInterval > 0) {
+            if (UPDATE_HOLD_INTERVAL > 0) {
                 // hold a moment waiting for update finish
                 synchronized (serviceObj) {
                     try {
-                        serviceObj.wait(updateHoldInterval);
+                        serviceObj.wait(UPDATE_HOLD_INTERVAL);
                     } catch (InterruptedException e) {
                         NAMING_LOGGER.error("[getServiceInfo] serviceName:" + serviceName + ", clusters:" + clusters, e);
                     }
diff --git a/client/src/main/java/com/alibaba/nacos/client/utils/EnvUtil.java b/client/src/main/java/com/alibaba/nacos/client/utils/EnvUtil.java
index cf13bf20de2..f3c6671540d 100644
--- a/client/src/main/java/com/alibaba/nacos/client/utils/EnvUtil.java
+++ b/client/src/main/java/com/alibaba/nacos/client/utils/EnvUtil.java
@@ -86,28 +86,22 @@ public static String getSelfLocationTag() {
         return selfLocationTag;
     }
 
-    public static String listToString(List<String> list) {
-        if (list == null) {
+    private static String listToString(List<String> list) {
+        if (list == null || list.isEmpty()) {
             return null;
         }
         StringBuilder result = new StringBuilder();
-        boolean first = true;
-        // 第一个前面不拼接","
         for (String string : list) {
-            if (first) {
-                first = false;
-            } else {
-                result.append(",");
-            }
             result.append(string);
+            result.append(",");
         }
-        return result.toString();
+        return result.toString().substring(0, result.length() - 1);
     }
 
     private static String selfAmorayTag;
     private static String selfVipserverTag;
     private static String selfLocationTag;
-    public final static String AMORY_TAG = "Amory-Tag";
-    public final static String VIPSERVER_TAG = "Vipserver-Tag";
-    public final static String LOCATION_TAG = "Location-Tag";
+    private final static String AMORY_TAG = "Amory-Tag";
+    private final static String VIPSERVER_TAG = "Vipserver-Tag";
+    private final static String LOCATION_TAG = "Location-Tag";
 }
diff --git a/client/src/main/java/com/alibaba/nacos/client/utils/StringUtils.java b/client/src/main/java/com/alibaba/nacos/client/utils/StringUtils.java
index 2fc915ad15a..d510bf5f1d7 100644
--- a/client/src/main/java/com/alibaba/nacos/client/utils/StringUtils.java
+++ b/client/src/main/java/com/alibaba/nacos/client/utils/StringUtils.java
@@ -38,7 +38,7 @@ public static boolean isBlank(String str) {
             return true;
         }
         for (int i = 0; i < strLen; i++) {
-            if ((Character.isWhitespace(str.charAt(i)) == false)) {
+            if (!Character.isWhitespace(str.charAt(i))) {
                 return false;
             }
         }
@@ -46,7 +46,6 @@ public static boolean isBlank(String str) {
     }
 
     public static boolean isNotBlank(String str) {
-
         return !isBlank(str);
     }
 
diff --git a/naming/src/main/java/com/alibaba/nacos/naming/cluster/ServerListManager.java b/naming/src/main/java/com/alibaba/nacos/naming/cluster/ServerListManager.java
index b63ca6a96f5..639ea720374 100644
--- a/naming/src/main/java/com/alibaba/nacos/naming/cluster/ServerListManager.java
+++ b/naming/src/main/java/com/alibaba/nacos/naming/cluster/ServerListManager.java
@@ -41,7 +41,7 @@
 @Component("serverListManager")
 public class ServerListManager {
 
-    public static final int STABLE_PERIOD = 60 * 1000;
+    private static final int STABLE_PERIOD = 60 * 1000;
 
     @Autowired
     private SwitchDomain switchDomain;
diff --git a/naming/src/main/java/com/alibaba/nacos/naming/controllers/InstanceController.java b/naming/src/main/java/com/alibaba/nacos/naming/controllers/InstanceController.java
index 0fc8279c56d..24a85f7f08a 100644
--- a/naming/src/main/java/com/alibaba/nacos/naming/controllers/InstanceController.java
+++ b/naming/src/main/java/com/alibaba/nacos/naming/controllers/InstanceController.java
@@ -235,10 +235,6 @@ public JSONObject beat(HttpServletRequest request) throws Exception {
 
         String clusterName = clientBeat.getCluster();
 
-        if (StringUtils.isBlank(clusterName)) {
-            clusterName = UtilsAndCommons.DEFAULT_CLUSTER_NAME;
-        }
-
         if (Loggers.DEBUG_LOG.isDebugEnabled()) {
             Loggers.DEBUG_LOG.debug("[CLIENT-BEAT] full arguments: beat: {}, serviceName: {}", clientBeat, serviceName);
         }
diff --git a/naming/src/main/java/com/alibaba/nacos/naming/misc/ServerStatusSynchronizer.java b/naming/src/main/java/com/alibaba/nacos/naming/misc/ServerStatusSynchronizer.java
index d7b2c0a46bf..8ec380a45ae 100644
--- a/naming/src/main/java/com/alibaba/nacos/naming/misc/ServerStatusSynchronizer.java
+++ b/naming/src/main/java/com/alibaba/nacos/naming/misc/ServerStatusSynchronizer.java
@@ -18,6 +18,7 @@
 import com.alibaba.nacos.naming.boot.RunningConfig;
 import com.ning.http.client.AsyncCompletionHandler;
 import com.ning.http.client.Response;
+import org.springframework.util.StringUtils;
 
 import java.net.HttpURLConnection;
 import java.util.HashMap;
@@ -31,7 +32,7 @@
 public class ServerStatusSynchronizer implements Synchronizer {
     @Override
     public void send(final String serverIP, Message msg) {
-        if (serverIP == null) {
+        if (StringUtils.isEmpty(serverIP)) {
             return;
         }