make ConfigChangeEvent immutable

dubbo-cluster/src/main/java/org/apache/dubbo/rpc/cluster/router/condition/config/ListenableRouter.java

@@ -24,6 +24,7 @@
 import org.apache.dubbo.configcenter.ConfigChangeEvent;
 import org.apache.dubbo.configcenter.ConfigChangeType;
 import org.apache.dubbo.configcenter.ConfigurationListener;
+import org.apache.dubbo.configcenter.DefaultConfigChangeEvent;
 import org.apache.dubbo.configcenter.DynamicConfiguration;
 import org.apache.dubbo.rpc.Invocation;
 import org.apache.dubbo.rpc.Invoker;
@@ -121,7 +122,7 @@ private synchronized void init(String ruleKey) {
         configuration.addListener(routerKey, this);
         String rule = configuration.getConfig(routerKey);
         if (rule != null) {
-            this.process(new ConfigChangeEvent(routerKey, rule));
+            this.process(new DefaultConfigChangeEvent(routerKey, rule));
         }
     }
 }

dubbo-cluster/src/main/java/org/apache/dubbo/rpc/cluster/router/tag/TagRouter.java

@@ -25,6 +25,7 @@
 import org.apache.dubbo.configcenter.ConfigChangeEvent;
 import org.apache.dubbo.configcenter.ConfigChangeType;
 import org.apache.dubbo.configcenter.ConfigurationListener;
+import org.apache.dubbo.configcenter.DefaultConfigChangeEvent;
 import org.apache.dubbo.configcenter.DynamicConfiguration;
 import org.apache.dubbo.rpc.Invocation;
 import org.apache.dubbo.rpc.Invoker;
@@ -236,7 +237,7 @@ public <T> void notify(List<Invoker<T>> invokers) {
                 application = providerApplication;
                 String rawRule = configuration.getConfig(key);
                 if (rawRule != null) {
-                    this.process(new ConfigChangeEvent(key, rawRule));
+                    this.process(new DefaultConfigChangeEvent(key, rawRule));
                 }
             }
         }

dubbo-configcenter/dubbo-configcenter-api/src/main/java/org/apache/dubbo/configcenter/ConfigChangeEvent.java

@@ -17,47 +17,15 @@
 package org.apache.dubbo.configcenter;
 
 /**
- * Config change event.
+ * This interface only has getters, so it is immutable.
  *
  * @see ConfigChangeType
  */
-public class ConfigChangeEvent {
-    private String key;
+public interface ConfigChangeEvent {
 
-    private String value;
-    private ConfigChangeType changeType;
+    String getKey();
 
-    public ConfigChangeEvent(String key, String value) {
-        this(key, value, ConfigChangeType.MODIFIED);
-    }
+    String getValue();
 
-    public ConfigChangeEvent(String key, String value, ConfigChangeType changeType) {
-        this.key = key;
-        this.value = value;
-        this.changeType = changeType;
-    }
-
-    public String getKey() {
-        return key;
-    }
-
-    public void setKey(String key) {
-        this.key = key;
-    }
-
-    public String getValue() {
-        return value;
-    }
-
-    public void setValue(String value) {
-        this.value = value;
-    }
-
-    public ConfigChangeType getChangeType() {
-        return changeType;
-    }
-
-    public void setChangeType(ConfigChangeType changeType) {
-        this.changeType = changeType;
-    }
+    ConfigChangeType getChangeType(); 
 }

dubbo-configcenter/dubbo-configcenter-api/src/main/java/org/apache/dubbo/configcenter/DefaultConfigChangeEvent.java

@@ -0,0 +1,63 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.dubbo.configcenter;
+
+/**
+ * Default implementation of Config change event.
+ *
+ * @see ConfigChangeType
+ */
+public class DefaultConfigChangeEvent implements ConfigChangeEvent {
+    private String key;
+
+    private String value;
+    private ConfigChangeType changeType;
+
+    public DefaultConfigChangeEvent(String key, String value) {
+        this(key, value, ConfigChangeType.MODIFIED);
+    }
+
+    public DefaultConfigChangeEvent(String key, String value, ConfigChangeType changeType) {
+        this.key = key;
+        this.value = value;
+        this.changeType = changeType;
+    }
+
+    public String getKey() {
+        return key;
+    }
+
+    public void setKey(String key) {
+        this.key = key;
+    }
+
+    public String getValue() {
+        return value;
+    }
+
+    public void setValue(String value) {
+        this.value = value;
+    }
+
+    public ConfigChangeType getChangeType() {
+        return changeType;
+    }
+
+    public void setChangeType(ConfigChangeType changeType) {
+        this.changeType = changeType;
+    }
+}

dubbo-configcenter/dubbo-configcenter-apollo/src/main/java/org/apache/dubbo/configcenter/support/apollo/ApolloDynamicConfiguration.java

@@ -24,6 +24,7 @@
 import org.apache.dubbo.configcenter.ConfigChangeEvent;
 import org.apache.dubbo.configcenter.ConfigChangeType;
 import org.apache.dubbo.configcenter.ConfigurationListener;
+import org.apache.dubbo.configcenter.DefaultConfigChangeEvent;
 import org.apache.dubbo.configcenter.DynamicConfiguration;
 
 import com.ctrip.framework.apollo.Config;
@@ -176,11 +177,8 @@ public void onChange(com.ctrip.framework.apollo.model.ConfigChangeEvent changeEv
                     return;
                 }
 
-                listeners.forEach(listener -> {
-                            ConfigChangeEvent event = new ConfigChangeEvent(key, change.getNewValue(), getChangeType(change));
-                            listener.process(event);
-                        }
-                );
+                ConfigChangeEvent event = new DefaultConfigChangeEvent(key, change.getNewValue(), getChangeType(change));
+                listeners.forEach(listener -> listener.process(event));
             }
         }
 

dubbo-configcenter/dubbo-configcenter-zookeeper/src/main/java/org/apache/dubbo/configcenter/support/zookeeper/CacheListener.java

@@ -21,7 +21,7 @@
 import org.apache.dubbo.configcenter.ConfigChangeEvent;
 import org.apache.dubbo.configcenter.ConfigChangeType;
 import org.apache.dubbo.configcenter.ConfigurationListener;
-
+import org.apache.dubbo.configcenter.DefaultConfigChangeEvent;
 import org.apache.curator.framework.CuratorFramework;
 import org.apache.curator.framework.recipes.cache.ChildData;
 import org.apache.curator.framework.recipes.cache.TreeCacheEvent;
@@ -83,7 +83,7 @@ public void childEvent(CuratorFramework aClient, TreeCacheEvent event) throws Ex
                     return;
             }
 
-            ConfigChangeEvent configChangeEvent = new ConfigChangeEvent(key, new String(value, StandardCharsets.UTF_8), changeType);
+            ConfigChangeEvent configChangeEvent = new DefaultConfigChangeEvent(key, new String(value, StandardCharsets.UTF_8), changeType);
             Set<ConfigurationListener> listeners = keyListeners.get(key);
             if (CollectionUtils.isNotEmpty(listeners)) {
                 listeners.forEach(listener -> listener.process(configChangeEvent));

dubbo-registry/dubbo-registry-api/src/main/java/org/apache/dubbo/registry/integration/AbstractConfiguratorListener.java

@@ -22,6 +22,7 @@
 import org.apache.dubbo.configcenter.ConfigChangeEvent;
 import org.apache.dubbo.configcenter.ConfigChangeType;
 import org.apache.dubbo.configcenter.ConfigurationListener;
+import org.apache.dubbo.configcenter.DefaultConfigChangeEvent;
 import org.apache.dubbo.configcenter.DynamicConfiguration;
 import org.apache.dubbo.rpc.cluster.Configurator;
 import org.apache.dubbo.rpc.cluster.configurator.parser.ConfigParser;
@@ -43,7 +44,7 @@ protected final void initWith(String key) {
         dynamicConfiguration.addListener(key, this);
         String rawConfig = dynamicConfiguration.getConfig(key);
         if (!StringUtils.isEmpty(rawConfig)) {
-            process(new ConfigChangeEvent(key, rawConfig));
+            process(new DefaultConfigChangeEvent(key, rawConfig));
         }
     }