[ISSUE#2859]fix no throw exception when publish event but no subscibe…

…r. (alibaba#3364)

client/src/main/java/com/alibaba/nacos/client/config/impl/ServerListManager.java

@@ -19,13 +19,13 @@
 import com.alibaba.nacos.api.PropertyKeyConst;
 import com.alibaba.nacos.api.SystemPropertyKeyConst;
 import com.alibaba.nacos.api.exception.NacosException;
-import com.alibaba.nacos.client.config.impl.EventDispatcher.ServerlistChangeEvent;
 import com.alibaba.nacos.client.config.impl.HttpSimpleClient.HttpResult;
 import com.alibaba.nacos.client.utils.EnvUtil;
 import com.alibaba.nacos.client.utils.LogUtils;
 import com.alibaba.nacos.client.utils.ParamUtil;
 import com.alibaba.nacos.client.utils.TemplateUtils;
 import com.alibaba.nacos.common.lifecycle.Closeable;
+import com.alibaba.nacos.common.notify.NotifyCenter;
 import com.alibaba.nacos.common.utils.IoUtils;
 import com.alibaba.nacos.common.utils.StringUtils;
 import com.alibaba.nacos.common.utils.ThreadUtils;
@@ -335,7 +335,8 @@ private void updateIfChanged(List<String> newList) {
         iterator = iterator();
         currentServerAddr = iterator.next();
 
-        EventDispatcher.fireEvent(new ServerlistChangeEvent());
+        // Using unified event processor, NotifyCenter
+        NotifyCenter.publishEvent(new ServerlistChangeEvent());
         LOGGER.info("[{}] [update-serverlist] serverlist updated to {}", name, serverUrls);
     }
 

client/src/main/java/com/alibaba/nacos/client/config/impl/ServerlistChangeEvent.java

@@ -0,0 +1,27 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * Licensed 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 com.alibaba.nacos.client.config.impl;
+
+import com.alibaba.nacos.common.notify.SlowEvent;
+
+/**
+ * Server List Change Event.
+ *
+ * @author zongtanghu
+ */
+public class ServerlistChangeEvent extends SlowEvent {
+}