Polish spring-cloud-incubator/spring-cloud-alibaba#623 : Adapter Nacos implementation

spring-cloud-alibaba-dubbo/src/main/java/com/alibaba/cloud/dubbo/registry/event/SubscribedServicesChangedEvent.java

@@ -0,0 +1,65 @@
+/*
+ * 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 com.alibaba.cloud.dubbo.registry.event;
+
+import org.springframework.context.ApplicationEvent;
+
+import java.util.LinkedHashSet;
+import java.util.Objects;
+import java.util.Set;
+
+/**
+ * {@link ApplicationEvent Event} raised when the subscribed services are changed
+ * <p>
+ *
+ * @author <a href="mailto:mercyblitz@gmail.com">Mercy</a>
+ * @see ApplicationEvent
+ */
+public class SubscribedServicesChangedEvent extends ApplicationEvent {
+
+    private final Set<String> oldSubscribedServices;
+
+    private final Set<String> newSubscribedServices;
+
+    private final boolean changed;
+
+    /**
+     * Create a new ApplicationEvent.
+     *
+     * @param source                the object on which the event initially occurred (never {@code null})
+     * @param oldSubscribedServices the subscribed services before changed
+     * @param newSubscribedServices the subscribed services after changed
+     */
+    public SubscribedServicesChangedEvent(Object source, Set<String> oldSubscribedServices, Set<String> newSubscribedServices) {
+        super(source);
+        this.oldSubscribedServices = new LinkedHashSet<>(oldSubscribedServices);
+        this.newSubscribedServices = new LinkedHashSet<>(newSubscribedServices);
+        this.changed = !Objects.equals(oldSubscribedServices, newSubscribedServices);
+    }
+
+    public Set<String> getOldSubscribedServices() {
+        return oldSubscribedServices;
+    }
+
+    public Set<String> getNewSubscribedServices() {
+        return newSubscribedServices;
+    }
+
+    public boolean isChanged() {
+        return changed;
+    }
+}