Merge pull request #73 from allenxwang/cp

Added the functionality to notify listeners when server list is changed from BaseLoadBalancer.

ribbon-core/src/main/java/com/netflix/loadbalancer/BaseLoadBalancer.java

@@ -23,6 +23,7 @@ import java.util.Comparator;
 import java.util.List;
 import java.util.Timer;
 import java.util.TimerTask;
+import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.locks.Lock;
 import java.util.concurrent.locks.ReadWriteLock;
@@ -31,6 +32,7 @@ import java.util.concurrent.locks.ReentrantReadWriteLock;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import com.google.common.collect.ImmutableList;
 import com.netflix.client.ClientFactory;
 import com.netflix.client.IClientConfigAware;
 import com.netflix.client.PrimeConnections;
@@ -92,6 +94,8 @@ public class BaseLoadBalancer extends AbstractLoadBalancer implements
     private volatile boolean enablePrimingConnections = false;
     
     private IClientConfig config;
+    
+    private List<ServerListChangeListener> changeListeners = new CopyOnWriteArrayList<ServerListChangeListener>();
 
     /**
      * Default constructor which sets name as "default", sets null ping, and
@@ -203,6 +207,14 @@ public class BaseLoadBalancer extends AbstractLoadBalancer implements
         init();
     }
 
+    public void addServerListChangeListener(ServerListChangeListener listener) {
+        changeListeners.add(listener);
+    }
+    
+    public void removeServerListChangeListener(ServerListChangeListener listener) {
+        changeListeners.remove(listener);
+    }
+
     public IClientConfig getClientConfig() {
     	return config;
     }
@@ -468,6 +480,17 @@ public class BaseLoadBalancer extends AbstractLoadBalancer implements
             boolean listChanged = false;
             if (!allServerList.equals(allServers)) {
                 listChanged = true;
+                if (changeListeners != null && changeListeners.size() > 0) {
+                   List<Server> oldList = ImmutableList.copyOf(allServerList);
+                   List<Server> newList = ImmutableList.copyOf(allServers);                   
+                   for (ServerListChangeListener l: changeListeners) {
+                       try {
+                           l.serverListChanged(oldList, newList);
+                       } catch (Throwable e) {
+                           logger.error("Error invoking server list change listener", e);
+                       }
+                   }
+                }
             }
             if (isEnablePrimingConnections()) {
                 for (Server server : allServers) {

ribbon-core/src/main/java/com/netflix/loadbalancer/ServerListChangeListener.java

+/*
+ *
+ * Copyright 2014 Netflix, Inc.
+ *
+ * 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.netflix.loadbalancer;
+
+import java.util.List;
+
+public interface ServerListChangeListener {
+    /**
+     * Invoked by {@link BaseLoadBalancer} when server list is changed  
+     */
+    public void serverListChanged(List<Server> oldList, List<Server> newList);
+}

ribbon-core/src/test/java/com/netflix/loadbalancer/ServerListChangeListenerTest.java

+/*
+ *
+ * Copyright 2014 Netflix, Inc.
+ *
+ * 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.netflix.loadbalancer;
+
+import static org.junit.Assert.*;
+
+import java.util.List;
+
+import org.junit.Test;
+
+import com.google.common.collect.Lists;
+
+public class ServerListChangeListenerTest {
+
+    private volatile List<Server> oldList;
+    private volatile List<Server> newList;
+    
+    @Test
+    public void testListener() {
+        BaseLoadBalancer lb = new BaseLoadBalancer();
+        lb.addServerListChangeListener(new ServerListChangeListener() {
+            @Override
+            public void serverListChanged(List<Server> oldList, List<Server> newList) {
+                ServerListChangeListenerTest.this.oldList = oldList;
+                ServerListChangeListenerTest.this.newList = newList;
+            }
+        });
+        List<Server> list1 = Lists.newArrayList(new Server("www.google.com:80"), new Server("www.netflix.com:80"));
+        List<Server> list2 = Lists.newArrayList(new Server("www.microsoft.com:80"), new Server("www.facebook.com:80"));
+        lb.setServersList(list1);
+        assertTrue(oldList.isEmpty());
+        assertEquals(list1, newList);
+        lb.setServersList(list2);
+        assertEquals(list1, oldList);
+        assertEquals(list2, newList);
+    }
+}