1.Curator Cache 与原生ZooKeeper Wacher区别
原生的ZooKeeper Wacher是一次性的：一个Wacher一旦触发就会被移出，如果你想要反复使用Wacher，就要在Wacher被移除后重新注册，使用起来很麻烦。使用Curator Cache 可以反复使用Wacher了。
2.Curator Cache 和Curator Wacher区别
2.相关类
Curator Cache主要提供了一下三组类，分别用于实现对节点的监听，子节点的监听和二者的混合：
1.NodeCache,NodeCacheListener，ChildData，节点创建，节点数据内容变更，不能监听节点删除。
2.PathChildrenCache，PathChildrenCacheListener，PathChildrenCacheEvent监听指定节点的子节点的变更包括添加，删除，子节点数据数据变更这三类。
3.TreeCache，TreeCacheListener，TreeCacheEvent，TreeCacheSelector
3.节点监听
package cn.francis.maven.hello.ZooKeeper;import org.apache.curator.framework.CuratorFramework; import org.apache.curator.framework.CuratorFrameworkFactory; import org.apache.curator.framework.recipes.cache.NodeCache; import org.apache.curator.framework.recipes.cache.NodeCacheListener; import org.apache.curator.framework.recipes.cache.TreeCache; import org.apache.curator.retry.ExponentialBackoffRetry; import org.apache.curator.test.TestingServer; import org.apache.curator.utils.CloseableUtils; import org.apache.zookeeper.CreateMode;public class NodeCacheDemo {public static void main(String[]args) throws Exception{TestingServer server=null;CuratorFramework client=null;NodeCache nodeCache=null;String path="/francis/nodecache/a";try{ server=new TestingServer();client= CuratorFrameworkFactory.newClient(server.getConnectString(), new ExponentialBackoffRetry(1000,3));client.start();path=client.create().creatingParentsIfNeeded().withProtection().withMode(CreateMode.EPHEMERAL).forPath(path,"init".getBytes());nodeCache=new NodeCache(client,path,false);nodeCache.start();addListener(nodeCache);client.setData().forPath(path,"hello".getBytes());Thread.sleep(1000);client.delete().deletingChildrenIfNeeded().forPath(path);Thread.sleep(Integer.MAX_VALUE);}catch(Exception e){e.printStackTrace();}finally{//这里因为是测试，没有加他们。//CloseableUtils.closeQuietly(nodeCache);/// CloseableUtils.closeQuietly(client);// CloseableUtils.closeQuietly(server); } }public static void addListener(NodeCache nodeCache){//监听类型：节点是否存在，节点数据内容改变，不监听节点删除。nodeCache.getListenable().addListener(new NodeCacheListener(){@Overridepublic void nodeChanged() throws Exception {// TODO Auto-generated method stubif(nodeCache.getCurrentData()!=null)System.out.println("path:"+nodeCache.getCurrentData().getPath()+",data:"+new String(nodeCache.getCurrentData().getData()));}});} }
在上面的代码中首先创建了一个节点，然后创建用这个节点路径来创建NodeCache，启动NodeCache，添加NodeCacheListener。然后调用setData来修改节点数据。上面的代码输入如下：
path:/francis/nodecache/_c_d5be73ca-592c-4eda-b7c4-c8ec60ef39a8-a,data:hello
子节点监听：
PathChildrenCache的构造函数如下：
public PathChildrenCache(CuratorFramework client,String path,boolean cacheData) Parameters: client - the client path - path to watch cacheData - if true, node contents are cached in addition to the stat
其中最主要的是cacheData，如果为true，那么当对子节点调用setData时，PathChildrenCache会受到这个CHILD_UPDATED事件。
下面看一下demo：
package cn.francis.maven.hello.ZooKeeper;import org.apache.curator.framework.CuratorFramework; import org.apache.curator.framework.CuratorFrameworkFactory; import org.apache.curator.framework.recipes.cache.NodeCache; import org.apache.curator.framework.recipes.cache.NodeCacheListener; import org.apache.curator.framework.recipes.cache.PathChildrenCache; import org.apache.curator.framework.recipes.cache.PathChildrenCache.StartMode; import org.apache.curator.framework.recipes.cache.PathChildrenCacheEvent; import org.apache.curator.framework.recipes.cache.PathChildrenCacheListener; import org.apache.curator.framework.recipes.cache.TreeCache; import org.apache.curator.framework.recipes.cache.PathChildrenCacheEvent.Type; import org.apache.curator.retry.ExponentialBackoffRetry; import org.apache.curator.test.TestingServer; import org.apache.curator.utils.CloseableUtils; import org.apache.curator.utils.ZKPaths; import org.apache.hadoop.mapred.join.Parser.TType; import org.apache.zookeeper.CreateMode;public class NodeCacheDemo {public static void main(String[]args) throws Exception{TestingServer server=null;CuratorFramework client=null;NodeCache nodeCache=null;String path="/francis/nodecache/b";try{ server=new TestingServer();client= CuratorFrameworkFactory.newClient(server.getConnectString(),new ExponentialBackoffRetry(1000,3));client.start();//这里将第三个参数cacheData设置为true，这样当对子节点调用setData时，会受到CHILDREN_UPDATE通知。PathChildrenCache childrenCache=new PathChildrenCache(client,path,true);
childrenCache.start(StartMode.POST_INITIALIZED_EVENT);childrenCache.getListenable().addListener(new PathChildrenCacheListener(){@Overridepublic void childEvent(CuratorFramework client, PathChildrenCacheEvent event) throws Exception {// TODO Auto-generated method stubif(event.getType()==Type.INITIALIZED){System.out.println("create"+event.getData().getPath()); }else if(event.getType()==Type.CHILD_ADDED){System.out.println("create"+event.getData().getPath()); }else if(event.getType()==Type.CHILD_REMOVED){System.out.println("remove:"+event.getData().getPath());}else if(event.getType()==Type.CHILD_UPDATED){//System.out.println("update:"+event.getData().getPath());System.out.println("update:"+new String(event.getData().getData()));}}});//创建父节点System.out.println(client.create().creatingParentsIfNeeded().withMode(CreateMode.PERSISTENT).forPath(path,"init".getBytes()));Thread.sleep(1000);//创建子节点String childPath1=ZKPaths.makePath(path, "a");childPath1=client.create().withMode(CreateMode.PERSISTENT).forPath(childPath1,"1".getBytes());Thread.sleep(1000);//对子节点赋值client.setData().forPath(childPath1,"aaa".getBytes());Thread.sleep(1000);//删除子节点 client.delete().forPath(childPath1);client.delete().deletingChildrenIfNeeded().forPath("/francis");Thread.sleep(2000);}catch(Exception e){e.printStackTrace();}finally{ CloseableUtils.closeQuietly(nodeCache);CloseableUtils.closeQuietly(client);CloseableUtils.closeQuietly(server);} }
3.TreeNodeCache
TreeNodeCache将NodeCache和PathChildrenCache功能结合到一起了。他不仅可以对子节点和父节点同时进行监听。如下：
package cn.francis.maven.hello.ZooKeeper;import java.util.Map;import org.apache.curator.framework.CuratorFramework; import org.apache.curator.framework.CuratorFrameworkFactory; import org.apache.curator.framework.recipes.cache.ChildData; import org.apache.curator.framework.recipes.cache.NodeCache; import org.apache.curator.framework.recipes.cache.NodeCacheListener; import org.apache.curator.framework.recipes.cache.PathChildrenCache; import org.apache.curator.framework.recipes.cache.PathChildrenCache.StartMode; import org.apache.curator.framework.recipes.cache.PathChildrenCacheEvent; import org.apache.curator.framework.recipes.cache.PathChildrenCacheListener; import org.apache.curator.framework.recipes.cache.TreeCache; import org.apache.curator.framework.recipes.cache.TreeCacheEvent; import org.apache.curator.framework.recipes.cache.TreeCacheListener; import org.apache.curator.framework.recipes.cache.PathChildrenCacheEvent.Type; import org.apache.curator.retry.ExponentialBackoffRetry; import org.apache.curator.test.TestingServer; import org.apache.curator.utils.CloseableUtils; import org.apache.curator.utils.ZKPaths; import org.apache.hadoop.mapred.join.Parser.TType; import org.apache.zookeeper.CreateMode;public class NodeCacheDemo {public static void main(String[]args) throws Exception{TestingServer server=null;CuratorFramework client=null;NodeCache nodeCache=null;String path="/francis/nodecache/b";try{ server=new TestingServer();client= CuratorFrameworkFactory.newClient(server.getConnectString(),new ExponentialBackoffRetry(1000,3));client.start();TreeCache treeNodeCache=new TreeCache(client,path);treeNodeCache.start();treeNodeCache.getListenable().addListener(new TreeCacheListener(){@Overridepublic void childEvent(CuratorFramework client, TreeCacheEvent event) throws Exception {// TODO Auto-generated method stubswitch(event.getType()){case NODE_ADDED:System.out.println("added:"+event.getData().getPath());break;case NODE_UPDATED:System.out.println("updated:"+event.getData().getPath());break;case NODE_REMOVED: System.out.println("removed:"+event.getData().getPath());break;default:System.out.println("other:"+event.getType());}}});//创建父节点client.create().creatingParentsIfNeeded().withMode(CreateMode.PERSISTENT).forPath(path,"init".getBytes());Thread.sleep(1000);//创建子节点String childPath1=ZKPaths.makePath(path, "a");childPath1=client.create().withMode(CreateMode.PERSISTENT).forPath(childPath1,"1".getBytes());Thread.sleep(1000);//对子节点赋值client.setData().forPath(childPath1,"aaa".getBytes());Thread.sleep(1000);//对子节点赋值client.setData().forPath(path,"aaa".getBytes());Thread.sleep(1000);//删除子节点 client.delete().forPath(childPath1);client.delete().deletingChildrenIfNeeded().forPath("/francis");Thread.sleep(2000);}catch(Exception e){e.printStackTrace();}finally{//这里因为是测试，没有加他们。 CloseableUtils.closeQuietly(nodeCache);CloseableUtils.closeQuietly(client);CloseableUtils.closeQuietly(server);} } }
输出如下：
other:INITIALIZED
added:/francis/nodecache/b
added:/francis/nodecache/b/a
updated:/francis/nodecache/b/a
updated:/francis/nodecache/b
removed:/francis/nodecache/b/a
removed:/francis/nodecache/b
