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(){

            @Override

            public void nodeChanged() throws Exception {

                // TODO Auto-generated method stub

                if(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(){

            @Override

            public void childEvent(CuratorFramework client, PathChildrenCacheEvent event) throws Exception {

                // TODO Auto-generated method stub

               if(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(){

            @Override

            public void childEvent(CuratorFramework client, TreeCacheEvent event) throws Exception {

                // TODO Auto-generated method stub

                switch(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

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