Curator Cache

1.Curator Cache 與原生ZooKeeper Wacher差別

原生的ZooKeeper Wacher是一次性的：一個Wacher一旦觸發就會被移出，如果你想要反複使用Wacher，就要在Wacher被移除後重新注冊，使用起來很麻煩。使用Curator Cache 可以反複使用Wacher了。

2.Curator Cache 和Curator Wacher差別

2.相關類

Curator Cache主要提供了一下三組類，分别用于實作對節點的監聽，子節點的監聽和二者的混合：

1.NodeCache,NodeCacheListener，ChildData，節點建立，節點資料内容變更，不能監聽節點删除。

2.PathChildrenCache，PathChildrenCacheListener，PathChildrenCacheEvent監聽指定節點的子節點的變更包括添加，删除，子節點資料資料變更這三類。

3.TreeCache，TreeCacheListener，TreeCacheEvent，TreeCacheSelector

3.節點監聽

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{
    
         
          //這裡因為是測試，沒有加他們。
          //CloseableUtils.closeQuietly(nodeCache);
         /// CloseableUtils.closeQuietly(client);
         // CloseableUtils.closeQuietly(server);
      }     
  }
  
  public static void addListener(NodeCache nodeCache){
      //監聽類型：節點是否存在，節點資料内容改變，不監聽節點删除。
         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()));
                
            }});
  }
}

在上面的代碼中首先建立了一個節點，然後建立用這個節點路徑來建立NodeCache，啟動NodeCache，添加NodeCacheListener。然後調用setData來修改節點資料。上面的代碼輸入如下：

path:/francis/nodecache/_c_d5be73ca-592c-4eda-b7c4-c8ec60ef39a8-a,data:hello

子節點監聽：

PathChildrenCache的構造函數如下：

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，如果為true，那麼當對子節點調用setData時，PathChildrenCache會受到這個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();
         
         //這裡将第三個參數cacheData設定為true，這樣當對子節點調用setData時，會受到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()));
               }
              
            }});
         
         //建立父節點
         System.out.println(client.create().creatingParentsIfNeeded().withMode(CreateMode.PERSISTENT).forPath(path,"init".getBytes()));
         Thread.sleep(1000);
         
         //建立子節點
         String childPath1=ZKPaths.makePath(path, "a");
         childPath1=client.create().withMode(CreateMode.PERSISTENT).forPath(childPath1,"1".getBytes());
         Thread.sleep(1000);
         
         //對子節點指派
         client.setData().forPath(childPath1,"aaa".getBytes());
         Thread.sleep(1000);
         
         //删除子節點
         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功能結合到一起了。他不僅可以對子節點和父節點同時進行監聽。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());
                }
           }
             
         });
         
         

         
         //建立父節點
         client.create().creatingParentsIfNeeded().withMode(CreateMode.PERSISTENT).forPath(path,"init".getBytes());
         Thread.sleep(1000);
         
         //建立子節點
         String childPath1=ZKPaths.makePath(path, "a");
         childPath1=client.create().withMode(CreateMode.PERSISTENT).forPath(childPath1,"1".getBytes());
         Thread.sleep(1000);
         
         //對子節點指派
         client.setData().forPath(childPath1,"aaa".getBytes());
         Thread.sleep(1000);

         //對子節點指派
         client.setData().forPath(path,"aaa".getBytes());
         Thread.sleep(1000);

         //删除子節點
         client.delete().forPath(childPath1);
         client.delete().deletingChildrenIfNeeded().forPath("/francis");
         
        
         Thread.sleep(2000);
         
      }catch(Exception e){
          e.printStackTrace();
      }finally{
    
         
          //這裡因為是測試，沒有加他們。
          CloseableUtils.closeQuietly(nodeCache);
          CloseableUtils.closeQuietly(client);
          CloseableUtils.closeQuietly(server);
      }     
  }
}

輸出如下：

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

Curator Cache

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