Zookeeper客户端API之读取子节点内容（九）

朴灿烈づ我的快乐病毒、 2021-09-14 20:26 321阅读 0赞

[http://blog.csdn.net/wo541075754/article/details/66967706][http_blog.csdn.net_wo541075754_article_details_66967706]

本篇博客介绍一下Zookeeper原声API读取节点内容的使用方法。

## 读取节点内容方法介绍 ##

### 方法 ###

Zookeeper提供了两个方法来获取节点内容，同步获取和异步获取：

public byte[] getData(String path, boolean watch, Stat stat)
     
      
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public void getData(final String path, Watcher watcher,
                DataCallback cb, Object ctx)
     
      
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### 参数说明 ###

<table style="width:908px; border-collapse:collapse; border-spacing:0px; border:1px solid rgb(238,238,238); color:rgb(63,63,63); font-family:&quot;microsoft yahei&quot;; font-size:16px"> 
 <thead style=""> 
  <tr style=""> 
   <th style="padding:8px; line-height:20px; vertical-align:top; border:1px solid rgb(238,238,238)"> 参数</th> 
   <th align="left" style="padding:8px; line-height:20px; vertical-align:top; border:1px solid rgb(238,238,238)"> 说明</th> 
  </tr> 
 </thead> 
 <tbody style=""> 
  <tr style=""> 
   <td style="padding:8px; line-height:20px; vertical-align:top; border:1px solid rgb(238,238,238)"> path</td> 
   <td align="left" style="padding:8px; line-height:20px; vertical-align:top; border:1px solid rgb(238,238,238)"> 指定数据节点的路径，获取该节点下面的子节点</td> 
  </tr> 
  <tr style=""> 
   <td style="padding:8px; line-height:20px; vertical-align:top; border:1px solid rgb(238,238,238)"> watcher</td> 
   <td align="left" style="padding:8px; line-height:20px; vertical-align:top; border:1px solid rgb(238,238,238)"> 注册在path上的Watcher。节点变更会通知会向客户端发起通知。</td> 
  </tr> 
  <tr style=""> 
   <td style="padding:8px; line-height:20px; vertical-align:top; border:1px solid rgb(238,238,238)"> stat</td> 
   <td align="left" style="padding:8px; line-height:20px; vertical-align:top; border:1px solid rgb(238,238,238)"> 指定数据节点状态信息。传入旧stat，方法执行过程中会将其替换为新stat对象。</td> 
  </tr> 
  <tr style=""> 
   <td style="padding:8px; line-height:20px; vertical-align:top; border:1px solid rgb(238,238,238)"> watch</td> 
   <td align="left" style="padding:8px; line-height:20px; vertical-align:top; border:1px solid rgb(238,238,238)"> 表示是否需要注册一个watcher。true：注册默认watcher，false：不需要注册watcher</td> 
  </tr> 
  <tr style=""> 
   <td style="padding:8px; line-height:20px; vertical-align:top; border:1px solid rgb(238,238,238)"> cb</td> 
   <td align="left" style="padding:8px; line-height:20px; vertical-align:top; border:1px solid rgb(238,238,238)"> 注册一个异步回调函数</td> 
  </tr> 
  <tr style=""> 
   <td style="padding:8px; line-height:20px; vertical-align:top; border:1px solid rgb(238,238,238)"> ctx</td> 
   <td align="left" style="padding:8px; line-height:20px; vertical-align:top; border:1px solid rgb(238,238,238)"> 传递上下文信息</td> 
  </tr> 
 </tbody> 
</table>

## 具体案例 ##

### 同步方法 ###

package com.secbro.learn;
    
    import org.apache.zookeeper.*;
    import org.apache.zookeeper.data.Stat;
    
    import java.util.concurrent.CountDownLatch;
    
    /** * 读取节点数据 * Created by zhuzs on 2017/3/27. */
    public class TestGetData implements Watcher{ 
        private static CountDownLatch countDownLatch = new CountDownLatch(1);
    
        private static ZooKeeper zooKeeper;
        private static Stat stat = new Stat();
    
        public static void main(String[] args) throws Exception{
            zooKeeper = new ZooKeeper("127.0.0.1:2181", 5000, new TestGetData());
            countDownLatch.await();
    
            String path = "/test-get-data";
            zooKeeper.create(path,"123".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
    
            System.out.println("同步读取节点内容：" + new String(zooKeeper.getData(path,true,stat)));
            System.out.println("同步读取Stat：czxid=" + stat.getCzxid()
                    + ";mzxid=" + stat.getMzxid() + ";version="  + stat.getVersion());
    
            zooKeeper.setData(path,"123".getBytes(),-1);
            Thread.sleep(10000);
        }
    
        public void process(WatchedEvent event) {
            if (Event.KeeperState.SyncConnected == event.getState()) {
                if(Event.EventType.None == event.getType() && null == event.getPath()){ // 连接时的监听事件
                    countDownLatch.countDown();
                } else if (event.getType() == Event.EventType.NodeDataChanged){ // 子节点内容变更时的监听
                    try {
                        System.out.println("监听获得通知内容：data="
                                + new String(zooKeeper.getData(event.getPath(),true,stat)));
                        System.out.println("监听获得通知Stat：czxid=" + stat.getCzxid()
                                + ";mzxid=" + stat.getMzxid() + ";version="  + stat.getVersion());
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            }
        }
    }
     
      
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运行结果：

同步读取节点内容：123
    同步读取Stat：czxid=14700;mzxid=14700;version=0
    监听获得通知内容：data=123
    监听获得通知Stat：czxid=14700;mzxid=14701;version=1
     
      
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代码的基本逻辑为创建一个临时节点，然后读取临时节点内容，并注册监听，当节点变化（内容变化或版本信息变化），触发监听事件，获取最新的节点信息。

### 异步方法 ###

package com.secbro.learn;
    
    import org.apache.zookeeper.*;
    import org.apache.zookeeper.data.Stat;
    
    import java.util.concurrent.CountDownLatch;
    
    /** * 读取节点数据 * Created by zhuzs on 2017/3/27. */
    public class TestGetData implements Watcher{ 
        private static CountDownLatch countDownLatch = new CountDownLatch(1);
    
        private static ZooKeeper zooKeeper;
        private static Stat stat = new Stat();
    
        public static void main(String[] args) throws Exception{
            zooKeeper = new ZooKeeper("127.0.0.1:2181", 5000, new TestGetData());
            countDownLatch.await();
    
            String path = "/test-get-data";
            zooKeeper.create(path,"123".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
            // 异步读取节点内容
            zooKeeper.getData(path,true,new MyDataCallback(),null);
    
            zooKeeper.setData(path,"123".getBytes(),-1);
    
            Thread.sleep(10000);
        }
    
        public void process(WatchedEvent event) {
            if (Event.KeeperState.SyncConnected == event.getState()) {
                if(Event.EventType.None == event.getType() && null == event.getPath()){ // 连接时的监听事件
                    countDownLatch.countDown();
                } else if (event.getType() == Event.EventType.NodeDataChanged){ // 子节点内容变更时的监听
                    try {
                        System.out.println("监听获得通知内容：data="
                                + new String(zooKeeper.getData(event.getPath(),true,stat)));
                        System.out.println("监听获得通知Stat：czxid=" + stat.getCzxid()
                                + ";mzxid=" + stat.getMzxid() + ";version="  + stat.getVersion());
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            }
        }
    }
    
    class MyDataCallback implements AsyncCallback.DataCallback{
    
        public void processResult(int rc, String path, Object ctx, byte[] data, Stat stat) {
            System.out.println("异步返回结果：rc=" + rc + ";path=" + path + ";data=" + new String(data));
            System.out.println("异步读取Stat：czxid=" + stat.getCzxid()
                    + ";mzxid=" + stat.getMzxid() + ";version="  + stat.getVersion());
        }
    }
    
     
      
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运行结果：

异步返回结果：rc=0;path=/test-get-data;data=123
    异步读取Stat：czxid=14704;mzxid=14704;version=0
    监听获得通知内容：data=123
    监听获得通知Stat：czxid=14704;mzxid=14705;version=1
     
      
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异步方法与同步方法业务逻辑基本相同，区别点在于将同步获取改为异步获取。

[http_blog.csdn.net_wo541075754_article_details_66967706]: http://blog.csdn.net/wo541075754/article/details/66967706