【Apache ZooKeeper】为ZNode设置watcher

       众所周知，ZooKeeper中的ZNode是树形结构，现在我需要给/app1结点设置watcher，监听/app1下增减、删除和修改的结点，并将相应的事件使用log4j记录到日志文件中。ZNode的变化可以直接通过event.getType来获取。使用zk.exists(PATH, wc);来为PATH结点设置watcher，所有结点都可以使用wc做watcher。 

       代码如下：

package com.iflytek.cpcloud.zookeeper;



import java.io.IOException;

import java.util.List;



import org.apache.commons.logging.Log;

import org.apache.commons.logging.LogFactory;

import org.apache.log4j.PropertyConfigurator;

import org.apache.zookeeper.KeeperException;

import org.apache.zookeeper.WatchedEvent;

import org.apache.zookeeper.Watcher;

import org.apache.zookeeper.ZooKeeper;

import org.apache.zookeeper.Watcher.Event.EventType;



public class WatchClient implements Runnable {



	private static final Log LOG = LogFactory.getLog(WatchClient.class);

	public static final int CLIENT_PORT = 2181;

	public static final String PATH = "/app1";// 所要监控的结点

	private static ZooKeeper zk;

	private static List<String> nodeList;// 所要监控的结点的子结点列表



	public static void main(String[] args) throws Exception {

		PropertyConfigurator.configure("F:\\test\\conf\\log4j.properties");

		WatchClient client = new WatchClient();

		Thread th = new Thread(client);

		th.start();

	}



	public WatchClient() throws IOException {



		zk = new ZooKeeper("192.168.255.133:" + CLIENT_PORT, 21810,

				new Watcher() {

					public void process(WatchedEvent event) {

					}

				});

	}



	/**

	 * 设置watch的线程

	 */

	@Override

	public void run() {

		

		Watcher wc = new Watcher() {

			@Override

			public void process(WatchedEvent event) {

				// 结点数据改变之前的结点列表

				List<String> nodeListBefore = nodeList;

				// 主结点的数据发生改变时

				if (event.getType() == EventType.NodeDataChanged) {

					LOG.info("Node data changed:" + event.getPath());

				}

				if (event.getType() == EventType.NodeDeleted){

					LOG.info("Node deleted:" + event.getPath());

				}

				if(event.getType()== EventType.NodeCreated){

					LOG.info("Node created:"+event.getPath());

				}



				// 获取更新后的nodelist

				try {

					nodeList = zk.getChildren(event.getPath(), false);

				} catch (KeeperException e) {

					System.out.println(event.getPath()+" has no child, deleted.");

				} catch (InterruptedException e) {

					e.printStackTrace();

				}

				List<String> nodeListNow = nodeList;

				// 增加结点

				if (nodeListBefore.size() < nodeListNow.size()) {

					for (String str : nodeListNow) {

						if (!nodeListBefore.contains(str)) {

							LOG.info("Node created:" + event.getPath() + "/" + str);

						}

					}

				}

			}

		};



		/**

		 * 持续监控PATH下的结点

		 */

		while (true) {

			try {

				zk.exists(PATH, wc);//所要监控的主结点

			} catch (KeeperException | InterruptedException e) {

				e.printStackTrace();

			}

			try {

				nodeList = zk.getChildren(PATH, wc);

			} catch (KeeperException | InterruptedException e) {

				e.printStackTrace();

			}

			// 对PATH下的每个结点都设置一个watcher



			for (String nodeName : nodeList) {

				try {

					zk.exists(PATH + "/" + nodeName, wc);

				} catch (KeeperException | InterruptedException e) {

					e.printStackTrace();

				}

			}

			

			try {

				Thread.sleep(3000);// sleep一会，减少CUP占用率

			} catch (InterruptedException e) {

				e.printStackTrace();

			}

		}

	}

}

该项目使用maven构建。pom.xml文件如下：

 

<?xml version="1.0" encoding="UTF-8"?>



<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">



  <modelVersion>4.0.0</modelVersion>



  <groupId>com.iflytek.cpcloud</groupId>

  <artifactId>zookeeper-test</artifactId>

  <version>0.1.0-SNAPSHOT</version>



  <dependencies>

    <dependency>

      <groupId>log4j</groupId>

      <artifactId>log4j</artifactId>

      <version>1.2.17</version>

    </dependency>

    <dependency>

      <groupId>commons-logging</groupId>

      <artifactId>commons-logging</artifactId>

      <version>1.1.1</version>

    </dependency>

    <dependency>

      <groupId>commons-cli</groupId>

      <artifactId>commons-cli</artifactId>

      <version>1.2</version>

    </dependency>

    <dependency>

      <groupId>junit</groupId>

      <artifactId>junit</artifactId>

      <version>4.11</version>

    </dependency>

	<dependency>

      <groupId>org.apache.zookeeper</groupId>

      <artifactId>zookeeper</artifactId>

      <version>3.4.5</version>

    </dependency>

  </dependencies>



  <build>

    <plugins>

      <plugin>

	<artifactId>maven-assembly-plugin</artifactId>

	<version>2.2-beta-5</version>

	<configuration>

	  <descriptorRefs>

	    <descriptorRef>jar-with-dependencies</descriptorRef>

	  </descriptorRefs>

	</configuration>

      </plugin>

      <plugin>

	<groupId>org.apache.maven.plugins</groupId>

	<artifactId>maven-compiler-plugin</artifactId>

	<version>2.3.2</version>

	<configuration>

	  <source>1.6</source>

	  <target>1.6</target>

	  <encoding>UTF-8</encoding>

	</configuration>

      </plugin>

    </plugins>

  </build>



</project>