本文主要是介绍【Apache ZooKeeper】为ZNode设置watcher，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
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*/@Overridepublic void run() {Watcher wc = new Watcher() {@Overridepublic 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nodelisttry {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watcherfor (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>
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