Watcher机制
pom.xml
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| <dependency>
<groupId>org.apache.zookeeper</groupId>
<artifactId>zookeeper</artifactId>
<version>3.4.6</version>
</dependency>
|
1. 实现Watcher接口
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| package com.fuyi.zk.watcher;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
public class MyWatcher implements Watcher {
public void process(WatchedEvent event) {
System.out.println(event);
}
}
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2. 使用ZooKeeper构造中的默认watcher
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| @Test
public void test1() throws Exception {
//0. 创建watcher
MyWatcher watcher = new MyWatcher();
//1. 在创建ZooKeeper时第三个参数负责设置该zk连接的默认watcher
// 在建立ZooKeeper连接时，就会触发watcher
ZooKeeper zk = new ZooKeeper("localhost:2181", 3000, watcher);
//2. 设置watcher：第二个参数设置true，表示用1步中默认watcher
// 此处可传入watcher实例
Stat stat = zk.exists("/testWatcher", true);
//3. create时 触发
zk.create("/testWatcher", "watcher".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
}
output:
WatchedEvent state:SyncConnected type:None path:null // 创建时输出
WatchedEvent state:SyncConnected type:NodeCreated path:/testWatcher // create时输出
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| @Test
public void test2() throws Exception {
//0. 创建watcher
MyWatcher watcher = new MyWatcher();
//1. 在创建ZooKeeper时第三个参数负责设置该zk连接的默认watcher
// 在建立ZooKeeper连接时，就会触发watcher
ZooKeeper zk = new ZooKeeper("localhost:2181", 3000, watcher);
//2. 创建node
zk.create("/testWatcher", "watcher".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
//3. 设置两个监听，只会收到一个通知
Stat stat = zk.exists("/testWatcher", true);
zk.getData("/testWatcher", true, stat);
//4. 触发通知
zk.setData("/testWatcher", "fuyi".getBytes(), stat.getVersion());
}
output:
WatchedEvent state:SyncConnected type:None path:null // zk创建时输出
WatchedEvent state:SyncConnected type:NodeDataChanged path:/testWatcher //setData()时触发
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| @Test
public void test3() throws Exception {
//0. 创建watcher
MyWatcher watcher = new MyWatcher();
//1. 创建zk
ZooKeeper zk = new ZooKeeper("localhost:2181", 3000, watcher);
//2. 创建/root,只有持久化的节点才能有子节点,此处是持久化节点，
// 多次运行会报节点存在错误,可注掉
//zk.create("/root", "watcher".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
//3. 设置/root节点，的孩子监听
zk.getChildren("/root", true);
//4. 触发/root节点的孩子节点改变事件
zk.create("/root/fuyi", "watcher".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
}
output:
WatchedEvent state:SyncConnected type:None path:null
WatchedEvent state:SyncConnected type:NodeChildrenChanged path:/root
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3. 使用不同watcher实例
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| // 每次调用，获取Watcher实例
private Watcher getInstance(final String msg) {
return new Watcher() {
public void process(WatchedEvent event) {
System.out.println(msg + ": " + event.toString());
}
};
}
@Test
public void test4() throws Exception {
// 0.创建zk
ZooKeeper zk = new ZooKeeper("localhost:2181", 3000, null);
// 1.创建节点
zk.create("/root/fuyi1", "fff".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
// 2.设置监听
Stat stat = zk.exists("/root/fuyi1", getInstance("exists"));
zk.getData("/root/fuyi1", getInstance("getData"), stat);
zk.getChildren("/root", getInstance("getChildren"));
// 3.触发监听
zk.delete("/root/fuyi1", stat.getVersion());
}
output:
getData: WatchedEvent state:SyncConnected type:NodeDeleted path:/root/fuyi1
exists: WatchedEvent state:SyncConnected type:NodeDeleted path:/root/fuyi1
getChildren: WatchedEvent state:SyncConnected type:NodeChildrenChanged path:/root
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上例中由于exists和getData分别设置了两个不同的Watcher实例，所以虽然watcher都是由同了一个NodeDataChanged触发的，但exists()和getData()都会收到通知。由于创建Zookeeper时没有设置watcher(参数为null)，所以建立连接时没有收到通知。