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ZooKeeper3.4.10版本Watcher触发关系详解

写操作与读操作函数的Watcher触发关系

在ZooKeeper3.4.10版本中，写操作（create、set、delete）与读操作（exists、getData、getChildren）之间通过Watcher机制建立了特定的触发关系。以下表格详细说明了不同操作对应的事件类型。

详细说明

注意事项

测试代码示例

public class ZooKeeperUtils {
    public static ZooKeeper getZKConn(String hosts) throws IOException {
        int sessionTimeout = 3000;
        System.out.println("连接到ZooKeeper...");
        ZooKeeper zooKeeper = new ZooKeeper(hosts, sessionTimeout, new Watcher() {
            @Override
            public void process(WatchedEvent event) {
                System.out.println("连接事件：" + event.getState());
            }
        });
        System.out.println("连接成功！");
        return zooKeeper;
    }
    public static void testWatcher(String host) throws Exception {
        String path = "/test";
        String pathChild = "/test/test1";
        ZooKeeper zooKeeper = getZKConn(host);
        // 注册"/test"的exists watcher
        Stat stat = zooKeeper.exists(path, new Watcher() {
            @Override
            public void process(WatchedEvent event) {
                System.out.println("exists: " + event.getType());
            }
        });
        if (stat != null) {
            // 注册"/test"的getData watcher
            zooKeeper.getData(path, new Watcher() {
                @Override
                public void process(WatchedEvent event) {
                    System.out.println("getData: " + event.getType());
                }
            }, new Stat());
            // 注册"/test"的getChildren watcher
            zooKeeper.getChildren(path, new Watcher() {
                @Override
                public void process(WatchedEvent event) {
                    System.out.println("getChildren: " + event.getType());
                }
            });
        }
        // 注册"/test/test1"的exists watcher
        Stat statChild = zooKeeper.exists(pathChild, new Watcher() {
            @Override
            public void process(WatchedEvent event) {
                System.out.println("child exists: " + event.getType());
            }
        });
        if (statChild != null) {
            // 注册"/test/test1"的getData watcher
            zooKeeper.getData(pathChild, new Watcher() {
                @Override
                public void process(WatchedEvent event) {
                    System.out.println("child getData: " + event.getType());
                }
            }, new Stat());
            // 注册"/test/test1"的getChildren watcher
            zooKeeper.getChildren(pathChild, new Watcher() {
                @Override
                public void process(WatchedEvent event) {
                    System.out.println("child getChildren: " + event.getType());
                }
            });
        }
        public static void main(String[] args) throws Exception {
            String host = "192.168.56.1:2181";
            testWatcher(host);
            while (true) {
                // 保持连接 alive
            }
        }
    }
}

注意事项

在进行一次写操作之前，需要重新运行程序，因为Watcher只能触发一次。