读《分布式一致性原理》JAVA客户端API操作

创建会话

客户端可以通过创建一个Zookeeper实例来连接服务器。4种构造方法如下

ZooKeeper(connectString, sessionTimeout, watcher)；

ZooKeeper(String connectString, int sessionTimeout, Watcher watcher, boolean canBeReadOnly)

 ZooKeeper(String connectString, int sessionTimeout, Watcher watcher,long sessionId, byte[] sessionPasswd)；

ZooKeeper(String connectString, int sessionTimeout, Watcher watcher,long sessionId, byte[] sessionPasswd, boolean canBeReadOnly)

注意，zookeeper客户端和服务端会话建立是一个异步的过程，也是就是说在程序中构造zookeeper方法初始化方法执行完后

会立即返回，在大多数情况下此时并没有真正的建立一个可用的会话，此时会话正处于CONnectioning状态。当真正的会话建立后

服务端会向客户端发送一个通知，客户端在获取这个通知后会话才真正的建立。

package session;

import java.io.IOException;

import java.util.concurrent.CountDownLatch;

import org.apache.zookeeper.WatchedEvent;

import org.apache.zookeeper.Watcher;

import org.apache.zookeeper.ZooKeeper;

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

public class CreateZookeeper implements Watcher {

    private static CountDownLatch connectedSemaphore = new CountDownLatch(1);

    @Override

    public void process(WatchedEvent event) {

        System.out.println("receive watched event:"+event);

        if (KeeperState.SyncConnected==event.getState()) {

            connectedSemaphore.countDown();

        }

    }

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

        ZooKeeper zooKeeper = new ZooKeeper("192.168.64.60", 5000, new CreateZookeeper());

        System.out.println(zooKeeper.getState());

        try {

            connectedSemaphore.await();

        } catch (InterruptedException e) {}

            System.out.println("zookeeper session established");

    }

}

程序运行结果如下：

CreateZookeeper类实现了Watcher接口重写了process方法，该方法负责处理来自zookeeper服务端的通知。在

收到来自服务端的synconncted事件后，解除了主程序中的CountDownLatch等待阻塞。至此客户端会话创建完成。

创建一个复用sessionId和sessionPasswd的实例

package session;

import java.io.IOException;

import java.util.concurrent.CountDownLatch;

import org.apache.zookeeper.WatchedEvent;

import org.apache.zookeeper.Watcher;

import org.apache.zookeeper.ZooKeeper;

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

public class CreateZookeeper2 implements Watcher {

public static CountDownLatch connectedSemaphore = new CountDownLatch(1);

@Override

public void process(WatchedEvent event) {

    System.out.println("receive watched event:"+event);

    if (KeeperState.SyncConnected==event.getState()) {

        connectedSemaphore.countDown();

    }

}

public static void main(String[] args) throws IOException, InterruptedException {

    ZooKeeper zooKeeper = new ZooKeeper("192.168.64.60", 5000, new CreateZookeeper());

    connectedSemaphore.await();

    long sessionId = zooKeeper.getSessionId();

    byte[] sessionPasswd = zooKeeper.getSessionPasswd();

    //复用sessionId和sessionPasswd

     zooKeeper = new ZooKeeper("192.168.64.60", 5000, new CreateZookeeper(),1l,"test".getBytes());

     zooKeeper = new ZooKeeper("192.168.64.60", 5000, new CreateZookeeper(),sessionId,sessionPasswd);

     Thread.sleep(Integer.MAX_VALUE);

}

}

我们可以看出，第一次使用错误的id和pw服务端返回“EXpired”事件，而第二次使用正确的id和pw则重新连接上。

巴特西

读《分布式一致性原理》JAVA客户端API操作

创建会话

创建一个复用sessionId和sessionPasswd的实例

最新文章

热门文章