连接zookeeper集群

连接到ZooKeeper集合

ZooKeeper类通过其构造函数提供connect功能。构造函数的签名如下 :

ZooKeeper(String connectionString, int sessionTimeout, Watcher watcher)

• connectionString - ZooKeeper集合主机。

• sessionTimeout - 会话超时（以毫秒为单位）。

• watcher - 实现“监视器”界面的对象。ZooKeeper集合通过监视器对象返回连接状态。

让我们创建一个新的帮助类 ZooKeeperConnection ，并添加一个方法 connect 。 connect 方法创建一个ZooKeeper对象，连接到ZooKeeper集合，然后返回对象。

这里 CountDownLatch 用于停止（等待）主进程，直到客户端与ZooKeeper集合连接。

ZooKeeper集合通过监视器回调来回复连接状态。一旦客户端与ZooKeeper集合连接，监视器回调就会被调用，并且监视器回调函数调用CountDownLatch的countDown方法来释放锁，在主进程中await。

以下是与ZooKeeper集合连接的完整代码。

编码：ZooKeeperConnection.java

// import java classes
import java.io.IOException;
import java.util.concurrent.CountDownLatch;

// import zookeeper classes
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.Watcher.Event.KeeperState;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.AsyncCallback.StatCallback;
import org.apache.zookeeper.KeeperException.Code;
import org.apache.zookeeper.data.Stat;

public class ZooKeeperConnection {

   // declare zookeeper instance to access ZooKeeper ensemble
   private ZooKeeper zoo;
   final CountDownLatch connectedSignal = new CountDownLatch(1);

   // Method to connect zookeeper ensemble.
   public ZooKeeper connect(String host) throws IOException,InterruptedException {
	
      zoo = new ZooKeeper(host,5000,new Watcher() {
		
         public void process(WatchedEvent we) {

            if (we.getState() == KeeperState.SyncConnected) {
               connectedSignal.countDown();
            }
         }
      });
		
      connectedSignal.await();
      return zoo;
   }

   // Method to disconnect from zookeeper server
   public void close() throws InterruptedException {
      zoo.close();
   }
}

保存上面的代码，它将在下一节中用于连接ZooKeeper集合。