如何通过编程检查Zookeeper是否正在运行？

Question

我正在使用CuratorFramework（我还是个新手）来连接Zookeeper实例。我想导入配置，但在此之前，我想测试我的程序是否能够连接到Zookeeper。到目前为止，我有这样的想法：

public Boolean zookeeperRunning() {
    CuratorFramework curatorFramework = 
            CuratorFrameworkFactory.newClient(zookeeperConn, new RetryOneTime(1));
    curatorFramework.start();

    CuratorZookeeperClient zkClient = curatorFramework.getZookeeperClient();
    return zkClient.isConnected();
}

我已经在本地机器上启动了ZooKeeper，我检查了与zkCli的连接，客户端可以连接到它。zookeeperCon变量设置为“127.0.0.1:2181”（我也尝试了localhost:2181）。问题是，尽管zkServer正在运行，但上述方法始终返回false。很可能语法不正确，但我无法在网上找到解决方案。你能帮我解释一下为什么上面的代码找不到正在运行的zkServer吗？

Answer 1

你应该连接zookeeper服务器，然后检查它。例如：

import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.test.TestingServer;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

import java.io.IOException;
import java.util.concurrent.TimeUnit;

import static org.junit.Assert.assertTrue;

public class ZkClientTest {
    TestingServer zkServer;

    @Before
    public void startZookeeper() throws Exception {
        zkServer = new TestingServer(2181);
        zkServer.start();
    }

    @After
    public void stopZookeeper() throws IOException {
        zkServer.stop();
    }

    @Test
    public void should_connect_to_zookeeper_server_when_config_use_default_localhost_2181()
        throws InterruptedException {
        CuratorFramework client = ZkClient.getInstance().getClient();
        try {
            client.blockUntilConnected(3, TimeUnit.SECONDS);
            assertTrue(ZkClient.getInstance().getClient().getZookeeperClient().isConnected());
        } finally {
            ZkClient.getInstance().close();
        }
    }
}

Answer 2

在获得zkClient后，应首先连接zookeeper，如果成功，则检查isConnected状态。演示代码如下（请参阅此处）：

private static CuratorFramework buildConnection(String url) {
    CuratorFramework curatorFramework = CuratorFrameworkFactory.newClient(url, new ExponentialBackoffRetry(100, 6));

    // start connection
    curatorFramework.start();
    // wait 3 second to establish connect
    try {
        curatorFramework.blockUntilConnected(3, TimeUnit.SECONDS);
        if (curatorFramework.getZookeeperClient().isConnected()) {
            return curatorFramework.usingNamespace("");
        }
    } catch (InterruptedException ignored) {
        Thread.currentThread().interrupt();
    }

    // fail situation
    curatorFramework.close();
    throw new RuntimeException("failed to connect to zookeeper service : " + url);
}

Answer 3

您可以使用生成器创建已配置的客户端，并设置侦听器来监视zk实例的状态：

// start client
client = CuratorFrameworkFactory.builder()
    .connectString("localhost:2181")
    .retryPolicy(new ExponentialBackoffRetry(1000, 3))
    .namespace("heavenize")
    .build();

client.getConnectionStateListenable().addListener(new ConnectionStateListener() {      
  @Override
  public void stateChanged(CuratorFramework client, ConnectionState newState)
  {
    log.info("State changed to: "+newState);
  }
});
}