Java操作ZooKeeper对象

Java操作ZooKeeper对象

1.使用Eclipse工具创建一个maven工程，配置pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>com.sl</groupId>
  <artifactId>zookeeper</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <packaging>war</packaging>

  <name>zookeeper</name>
  <url>http://maven.apache.org</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>

  <dependencies>
    <!--zk-->
    <dependency>
      <groupId>org.apache.zookeeper</groupId>
      <artifactId>zookeeper</artifactId>
      <version>3.4.6</version>
    </dependency>
    <!--zkclient-->
    <dependency>
      <groupId>com.github.sgroschupf</groupId>
      <artifactId>zkclient</artifactId>
      <version>0.1</version>
    </dependency>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
  </dependencies>
</project>

2.Java操作ZooKeeper对象

import java.io.IOException;
import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooDefs.Ids;
import org.apache.zookeeper.ZooKeeper;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

public class ZooKeeperTest {
    /**会话超时时间，设置与系统默认时间一致*/
    private final int SESSION_TIMEOUT = 30000;
    //创建ZooKeeper实例
    ZooKeeper zk;
    Watcher watcher = new Watcher() {
        public void process(WatchedEvent event) {
            System.out.println(event.toString());
        }
    };

    //初始化ZooKeeper实例
    @Before
    public void before() throws IOException {
        zk = new ZooKeeper("192.168.0.200:2181", SESSION_TIMEOUT, watcher);
    }

    @After
    public void after() throws InterruptedException {
        zk.close();
    }

    @Test
    public void create() throws KeeperException, InterruptedException {
        //在创建节点的时候，需要提供节点的名称、数据、权限以及节点类型
        System.out.println("1.创建ZooKeeper节点(znode:zoo2,数据:myData2,权限:OPEN_ACL_UNSAFE,节点类型:Persistent)");
        zk.create("/zoo2", "myData2".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
    }

    @Test
    public void getData() throws KeeperException, InterruptedException {
        System.out.println("2.查看是否创建成功:");
        System.out.println(new String(zk.getData("/zoo2", false, null)));
    }

    @Test
    public void setData() throws KeeperException, InterruptedException {
        System.out.println("3.修改节点数据:");
        zk.setData("/zoo2", "xiugai1234".getBytes(), -1);
    }

    @Test
    public void getSetData() throws KeeperException, InterruptedException {
        System.out.println("4.查看是否修改成功:");
        System.out.println(new String(zk.getData("/zoo2", false, null)));
    }

    @Test
    public void delete() throws InterruptedException, KeeperException {
        System.out.println("5.删除节点");
        zk.delete("/zoo2", -1);
    }

    @Test
    public void getStat() throws KeeperException, InterruptedException {
        //使用 exists函数时，如果节点不存在将返回一个nul值
        System.out.println("6.查看节点是否被删除:");
        System.out.println("节点状态:["+zk.exists("/zoo2", false)+"]");
    }

}

3.代码优化

zk的优点之一，就是高可用性，上面的代码连接的是单台zk server，如果这台server挂了，自然代码就会出错，事实上zk的API考虑到了这一点，把连接代码改成下面这样：

//初始化ZooKeeper实例
@Before
public void before() throws IOException {
    zk = new ZooKeeper("192.168.0.200:2181,192.168.0.200:2182,192.168.0.200:2183", SESSION_TIMEOUT, watcher);
}

即：IP1:port1,IP2:port2,IP3:port3… 用这种方式连接集群就行了，只要有超过半数的zk server还活着，应用一般就没问题。但是也有一种极罕见的情况，比如这行代码执行时，刚初始化完成，正准备连接IP1时，因为网络故障IP1对应的server挂了，仍然会报错（此时，zk还来不及选出新leader），这个问题详见：http://segmentfault.com/q/1010000002506725/a-1020000002507402，参考该文的做法，改成：

import java.util.concurrent.TimeUnit;

//初始化ZooKeeper实例
@Before
public void before() throws IOException {
    zk = new ZooKeeper("192.168.0.200:2181,192.168.0.200:2182,192.168.0.200:2183", SESSION_TIMEOUT, watcher);
    if (!zk.getState().equals(ZooKeeper.States.CONNECTED)) {
        while (true) {
            if (zk.getState().equals(ZooKeeper.States.CONNECTED)) {
                break;
             }
            try {
                TimeUnit.SECONDS.sleep(5);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
     }
}

这样写代码有些冗长，可以使用开源的zkClient，官方地址: https://github.com/sgroschupf/zkclient，使用方法很简单：
pom.xml配置

<!--zkclient-->
<dependency>
    <groupId>com.github.sgroschupf</groupId>
    <artifactId>zkclient</artifactId>
    <version>0.1</version>
</dependency>   

使用：

@Test
public static void zkClientTest() {
    ZkClient zkClient = new ZkClient("192.168.0.200:2181,192.168.0.200:2182,192.168.0.200:2183");
    String node2 = "/app2";
    if (!zkClient.exists(node2)) {
        zkClient.createPersistent(node2, "hello zk");
    }
    System.out.println(zkClient.readData(node2));
    zkClient.delete(node2);
    System.out.println(zkClient.exists(node2));
}

本文参考:
http://blog.youkuaiyun.com/shatelang/article/details/7596007
http://blog.youkuaiyun.com/huwei2003/article/details/49101269