java连接zookeeper

API

ZooKeeper官方提供了Java API，可以通过Java代码来连接zookeeper服务进行操作。可以连接、创建节点、获取节点数据、监听节点变化等操作，具体有以下几个重要的类：

ZooKeeper：ZooKeeper类是Java API的核心类，用于与ZooKeeper服务器建立连接，并提供了一系列方法来操作ZooKeeper的节点。
Watcher：Watcher是ZooKeeper的一个回调接口，当节点发生变化时会调用相应的方法进行通知。
CreateMode：CreateMode枚举类定义了节点的类型，包括永久节点、临时节点、顺序节点和临时顺序节点。
Stat：Stat类表示节点的元数据信息，比如修改版本、数据长度、子节点数量等。

添加依赖

<dependency>
    <groupId>org.apache.zookeeper</groupId>
    <artifactId>zookeeper</artifactId>
    <version>3.7.2</version>
</dependency>

操作例子

java 复制代码

String host = "localhost:2181";
//建立连接
zooKeeper = new ZooKeeper(host, 2000, null);
String path = "/test";
Watcher watcher = new Watcher() {
  @Override
  public void process(WatchedEvent watchedEvent) {
    System.out.println("Node changed: " + watchedEvent.getPath());
    System.out.println(watchedEvent);
  }
};
//获取节点状态 如果不存在返回null
Stat stat = zooKeeper.exists(path, false);
if(null != stat){
	System.out.println(stat.getCzxid()+"-"+stat.getAversion());
}

//创建节点 包含版本、时间、数据长度等信息
zooKeeper.create(path,"123".getBytes(),ZooDefs.Ids.OPEN_ACL_UNSAFE,CreateMode.PERSISTENT);
//添加watcher
zooKeeper.addWatch(path, watcher, AddWatchMode.PERSISTENT);

//获取节点数据
byte[] data = zooKeeper.getData(path, false, null);
System.out.println(new String(data));

zooKeeper.create(path+"/1","child1".getBytes(),ZooDefs.Ids.OPEN_ACL_UNSAFE,CreateMode.PERSISTENT);
//获取子节点
List<String> children = zooKeeper.getChildren(path, false);
System.out.println("childs size:"+children.size());
//删除子节点
zooKeeper.delete(path+"/1",-1);
zooKeeper.close();

zkClient

zkClient封装了zookeeper的官方api，简化了一些繁琐的操作，并提供了一些额外的功能，提高了开发效.

添加依赖

<dependency>
    <groupId>com.101tec</groupId>
    <artifactId>zkclient</artifactId>
    <version>0.11</version>
</dependency>

zkclient对节点数据的操作进行了序列化，这里先准备一个string类型的序列化类。需要实现ZkSerializer接口

public class ZkStringSerializer implements ZkSerializer {
    @Override
    public byte[] serialize(Object o) throws ZkMarshallingError {
        return String.valueOf(o).getBytes();
    }

    @Override
    public Object deserialize(byte[] bytes) throws ZkMarshallingError {
        return new String(bytes);
    }
}

基本操作

java 复制代码

ZkClient zkClient = new ZkClient("localhost:2181");
//自定义序列化 否则报错
zkClient.setZkSerializer(new ZkStringSerializer());
String path = "/test";
//判断节点是否存在
boolean exist = zkClient.exists(path);
System.out.println(exist);
if(!exist){//创建节点
    zkClient.create(path,"123", CreateMode.PERSISTENT);
}
//读取节点数据
System.out.println((String) zkClient.readData(path));
zkClient.writeData(path,"456");//设置节点数据
System.out.println((String) zkClient.readData(path));
zkClient.delete(path);//删除节点

zkClient.close();

节点变化事件

java 复制代码

String path = "/test";
/**
 * 节点变化事件
 * 只监听节点增减，不监听数据变化事件
 */
zkClient.subscribeChildChanges(path, new IZkChildListener() {
    @Override
    public void handleChildChange(String parentPath, List<String> children) throws Exception {
        System.out.println("节点"+parentPath+"发生变化");
        System.out.println(children);
    }
});
//节点操作，观察handleChildChange接收到对应事件
Thread.sleep(2000);
zkClient.createPersistent(path);
Thread.sleep(2000);
zkClient.createPersistent(path+"/child1");
Thread.sleep(2000);
zkClient.writeData(path+"/child1","123");
Thread.sleep(2000);
zkClient.delete(path+"/child1");
Thread.sleep(2000);
zkClient.delete(path);
Thread.sleep(100000);

节点数据变化事件

java 复制代码

    String path = "/test";
    /**
     * 节点变化事件,只检测当前节点，感知不到其子节点
     * 节点被删除或节点数据变化
     */
    zkClient.subscribeDataChanges(path, new IZkDataListener() {
        @Override
        public void handleDataChange(String s, Object o) throws Exception {
            System.out.println("节点："+s+"数据变为:"+o);
        }

        @Override
        public void handleDataDeleted(String s) throws Exception {
            System.out.println("节点："+s+"删除");
        }
    });

    Thread.sleep(2000);
    zkClient.createPersistent(path);
    Thread.sleep(2000);
    zkClient.createPersistent(path+"/child1");
    Thread.sleep(2000);
    zkClient.delete(path+"/child1");
    Thread.sleep(2000);
    zkClient.writeData(path,"123");
    Thread.sleep(2000);
    zkClient.delete(path);
    Thread.sleep(100000);
}

Curator

curator是另一个java连接zookeeper类库。功能更加强大。提供了连接重试、分布式锁、选举、队列等多种实际场景的用例。这里先简单搞个使用例子。

添加依赖

<dependency>
    <groupId>org.apache.curator</groupId>
    <artifactId>curator-framework</artifactId>
    <version>5.1.0</version>
</dependency>

curator-framework是基础的依赖，一些特定的使用方式需要添加不同的依赖，有curator-recipes、curator-x-discovery、curator-x-async等。

基本操作

java 复制代码

//创建连接
CuratorFramework client = CuratorFrameworkFactory.newClient("localhost:2181", new ExponentialBackoffRetry(1000, 3));
client.start();
String path = "/test";
client.checkExists().forPath(path);//判断是否存在
client.create().forPath(path, "123".getBytes());//创建节点
byte[] data = client.getData().forPath(path);//获取数据
System.out.println(new String(data));
client.setData().forPath(path, "456".getBytes());//设置数据
client.delete().forPath(path);//删除节点

client.close();

节点监听

java 复制代码

CuratorFramework client = CuratorFrameworkFactory.newClient("localhost:2181", new ExponentialBackoffRetry(1000, 3));
client.start();
String path = "/test";
NodeCache  nodeCache = new NodeCache(client,path);
//添加监听
nodeCache.getListenable().addListener(new NodeCacheListener() {
    @Override
    public void nodeChanged() throws Exception {
        ChildData data = nodeCache.getCurrentData();
        if (data != null) {
            System.out.println("Node changed: " + data.getPath() + ", value: " + new String(data.getData()));
        } else {
            System.out.println("Node deleted: " + nodeCache.getPath());
        }
    }
});
nodeCache.start();
client.create().forPath(path);
client.setData().forPath(path, "123".getBytes());
client.delete().forPath(path);
client.close();

这里NodeCache被标识@Deprecated，也不知道被什么方式代替了，后面再研究。先简单使用。