Zookeeper API 相关操作(1)

使用 zookeeper原生的 API

 
    
      junit
      junit
      RELEASE
    

    
    
      org.apache.logging.log4j
      log4j-core
      2.8.2
    

    
    
      org.apache.zookeeper
      zookeeper
      3.5.7
    

    
    
      com.fasterxml.jackson.core
      jackson-databind
      2.8.3
    

ZkClient.java

package com.hejjon.zk;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.hejjon.zk.bean.MyConfig;
import org.apache.zookeeper.*;
import org.apache.zookeeper.data.Stat;
import org.junit.Before;
import org.junit.Test;

import java.io.IOException;
import java.util.List;


public class ZkClient {

    private static final String ZK_CONNECSTING = "42.192.150.81:2181";

    private static final int SESSION_TIMEOUT = 20000;
    private ZooKeeper zkClient;

    @Before
    public void init() throws IOException {

        zkClient = new ZooKeeper(ZK_CONNECSTING, SESSION_TIMEOUT, new Watcher() {
            public void process(WatchedEvent watchedEvent) {
                System.out.println("--------------------------------------------");
                List children = null;
                try {
                    children = zkClient.getChildren("/", true);
                    if (children != null) {
                        for (String child : children) {
                            System.out.println(child);
                        }
                    }
                } catch (KeeperException | InterruptedException e) {
                    e.printStackTrace();
                }

                System.out.println("--------------------------------------------");
            }
        });
    }


    
    @Test
    public void create() throws KeeperException, InterruptedException {
        String node = zkClient.create("/weicx", "testdata".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
    }

    
    @Test
    public void getChildren() throws KeeperException, InterruptedException {
        List children = zkClient.getChildren("/", true);

        for (String child : children) {
            System.out.println(child);
        }
        Thread.sleep(Long.MAX_VALUE);
    }

    
    @Test
    public void setData() throws KeeperException, InterruptedException, JsonProcessingException {
        Stat stat = null;
        ObjectMapper objectMapper = new ObjectMapper();
        MyConfig myConfig = new MyConfig();
        myConfig.setKey("aaaaa");
        myConfig.setName("bbbbb");
        byte[] bytes = objectMapper.writeValueAsBytes(myConfig);
        stat = zkClient.setData("/myconfig", bytes, -1);
        System.out.println(">>>>>>>>>>>>>>>> stat version: " + stat.getVersion());
    }


}

ZkClient2.java 

package com.hejjon.zk;

import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.hejjon.zk.bean.MyConfig;
import org.apache.zookeeper.*;
import org.apache.zookeeper.data.Stat;
import org.junit.Before;
import org.junit.Test;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.IOException;


public class ZkClient2 {

    private static Logger logger = LoggerFactory.getLogger(ZkClient2.class);

    private static final String ZK_CONNECSTING = "42.192.150.81:2181";

    private static final int SESSION_TIMEOUT = 20000;
    private ZooKeeper zkClient;


    @Before
    public void testWatchData() throws IOException, KeeperException, InterruptedException {

        ObjectMapper objectMapper = new ObjectMapper();
        zkClient = new ZooKeeper(ZK_CONNECSTING, SESSION_TIMEOUT, new Watcher() {
            @Override
            public void process(WatchedEvent event) {
                if (event.getType() == Event.EventType.NodeDataChanged
                        && event.getPath() != null && event.getPath().equals("/myconfig")) {
                    logger.info("节点 {} 数据发生了变化", event.getPath());
                    // 获取数据，并使用this再次设置此监听器，实现重复监听节点值的修改
                    try {
                        byte[] data = zkClient.getData("/myconfig", this, null);
                        MyConfig newConfig = objectMapper.readValue(data, MyConfig.class);
                        logger.info("节点数据变化：{}", newConfig);
                    } catch (KeeperException | InterruptedException | IOException e) {
                        e.printStackTrace();
                    }
                }
            }
        });
        // 创建数据对象，并将其转成byte 数组格式
        MyConfig myConfig = new MyConfig();
        myConfig.setKey("anykey");
        myConfig.setName("anyName");
        byte[] bytes = objectMapper.writeValueAsBytes(myConfig);

        // 判断 /myconfig 节点是否存在，若存在则先删除节点
        Stat exists = zkClient.exists("/myconfig", true);
        if (exists != null) {
            logger.info("节点 /myconfig 已存在");
            zkClient.delete("/myconfig", -1);
        }
        String s = zkClient.create("/myconfig", bytes, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
    }

    @Test
    public void getData() throws InterruptedException, KeeperException {
        byte[] data = zkClient.getData("/myconfig", true, null);
        String str = new String(data);
        System.out.println(">>>>>>>>>>>>> 获取到/myconfig 节点的值: " + str);

        Thread.sleep(Long.MAX_VALUE);    // 起到延时作用
    }


}

监听节点数据变化操作：

1. 首先运行 ZkClient2.java  的getData 方法，首先获取到的是/myconfig 节点原始的值。注意getData方法中加入了延时，所以程序会一直阻塞着，等待节点数据被修改。

2. 再运行 ZkClient.java 中的 setData 方法，此方法给节点 /myconfig 重新设置值。

3. 观察ZkClient2.java 的控制台打印信息，每次运行 setData方法控制台都会打印节点数据被修改的信息。

监听原理：

注意看监听节点数据变化的那一部分代码。由于这个监听是一次性的，即一次设置监听只可以监听到一次节点数据的变化，再次修改节点数据是监听不到的。所以写成

byte[] data = zkClient.getData("/myconfig", this, null);

将之前设置的监听器 this对象重新设置进去，这样就实现了重复的监听！

Junit 单元测试补充说明：

 注意到 junit的 @Before 注解的作用，加上此注解，可以使运行 junit测试类的任何方法之前都会执行一次 @Before 注解标记的方法。