ZooKeeper api应用

一、环境搭建

1）创建一个maven工程

2）添加依赖

    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-core</artifactId>
            <version>2.8.2</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.apache.zookeeper/zookeeper -->
        <dependency>
            <groupId>org.apache.zookeeper</groupId>
            <artifactId>zookeeper</artifactId>
            <version>3.4.10</version>
        </dependency>
    </dependencies>

3）创建log4j.properties

log4j.rootLogger=INFO, stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d %p [%c] - %m%n
log4j.appender.logfile=org.apache.log4j.FileAppender
log4j.appender.logfile.File=target/spring.log
log4j.appender.logfile.layout=org.apache.log4j.PatternLayout
log4j.appender.logfile.layout.ConversionPattern=%d %p [%c] - %m%n

二、API使用

2.1、创建ZooKeeper客户端

package com.dianchou.zookeeper;

import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;
import org.junit.Before;

public class ZooKeeperTest {

    private static String connectString = "hadoop102:2181,hadoop103:2181,hadoop104:2181";
    private static int sessionTimeout = 2000;
    private ZooKeeper zkClient = null;

    @Before
    public void init() throws Exception {
        zkClient = new ZooKeeper(connectString, sessionTimeout, new Watcher() {
            @Override
            public void process(WatchedEvent event) {

                // 收到事件通知后的回调函数（用户的业务逻辑）
                System.out.println(event.getType() + "--" + event.getPath());

                // 再次启动监听
                try {
                    zkClient.getChildren("/", true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }
}

2.2、创建子节点

   /**
     * 创建子节点
     */
    @Test
    public void create() throws Exception {

        // 参数1：要创建的节点的路径； 参数2：节点数据 ； 参数3：节点权限 ；参数4：节点的类型
        String nodeCreated = zkClient.create("/atguigu", "jinlian".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
    }

2.3、获取子节点并监听节点变化

    /**
     * 获取子节点
     */
    @Test
    public void getChildren() throws Exception {

        List<String> children = zkClient.getChildren("/", true);

        for (String child : children) {
            System.out.println(child);
        }

        // 延时阻塞
        //Thread.sleep(Long.MAX_VALUE);
    }

2.4、判断Znode是否存在

    /**
     * 判断znode是否存在
     */
    @Test
    public void exist() throws Exception {

        Stat stat = zkClient.exists("/eclipse", false);
        System.out.println(stat == null ? "not exist" : "exist");
    }

三、监听服务器节点动态上下线案例

1）需求

某分布式系统中，主节点可以有多台，可以动态上下线，任意一台客户端都能实时感知到主节点服务器的上下线。

2）需求分析

3）具体实现

（1）先在集群上创建/servers节点

[zk: localhost:2181(CONNECTED) 10] create /servers "servers"
Created /servers

（2）服务器端向Zookeeper注册代码

package com.dianchou.zookeeper;

import org.apache.zookeeper.*;

import java.io.IOException;

public class DistributeServer {

    private static String connectString = "hadoop102:2181,hadoop103:2181,hadoop104:2181";
    private static int sessionTimeout = 2000;
    private ZooKeeper zk = null;
    private String parentNode = "/servers";

    // 创建到zk的客户端连接
    public void getConnect() throws IOException {

        zk = new ZooKeeper(connectString, sessionTimeout, new Watcher() {

            @Override
            public void process(WatchedEvent event) {

            }
        });
    }

    // 注册服务器
    public void registServer(String hostname) throws Exception{
        String create = zk.create(parentNode + "/server", hostname.getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
        System.out.println(hostname +" is online "+ create);
    }

    // 业务功能
    public void business(String hostname) throws Exception{
        System.out.println(hostname+" is working ...");
        Thread.sleep(Long.MAX_VALUE);
    }

    public static void main(String[] args) throws Exception {

        // 1获取zk连接
        DistributeServer server = new DistributeServer();
        server.getConnect();

        // 2 利用zk连接注册服务器信息
        server.registServer(args[0]);

        // 3 启动业务功能
        server.business(args[0]);
    }
}

（3）客户端代码

package com.dianchou.zookeeper;

import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;

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

public class DistributeClient {

    private static String connectString = "hadoop102:2181,hadoop103:2181,hadoop104:2181";
    private static int sessionTimeout = 2000;
    private ZooKeeper zk = null;
    private String parentNode = "/servers";

    // 创建到zk的客户端连接
    public void getConnect() throws IOException {
        zk = new ZooKeeper(connectString, sessionTimeout, new Watcher() {

            @Override
            public void process(WatchedEvent event) {

                // 再次启动监听
                try {
                    getServerList();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    // 获取服务器列表信息
    public void getServerList() throws Exception {

        // 1获取服务器子节点信息，并且对父节点进行监听
        List<String> children = zk.getChildren(parentNode, true);

        // 2存储服务器信息列表
        ArrayList<String> servers = new ArrayList<>();

        // 3遍历所有节点，获取节点中的主机名称信息
        for (String child : children) {
            byte[] data = zk.getData(parentNode + "/" + child, false, null);
            servers.add(new String(data));
        }

        // 4打印服务器列表信息
        System.out.println(servers);
    }

    // 业务功能
    public void business() throws Exception{

        System.out.println("client is working ...");
        Thread.sleep(Long.MAX_VALUE);
    }

    public static void main(String[] args) throws Exception {

        // 1获取zk连接
        DistributeClient client = new DistributeClient();
        client.getConnect();

        // 2获取servers的子节点信息，从中获取服务器信息列表
        client.getServerList();

        // 3业务进程启动
        client.business();
    }
}