what that?

Zookeeper在分布式开发中使用频繁,但许多框架都对其进行了封装,初学者可能无法较好的理解其工作原理,该文章演示了使用Zookeeper实现服务注册,服务发现的简单demo,希望能达到抛砖引玉的效果;

why need RegisterCenter?

之所以需要访问注册和服务发现是因为分布式系统中,服务之间需要相互调用,但若每个服务自己维护一份依赖的服务信息的话,就显得很麻烦,且自身维护的数据无法保证其实时性,当依赖的服务信息发生变更时,无法及时获取更新,解决方案就是引入一个注册中心,服务提供方将自己的信息写入到注册中心,服务使用方从注册中心来获取服务信息; 如下图:

client表示服务使用方,server表示服务提供方

实现的效果: 客户端可自动发现服务信息,当服务状态发生变化时(上线,下线,更换地址),客户端可已及时响应变化,效果如下图:

效果演示

1|0实现

1.首先保证Zookeeper以安装启动,且可以正常访问

2.创建Maven项目并添加Zookeeper的Java客户端依赖(注意版本号需>3.6)

				<dependency><groupId>org.apache.zookeeper</groupId><artifactId>zookeeper</artifactId><version>3.6.1</version></dependency>

3.编写服务提供方

package com.jerry;import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.ZooDefs;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.data.ACL;import java.io.IOException;
import java.io.InputStream;
import java.net.*;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.Enumeration;import static java.net.InetAddress.getLocalHost;public class UserService {public static void main(String[] args) throws IOException, InterruptedException, KeeperException {new UserService().serving();}public void serving() throws IOException, KeeperException, InterruptedException {//获取本机ip地址String ip = null;Enumeration<NetworkInterface> networkInterfaces = NetworkInterface.getNetworkInterfaces();while (networkInterfaces.hasMoreElements()) {NetworkInterface ni = (NetworkInterface) networkInterfaces.nextElement();Enumeration<InetAddress> nias = ni.getInetAddresses();while (nias.hasMoreElements()) {InetAddress ia = (InetAddress) nias.nextElement();if (!ia.isLinkLocalAddress() && !ia.isLoopbackAddress() && ia instanceof Inet4Address) {ip = ia.getHostAddress();}}}int port = 8988;//启动服务ServerSocket socket = new ServerSocket(port);System.out.println("服务器已启动...");//注册服务serverRegister(ip, port);//处理请求clientHandler(socket);}private void clientHandler(ServerSocket socket) throws IOException {while (true) {Socket accept = socket.accept();InputStream inputStream = accept.getInputStream();byte[] barr = new byte[1024];while (true) {int size = inputStream.read(barr);if (size == -1) {//System.out.println("客户端已关闭..");accept.close();break;}String s = new String(barr, 0, size);//输出客户端消息System.out.println(accept.getInetAddress().getHostAddress() + ": " + s);}}}private void serverRegister(String ip, int port) throws IOException, KeeperException, InterruptedException {//注册服务ZooKeeper zooKeeper = new ZooKeeper("10.211.55.4", 2181, null);try {ArrayList<ACL> acl = new ArrayList<>();acl.add(new ACL(31, ZooDefs.Ids.ANYONE_ID_UNSAFE));zooKeeper.create("/userServer", (ip + ":" + port).getBytes(StandardCharsets.UTF_8), acl, CreateMode.EPHEMERAL);System.out.println("服务发布成功!");} catch (KeeperException | InterruptedException e) {e.printStackTrace();throw e;}}
}

4.编写服务服务使用方

package com.yyh;import org.apache.zookeeper.*;import java.io.IOException;
import java.io.OutputStream;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.util.Scanner;public class UserClient implements Watcher {String node = "/userServer"; //服务信息所在的节点 服务提供方和服务消费方一致private ZooKeeper zooKeeper;String server_ip;int server_port;public static void main(String[] args) throws Exception {//开始服务监听UserClient userClient = new UserClient();userClient.run();//当访问可用时与服务交互Scanner scanner = new Scanner(System.in);while (true){System.out.println("输入要发送的信息(e:退出)");String text = scanner.next();if (text.equals("e"))System.exit(-1);if (userClient.server_ip == null){System.err.println("没有可用的服务...");}else {userClient.sendToServer(text);}}}private void run() throws Exception {//连接zookeeperzooKeeper = new ZooKeeper("10.211.55.4:2181", 3000, null);//尝试获取服务信息getServerInfo();//添加对服务信息的永久监听zooKeeper.addWatch(node,this,AddWatchMode.PERSISTENT);}//获取服务信息private void getServerInfo()  {try {byte[] data = zooKeeper.getData(node, false, null);String[] infos = new String(data).split(":");server_ip = infos[0];server_port = Integer.parseInt(infos[1]);System.out.println("获取服务信息成功!");System.out.println(server_ip+":"+ server_port);} catch (KeeperException e) {System.err.println("服务信息不存在! 等待服务上线........");} catch (InterruptedException e) {e.printStackTrace();}}//当节点状态发送变化时将执行该方法(通知处理)@Overridepublic void process(WatchedEvent event) {if (event.getPath().equals(node)) {//根据具体逻辑处理不同的事件类型,此处只关心节点的创建删除和更新if (event.getType() == Event.EventType.NodeCreated) {System.err.println("服务上线了");getServerInfo();} else if (event.getType() == Event.EventType.NodeDataChanged) {System.err.println("服务更新了");getServerInfo();}else if (event.getType()== Event.EventType.NodeDeleted){server_ip = null;server_port = 0;System.err.println("服务下线了");}}}public void sendToServer(String text) {InetSocketAddress server_address = new InetSocketAddress(server_ip, server_port);Socket socket = new Socket();try {socket.connect(server_address);//System.out.println("连接服务器成功!");OutputStream outputStream = socket.getOutputStream();outputStream.write(text.getBytes());System.out.println("消息发送成功!");} catch (IOException e) {e.printStackTrace();}try {socket.close();} catch (IOException e) {e.printStackTrace();}}
}

5.打包服务端代码,该步骤可忽略,仅为了测试客户端正确性, 为了在打包时附带其全部依赖,此处借助Spring的打包插件,在pom中添加以下内容:

注意:Spring-boot打包插件会自动获取项目中的主函数,必须保证主函数只有一个,所以需要暂时注释客户端的主函数,最后执行maven的package,得到jar包

6.将jar上传至虚拟机并运行

java -jar ZookeeperTest-1.0-SNAPSHOT.jar

若没有其他问题则客户端依然可以正常连接服务器发送消息;

以上便是使用Zookeeper实现服务注册和服务发现的具体步骤,在实际开发中,我们可能还会将提供的服务部署为集群,这时可将集群中的各个服务信息作为子节点注册到指定节点下,客户端监听该节点变化,获取子节点列表从而获取到服务列表,还可以在此基础上加上负载均衡算法实现对服务列表的合理访问; 如图:

文章结束了，如果大家觉得有用，请大家多多关注哈，感谢大家的阅读！