Zookeeper动态更新服务器地址

        利用Zookeeper可实现服务发现功能，通过在节点下面创建数据来动态的更新服务地址

当服务地址发生变化时，服务提供者更改子节点下面的数据来更改url,服务消费者Watcher检测节点的变化，就获取节点下面的数据并且更新服务器地址

当服务器中的一个节点宕机或者leader宕机，zookeeper会自动选取领导，然后提供服务，只要宕机的数量小于zookeeper 服务器数量的一半仍然能提供良好的服务



基于Zookeeper的服务注册与发现架构

简单实现代码：

<dependency>
<groupId>org.apache.zookeeper</groupId>
<artifactId>zookeeper</artifactId>
<version>3.4.7</version>
</dependency>
<dependency>
<groupId>com.github.sgroschupf</groupId>
<artifactId>zkclient</artifactId>
<version>0.1</version>
</dependency>

服务消费者代码

package com.zookeerper.find;

import java.util.ArrayList;
import java.util.List;

import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.Watcher.Event.EventType;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.data.Stat;

public class AppClient{
private String groupNode = "sgroup";
private ZooKeeper zk;
private Stat stat = new Stat();
private volatile List<String> serverList;
private String zookeeperServer = "127.0.0.1:2181,127.0.0.1:2182";

/**
* 连接zookeeper
*/
public void connectZookeeper() throws Exception {
zk = new ZooKeeper(zookeeperServer, 5000, new Watcher() {

public void process(WatchedEvent event) {
// 如果发生了"/sgroup"节点下的子节点变化事件, 更新server列表, 并重新注册监听
if (event.getType() == EventType.NodeChildrenChanged
&& ("/" + groupNode).equals(event.getPath())) {
try {
updateServerList();
} catch (Exception e) {
e.printStackTrace();
}
}
}
});
updateServerList();
}

/**
* 更新server列表
*/
private void updateServerList() throws Exception {
List<String> newServerList = new ArrayList<String>();

// 获取并监听groupNode的子节点变化
// watch参数为true, 表示监听子节点变化事件.
// 每次都需要重新注册监听, 因为一次注册, 只能监听一次事件, 如果还想继续保持监听, 必须重新注册
List<String> subList = zk.getChildren("/" + groupNode, true);
for (String subNode : subList) {
// 获取每个子节点下关联的server地址
byte[] data = zk.getData("/" + groupNode + "/" + subNode, false, stat);
newServerList.add(new String(data, "utf-8"));
}

// 替换server列表
serverList = newServerList;

System.out.println("server list updated: " + serverList);
}

/**
* client的工作逻辑写在这个方法中 此处不做任何处理, 只让client sleep
*/
public void handle() throws InterruptedException {
Thread.sleep(Long.MAX_VALUE);
}

public static void main(String[] args) throws Exception {
AppClient ac = new AppClient();
ac.connectZookeeper();

ac.handle();
}
}

服务提供者代码：
package com.zookeerper.find;

import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooDefs.Ids;
import org.apache.zookeeper.ZooKeeper;

public class AppServer {

private String groupNode = "sgroup";
private String subNode = "sub";

/**
* 连接zookeeper
* @param address server的地址
*/
public void connectZookeeper(String address) throws Exception {

ZooKeeper zk = new ZooKeeper("127.0.0.1:2181,127.0.0.1:2182,127.0.0.1:2182", 5000, new Watcher() {
public void process(WatchedEvent event) {
// 不做处理
}
});

// 在"/sgroup"下创建子节点
// 子节点的类型设置为EPHEMERAL_SEQUENTIAL, 表明这是一个临时节点, 且在子节点的名称后面加上一串数字后缀
// 将server的地址数据关联到新创建的子节点上

String createdPath = zk.create("/" + groupNode + "/" + subNode, address.getBytes("utf-8"),
Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
System.out.println("create: " + createdPath);
}

/**
* server的工作逻辑写在这个方法中
* 此处不做任何处理, 只让server sleep
*/
public void handle() throws InterruptedException {
Thread.sleep(Long.MAX_VALUE);
}

public static void main(String[] args) throws Exception {
AppServer as = new AppServer();
as.connectZookeeper("asdfs3:8080");

as.handle();
}
}