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();      }  }