摘要：應(yīng)用場(chǎng)景回顧下應(yīng)用場(chǎng)景數(shù)據(jù)發(fā)布與訂閱服務(wù)注冊(cè)與發(fā)現(xiàn)分布式鎖分布式隊(duì)列選舉配置中心命名服務(wù)負(fù)載均衡實(shí)現(xiàn)服務(wù)注冊(cè)與發(fā)現(xiàn)服務(wù)注冊(cè)與發(fā)現(xiàn)再來(lái)看看在服務(wù)注冊(cè)與發(fā)現(xiàn)中的應(yīng)用代碼實(shí)現(xiàn)邏輯服務(wù)注冊(cè)創(chuàng)建的臨時(shí)的有序節(jié)點(diǎn)臨時(shí)的話斷開(kāi)連接了可以監(jiān)聽(tīng)到有序節(jié)點(diǎn)創(chuàng)

回顧下zk應(yīng)用場(chǎng)景：

數(shù)據(jù)發(fā)布與訂閱

服務(wù)注冊(cè)與發(fā)現(xiàn)

分布式鎖

分布式隊(duì)列

master選舉

配置中心

命名服務(wù)

負(fù)載均衡

服務(wù)注冊(cè)與發(fā)現(xiàn)

再來(lái)看看zk在服務(wù)注冊(cè)與發(fā)現(xiàn)中的應(yīng)用：

代碼實(shí)現(xiàn)邏輯：

服務(wù)注冊(cè)：

public class ServiceRegister {

    private  static final String BASE_SERVICES = "/services";
    private static final String  SERVICE_NAME="/products";

    public static  void register(String address,int port) {
        try {
            ZooKeeper zooKeeper = new ZooKeeper("localhost:2181",5000,(watchedEvent)->{});
            Stat exists = zooKeeper.exists(BASE_SERVICES + SERVICE_NAME, false);
            if(exists==null) {
                zooKeeper.create(BASE_SERVICES + SERVICE_NAME,"".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
            }
            String server_path = address+":"+port;
            //創(chuàng)建的臨時(shí)的有序節(jié)點(diǎn)
            //臨時(shí)的話斷開(kāi)連接了可以監(jiān)聽(tīng)到,有序節(jié)點(diǎn)創(chuàng)建代表每一個(gè)節(jié)點(diǎn)否則相同節(jié)點(diǎn)名稱無(wú)法創(chuàng)建
            zooKeeper.create(BASE_SERVICES + SERVICE_NAME+"/child",server_path.getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE,CreateMode.EPHEMERAL_SEQUENTIAL);
            System.out.println("產(chǎn)品服務(wù)注冊(cè)成功");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

發(fā)現(xiàn)服務(wù)：

    public class InitListener implements ServletContextListener {

    private  static final String BASE_SERVICES = "/services";
    private static final String  SERVICE_NAME="/products";

    private ZooKeeper zooKeeper;

    @Override
    public void contextInitialized(ServletContextEvent sce) {
        try {
             zooKeeper = new ZooKeeper("localhost:2181",5000,(watchedEvent)->{
                if(watchedEvent.getType() == Watcher.Event.EventType.NodeChildrenChanged  && watchedEvent.getPath().equals(BASE_SERVICES+SERVICE_NAME)) {
                    updateServiceList();
                }
            });

            updateServiceList();
        } catch (Exception e) {
            e.printStackTrace();
        }

    }

    private void updateServiceList() {
       try{
           List children = zooKeeper.getChildren(BASE_SERVICES  + SERVICE_NAME, true);
           List newServerList = new ArrayList();
           for(String subNode:children) {
               byte[] data = zooKeeper.getData(BASE_SERVICES  + SERVICE_NAME + "/" + subNode, false, null);
               String host = new String(data, "utf-8");
               System.out.println("host:"+host);
               newServerList.add(host);
           }
           //保存注冊(cè)服務(wù)的ip端口信息，以供遠(yuǎn)程rpc調(diào)用
           LoadBalance.SERVICE_LIST = newServerList;
       }catch (Exception e) {
           e.printStackTrace();
       }
    } 
}

public abstract class LoadBalance {
    public volatile static List SERVICE_LIST;

    public abstract String choseServiceHost();

}

/**
 * 隨機(jī)負(fù)載均衡算法
 */
public class RamdomLoadBalance extends LoadBalance {
    @Override
    public String choseServiceHost() {
        String result = "";
        if(!CollectionUtils.isEmpty(SERVICE_LIST)) {
            int index = new Random().nextInt(SERVICE_LIST.size());
            result = SERVICE_LIST.get(index);
        }
        return result ;
    }
}

再講講幾個(gè)關(guān)鍵點(diǎn)
1.注冊(cè)服務(wù)的時(shí)候需要?jiǎng)?chuàng)建臨時(shí)節(jié)點(diǎn),斷開(kāi)連接的時(shí)候也就是服務(wù)端掛了后節(jié)點(diǎn)刪除可監(jiān)聽(tīng)到
2.注冊(cè)服務(wù)的時(shí)候創(chuàng)建的是有序節(jié)點(diǎn),一般來(lái)說(shuō)相同服務(wù)都是有幾臺(tái)機(jī)器的,創(chuàng)建順序節(jié)點(diǎn)可區(qū)分多臺(tái)機(jī)器的服務(wù)
3.發(fā)現(xiàn)服務(wù)的一端監(jiān)聽(tīng)服務(wù)節(jié)點(diǎn)的子節(jié)點(diǎn)，有子節(jié)點(diǎn)被刪除了或者有新子節(jié)點(diǎn)創(chuàng)建即重新發(fā)現(xiàn)服務(wù)可用的機(jī)器

dubbo中基于zk的服務(wù)注冊(cè)與發(fā)現(xiàn)也是這個(gè)原理