zookeeper应用场景

回顾下zk应用场景：

  1. 数据发布与订阅
  2. 服务注册与发现
  3. 分布式锁
  4. 分布式队列
  5. master选举
  6. 配置中心
  7. 命名服务
  8. 负载均衡

zookeeper实现服务注册与发现

服务注册与发现

再来看看zk在服务注册与发现中的应用：

代码实现逻辑：

服务注册：

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;            //创建的临时的有序节点            //临时的话断开连接了可以监听到,有序节点创建代表每一个节点否则相同节点名称无法创建            zooKeeper.create(BASE_SERVICES + SERVICE_NAME+"/child",server_path.getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE,CreateMode.EPHEMERAL_SEQUENTIAL);            System.out.println("产品服务注册成功");        } catch (Exception e) {            e.printStackTrace();        }    }}

发现服务：

    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<String> children = zooKeeper.getChildren(BASE_SERVICES  + SERVICE_NAME, true);           List<String> newServerList = new ArrayList<String>();           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);           }           //保存注册服务的ip端口信息，以供远程rpc调用           LoadBalance.SERVICE_LIST = newServerList;       }catch (Exception e) {           e.printStackTrace();       }    } }public abstract class LoadBalance {    public volatile static List<String> SERVICE_LIST;    public abstract String choseServiceHost();}/** * 随机负载均衡算法 */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 ;    }}

再讲讲几个关键点
1.注册服务的时候需要创建临时节点,断开连接的时候也就是服务端挂了后节点删除可监听到
2.注册服务的时候创建的是有序节点,一般来说相同服务都是有几台机器的,创建顺序节点可区分多台机器的服务
3.发现服务的一端监听服务节点的子节点，有子节点被删除了或者有新子节点创建即重新发现服务可用的机器

dubbo中基于zk的服务注册与发现也是这个原理