基于zookeeper的远程方法调用(RMI)的实现

采用zookeeper的命令服务，采用不同的目录结构存储不同模块不同服务的rmi的url，使用key来对应不同的服务。同时采用zookeeper解决了单点问题。

当有两个相同的服务注册时，因为采用的是临时有序znode，也会注册成功，客户端在调用时，发现有多个不同url，则会随机调取一个使用。

当一个服务down时，zookeeper会通知客户端更新url缓存，从而去掉down服务的链接。加入时，也会同步客户端url数据。

原理图如下：

1).目录结构

2).zookeeper调用

3).分布式调用

实现代码如下：

1.定义测试服务接口与实现

public interface Service extends Remote,Serializable{

    public void service(String name);
    
}

public class ServiceImpl implements Service{

    @Override
    public void service(String name) {
        System.out.println(name);
    }

}

2.RMIServer

public class RMIServer {

    private static final Logger logger = LoggerFactory
            .getLogger(RMIServer.class);

    private static ZooKeeper zk;

    private boolean isRegistry = false;

    //同步锁
    private Lock _lock = new ReentrantLock();
    
    private static final Map<String,String> CACHED_URL = new HashMap<String,String>();

    public RMIServer() {
        zk = connectServer();
        new Thread(new Runnable() {
            @Override
            public void run() {
                while (true) {
                    try {
                        Thread.currentThread().sleep(3000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    logger.info("check zk...");
                    _lock.lock();
                    if (zk != null) {
                        if (zk.getState().isAlive()
                                && zk.getState().isConnected()) {
                            logger.info("zk is ok");
                            _lock.unlock();
                            continue;
                        }
                    }
                    close();
                    logger.info("reConnectServer ...");
                    zk = connectServer();
                    Iterator<String> it = CACHED_URL.keySet().iterator();
                    while(it.hasNext()){
                        String key = it.next();
                        String url = CACHED_URL.get(key);
                        createNode(zk,url,key);
                    }
                    logger.info("reConnectServer ok");
                    _lock.unlock();
                }

            }

            private void close() {
                if(zk!=null){
                    try {
                        zk.close();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    zk = null;
                }
            }
        }).start();
    }

    // 用于等待 SyncConnected 事件触发后继续执行当前线程
    private CountDownLatch latch = new CountDownLatch(1);

    // 发布 RMI 服务并注册 RMI 地址到 ZooKeeper 中
    public void publish(Remote remote, String key) {
        _lock.lock();
        String url = publishService(remote); // 发布 RMI 服务并返回 RMI 地址
        if (url != null) {
            if (zk != null) {
                if (zk.getState().isAlive() && zk.getState().isConnected()) {
                } else {
                    if(zk!=null){
                        try {
                            zk.close();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                        zk = null;
                    }
                    zk = connectServer();
                }
                createNode(zk, url, key); // 创建 ZNode 并将 RMI 地址放入 ZNode 上
            }
        }
        _lock.unlock();

    }

    // 发布 RMI 服务
    private String publishService(Remote remote) {
        String url = null;
        try {
            String host = ConfigHelp.getLocalConifg("rmiIP", "127.0.0.1");
            int port = Integer.valueOf(ConfigHelp.getLocalConifg("rmiPort",
                    "10990"));
            url = String.format("rmi://%s:%d/%s", host, port, remote.getClass()
                    .getName());
            if (!isRegistry) {
                LocateRegistry.createRegistry(port);
                isRegistry = true;
            }
            Naming.rebind(url, remote);
            logger.debug("publish rmi service (url: {})", url);
        } catch (RemoteException | MalformedURLException e) {
            logger.error("", e);
        }
        return url;
    }

    // 连接 ZooKeeper 服务器
    private ZooKeeper connectServer() {
        ZooKeeper zk = null;
        try {

            zk = new ZooKeeper(ConfigHelp.ZK_CONNECTION_STRING,
                    ConfigHelp.ZK_SESSION_TIMEOUT, new Watcher() {
                        @Override
                        public void process(WatchedEvent event) {
                            if (event.getState() == Event.KeeperState.SyncConnected) {
                                latch.countDown(); // 唤醒当前正在执行的线程
                            }
                        }
                    });
            latch.await(); // 使当前线程处于等待状态
        } catch (IOException | InterruptedException e) {
            logger.error("", e);
        }
        if (zk != null) {
            try {
                Stat stat = zk.exists(ConfigHelp.ZK_ROOT_PATH, false);
                if (stat == null) {
                    String path = zk.create(ConfigHelp.ZK_ROOT_PATH,
                            "".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE,
                            CreateMode.PERSISTENT); // 创建一个临时性且有序的 ZNode
                    logger.info("create zookeeper node ({})", path);
                }
                stat = zk.exists(ConfigHelp.ZK_RMI_PATH, false);
                if (stat == null) {

                    String path = zk.create(ConfigHelp.ZK_RMI_PATH,
                            "".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE,
                            CreateMode.PERSISTENT); // 创建一个临时性且有序的 ZNode
                    logger.info("create zookeeper node ({})", path);
                }
            } catch (KeeperException | InterruptedException e) {
                e.printStackTrace();
            }
        }
        return zk;
    }

    // 创建 ZNode
    private void createNode(ZooKeeper zk, String url, String key) {
        try {
            CACHED_URL.put(key, url);
            byte[] data = (key + "#:#" + url).getBytes();
            String path = zk.create(ConfigHelp.ZK_RMI_PATH + "/", data,
                    ZooDefs.Ids.OPEN_ACL_UNSAFE,
                    CreateMode.EPHEMERAL_SEQUENTIAL); // 创建一个临时性且有序的 ZNode
            logger.info("create zookeeper node ({} => {})", path, url);
        } catch (KeeperException | InterruptedException e) {
            logger.error("", e);
            e.printStackTrace();
        }
    }

    public static void main(String[] args) throws Exception {
        RMIServer server = new RMIServer();
        Service service = new ServiceImpl();
        server.publish(service, "Test");
        server.publish(service, "Test1");
        Thread.currentThread().sleep(50000);
        server.publish(service, "Test3");
        Thread.currentThread().sleep(Integer.MAX_VALUE);
    }
}

3.RMIClient

public class RMIClient {
    
 
    private static final Logger logger = LoggerFactory.getLogger(RMIClient.class);
 
    // 用于等待 SyncConnected 事件触发后继续执行当前线程
    private CountDownLatch latch = new CountDownLatch(1);
 
    // 定义一个 volatile 成员变量，用于保存最新的 RMI 地址（考虑到该变量或许会被其它线程所修改，一旦修改后，该变量的值会影响到所有线程）
    private volatile HashMap<String,List<String>> dataMap = new HashMap<String, List<String>>();
 
    private Lock _lock = new ReentrantLock();
    
    private static  ZooKeeper zk;
    
    // 构造器
    public RMIClient() {
        zk = connectServer(); // 连接 ZooKeeper 服务器并获取 ZooKeeper 对象
        watchNode();
        new Thread(new Runnable() {
            
            @Override
            public void run() {
                while (true) {
                    try {
                        Thread.currentThread().sleep(3000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    _lock.lock();
                    if (zk != null) {
                        if (zk.getState().isAlive()
                                && zk.getState().isConnected()) {
                            _lock.unlock();
                            continue;
                        }
                    }
                    if(zk!=null){
                        try {
                            zk.close();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                        zk = null;
                    }
                    zk = connectServer();
                    _lock.unlock();
                }
            }
        }).start();
    }
 
    // 查找 RMI 服务
    public <T extends Remote> T lookup(String key) {
        T service = null;
        int size = dataMap.size();
        if (size > 0) {
            String url = null;
            if(dataMap.containsKey(key)){
                List<String> urlList = dataMap.get(key);
                if(urlList.size()>0){
                    if(urlList.size()==1){
                         url = urlList.get(0);
                    }else{
                        url = urlList.get(ThreadLocalRandom.current().nextInt(size)); 
                    }
                }
                 service = lookupService(url,key); // 从 JNDI 中查找 RMI 服务
            }
        }
        return service;
    }
 
    // 连接 ZooKeeper 服务器
    private ZooKeeper connectServer() {
        ZooKeeper zk = null;
        try {
            zk = new ZooKeeper(ConfigHelp.ZK_CONNECTION_STRING, ConfigHelp.ZK_SESSION_TIMEOUT, new Watcher() {
                @Override
                public void process(WatchedEvent event) {
                    if (event.getState() == Event.KeeperState.SyncConnected) {
                        latch.countDown(); // 唤醒当前正在执行的线程
                    }
                }
            });
            latch.await(); // 使当前线程处于等待状态
        } catch (IOException | InterruptedException e) {
            logger.error("", e);
        }
        return zk;
    }
 
    // 观察 /registry 节点下所有子节点是否有变化
    private void watchNode() {
        _lock.lock();
        if(zk!=null&&zk.getState().isAlive()&&zk.getState().isConnected()){
            
        }else{
            if(zk!=null){
                try {
                    zk.close();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                zk = null;
            }
            zk = connectServer();
        }
        try {
            List<String> nodeList = zk.getChildren(ConfigHelp.ZK_RMI_PATH, new Watcher() {
                @Override
                public void process(WatchedEvent event) {
                    if (event.getType() == Event.EventType.NodeChildrenChanged) {
                        watchNode(); // 若子节点有变化，则重新调用该方法（为了获取最新子节点中的数据）
                    }
                }
            });
            List<String> dataList = new ArrayList<>(); // 用于存放 /registry 所有子节点中的数据
            HashMap<String,List<String>> dataMap = new HashMap<String, List<String>>();
            for (String node : nodeList) {
                byte[] data = zk.getData(ConfigHelp.ZK_RMI_PATH + "/" + node, false, null); // 获取 /registry 的子节点中的数据
                dataList.add(new String(data));
                String d = new String(data).toString();
                String key = d.split("#:#")[0];
                String url = d.split("#:#")[1];
                if(dataMap.containsKey(key)){
                    dataMap.get(key).add(url);
                }else{
                    List<String> list = new ArrayList<String>();
                    list.add(url);
                    dataMap.put(key, list);
                }
            }
            logger.debug("node data: {}", dataList);
            this.dataMap = dataMap;
        } catch (KeeperException | InterruptedException e) {
            logger.error("", e);
        }
        _lock.unlock();
    }
 
    // 在 JNDI 中查找 RMI 远程服务对象
    @SuppressWarnings("unchecked")
    private <T> T lookupService(String url,String key) {
        T remote = null;
        try {
            remote = (T) Naming.lookup(url);
        } catch (NotBoundException | MalformedURLException | RemoteException e) {
            if (e instanceof ConnectException) {
                // 若连接中断，则使用 urlList 中第一个 RMI 地址来查找（这是一种简单的重试方式，确保不会抛出异常）
                logger.error("ConnectException -> url: {}", url);
                if(dataMap.containsKey(key)){
                    List<String> urlList = dataMap.get(key);
                    if(urlList.size()>0){
                        return lookupService(urlList.get(0),key);
                    }
                }
            }
            logger.error("", e);
        }
        return remote;
    }
    public static void main(String[] args) {
        RMIClient client = new RMIClient();
        while(true){
            Service service = client.lookup("Test");
            service.service("test12");
            try {
                Thread.sleep(2000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

4.RMIHelper

public class RMIHelper {
    
    private static final RMIServer SERVER = new RMIServer();
    
    private static final RMIClient CLIENT = new RMIClient();
    
    public static synchronized void publish(Remote remote,String key){
        SERVER.publish(remote, key);
    }
    
    public static synchronized <T extends Remote> T lookup(String key){
        return CLIENT.lookup(key);
    }
    
    public static void main(String[] args) throws Exception {
        while(true){
            Service service = RMIHelper.lookup("Test");
            service.service("test12");
            Service service1 = RMIHelper.lookup("Test1");
            service1.service("test12");
            try {
                Thread.sleep(2000);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        
    }
}