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(); } } }}
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