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();
}
}
}
}
来源：oschina
链接：https://my.oschina.net/u/567457/blog/394958