RMI简单实例

1、定义一个表示远程服务的接口RemoteInterface，必须继承自java.rmi.Remote（Remote是一个标识，没有抽象的方法）。

在RemoteInterface里定义可被远程调用的方法，方法必须声明抛出java.rmi.RemoteException。

public interface RemoteInterface extends Remote {
	public long serverTime() throws RemoteException;
}

2、定义一个类RemoteClass继承自UnicastRemoteObject类，且实现了远程服务接口RemoteInterface，

public class RemoteClass extends UnicastRemoteObject implements RemoteInterface {
	private static final long serialVersionUID = 1L;

	protected RemoteClass() throws RemoteException {
		super();
	}

	@Override
	public long serverTime() throws RemoteException {
		return System.currentTimeMillis();
	}

	public static void main(String[] args) {
		try {
			RemoteClass rc = new RemoteClass();

			// 创建一个远程对象注册表，并绑定到端口8985；
			// 如果要绑定IP，则使用createRegistry(int port, RMIClientSocketFactory csf, RMIServerSocketFactory ssf)，通过
			// 在RMIClientSocketFactory、RMIServerSocketFactory的定制实现里绑定IP。
			Registry registry = LocateRegistry.createRegistry(8985);

			// 在rmi远程对象注册表注册一个远程对象。
			registry.bind("serverTime", rc);

		} catch (RemoteException e) {
			e.printStackTrace();
		} catch (AlreadyBoundException e) {
			e.printStackTrace();
		}

	}

}

3、客户端查找远程对象的示例

public class ClientClass {

	public static void main(String[] args) {
		// 通过远程注册表查找远程对象
		try {
			// 获取远程注册表
			Registry remoteRegistry = LocateRegistry.getRegistry("127.0.0.1", 8985);

			// 从远程注册表获取远程对象
			RemoteInterface remoteTime = (RemoteInterface)remoteRegistry.lookup("serverTime");

			for(int i = 0; i < 10; i++) {
				System.out.println("remote time :" + remoteTime.serverTime());
			}

		} catch (RemoteException e) {
			e.printStackTrace();
		} catch (NotBoundException e) {
			e.printStackTrace();
		}
		// 通过远程注册表查找远程对象 end


		System.out.println("================================================");

		// 通过rmi协议查找远程对象
		try {
			// 查找远程对象
			RemoteInterface remoteTime = (RemoteInterface)Naming.lookup("rmi://127.0.0.1:8985/serverTime");

			for(int i = 0; i < 10; i++) {
				System.out.println("remote time :" + remoteTime.serverTime());
			}

		} catch (MalformedURLException e) {
			e.printStackTrace();
		} catch (RemoteException e) {
			e.printStackTrace();
		} catch (NotBoundException e) {
			e.printStackTrace();
		}
	}

}

4、编译这些类，用rmic编译器生成根：

rmic RemoteClass

在对应的包下会出现一个文件：RemoteClass_Stub.class

5、先后运行 RemoteClass ，ClientClass ，结果大致如下：

remote time :1303288008309

remote time :1303288008309

remote time :1303288008309

remote time :1303288008309

remote time :1303288008309

remote time :1303288008309

remote time :1303288008309

remote time :1303288008309

remote time :1303288008309

remote time :1303288008309

================================================

remote time :1303288008325

remote time :1303288008325

remote time :1303288008325

remote time :1303288008325

remote time :1303288008325

remote time :1303288008325

remote time :1303288008325

remote time :1303288008325

remote time :1303288008325

remote time :1303288008325

执行远程方法调用成功。

网上找到的绑定IP的其他方法，未验证：

System.setProperty("java.rmi.server.hostname", ip);

Naming.rebind("rmi://"+serverPath + ":" + port + "/" + serverName,
serverInterface);