RMI的原理与java代码实现

RMI(Remote Method Invocation)是一种执行远程调用的Java API。RMI的目的是使在不同计算机上运行的对象(Object)之间的调用行为类似于本地调用。

在RMI机制中，服务器(Server)应实现一定的功能并将其注册到注册表(Registry)中，客户端(Client)应在注册表的命名空间(Naming space)中获取对象

当机器A上的代码想要调用驻留在机器B上的远程对象时，始终有两个中间对象实际处理通信：存根(stub object)和骨架(skeleton object)。

存根(stub)对象位于机器A中，必须：

构建一个信息块(information block)，该信息块包括

要使用的远程对象的标识符(identifier)，

描述要调用的方法的操作号(operation number)

骨架对象位于机器B中，其任务是

要解组(unmarshal)参数，

要在服务器上的真实对象上调用所需的方法，

要捕获服务器上调用的返回值或异常(exception)，

要将包含封送格式(marshalled form)的值的返回给客户机上的存根。

一台电脑调用不同电脑上的‘获取随机数方法’，并把获得的随机数加和。

Client中Getregistry() 使用给定的localhost、端口号(19999)在本地创建一个存根对象(stub object)作为注册表远程对象的代理

Server中用 createRegistry() 绑定相同的端口。用Rebind() 使用名称绑定自己。这样就可以在RMI注册表中注册远程对象。

HelloClient.java

import java.rmi.*;
import java.rmi.registry.*;
import java.net.InetAddress;

public class HelloClient {

    public static void main(String[] args) {
		int num1 = (int)(Math.random()*100);
		int result = 0;
        String text = "rmi work";
        HelloInterface rmi = null;

        try {
            Registry registry = LocateRegistry.getRegistry("192.168.128.21", 19999);
            rmi = (HelloInterface) registry.lookup("server"); 
            System.out.println("Connected to Server");
        } catch (Exception e) {
            e.printStackTrace();
        }
        try {
            InetAddress address = InetAddress.getLocalHost();
            rmi.sendAddress(address);
        } catch (Exception e) {
            System.out.println("ERROR: Could not create the registry.");
            e.printStackTrace();
        }
        if (rmi != null) {
            try {
                System.out.println(rmi.getMessage(text));
                result = rmi.sum(num1, rmi.getMessage(text));
				rmi.sendMessage(Integer.toString(num1));
                rmi.setSum(result);
				rmi.printSum();
				
            } catch (RemoteException e) {
                e.printStackTrace();
            }
            System.out.println("Finished");
        }
    }
}

HelloServer.java

import java.rmi.*;
import java.rmi.registry.*;
import java.rmi.server.*;
import java.net.InetAddress;

public class HelloServer implements HelloInterface {
    private int sum;
	@Override
    public int sum(int num1, int num2) throws RemoteException {
        return num1+num2;
    }
    @Override
    public String say() throws RemoteException {
        return "message";
    }
    @Override
    public void sendMessage(String s) throws RemoteException {
        System.out.println(s);
    }

    @Override
    public void sendAddress(InetAddress address) throws RemoteException {
        System.out.println(address);
    }

    @Override
    public int getMessage(String text) throws RemoteException {
        return sum;
    }
    @Override
    public void setSum(int result) throws RemoteException {
        sum = result;
    }
    @Override
    public void printSum() throws RemoteException {
        System.out.println("sum: " + Integer.toString(sum));
    }

    public static void main(String[] args) {
        int sum = 0;
        Registry reg = null;
        try {
            reg = LocateRegistry.createRegistry(19999);
            InetAddress address = InetAddress.getLocalHost();
            System.out.println("DCS Starter:" + address);
        } catch (Exception e) {
            System.out.println("ERROR: Could not create the registry.");
            e.printStackTrace();
        }

        HelloServer serverObject = new HelloServer();
        try {
            reg.rebind("server", (HelloInterface) UnicastRemoteObject.exportObject(serverObject, 0));
        } catch (Exception e) {
            System.out.println("ERROR: Failed to register the server object.");
            e.printStackTrace();
        }
    }
}

HelloInterface.java

import java.rmi.*;
import java.net.InetAddress;

public interface HelloInterface extends Remote {
	public String say() throws RemoteException;
	public void sendMessage(String text) throws RemoteException;
	public void setSum(int result) throws RemoteException;
	public int getMessage(String text) throws RemoteException;
	public int sum(int num1, int num2) throws RemoteException;
	public void sendAddress(InetAddress address) throws RemoteException;
	public void printSum() throws RemoteException;
	}