Java RMI 入门案例

Java Remote Method Invocation(Java RMI) 是一个 Java API, 执行远程方法的调用，相当于 Remote Procedure Calls(RPC)。Java RMI 支持直接传输序列化的 Java 类，以及分布式的垃圾回收。

案例概况

实现一个简单的 Java RMI 可通过以下四步骤：

1. 启动 rmiregistry

2. 定义服务接口，实现服务接口，通过 rmic 工具创建存根文件( stub )

3. 实现服务端功能，并启动

4. 实现客户端功能，并调用服务端服务

具体实现

1. 启动 rmiregistry

grs:~ grs$ rmiregistry 

2. 定义服务接口，实现服务接口，通过 rmic 工具创建存根文件( stub )

 定义服务接口：

package service;

import java.rmi.Remote;
import java.rmi.RemoteException;

public interface GreetService extends Remote {

    String sayHello(String name) throws RemoteException;
    
}

实现服务接口：

package service;

import java.rmi.RemoteException;
import java.rmi.server.UnicastRemoteObject;

public class GreetServiceImpl extends UnicastRemoteObject implements GreetService {

    static final long serialVersionUID = 1L;

    public GreetServiceImpl() throws RemoteException {
        super();
    }

    @Override
    public String sayHello(String name) throws RemoteException {
        return "Hello - " + name;
    }
}

根据编译后的 GreetServiceImpl，使用 rmic 生成存根文件

grs:bin grs$ rmic service.GreetServiceImpl

执行后，目录如下

grs:bin grs$ tree
.
└── service
    ├── GreetService.class
    ├── GreetServiceImpl.class
    └── GreetServiceImpl_Stub.class

3 directories, 5 files
grs:bin grs$ 

3. 实现服务端功能，并启动

package server;

import java.net.MalformedURLException;
import java.rmi.AlreadyBoundException;
import java.rmi.Naming;
import java.rmi.RemoteException;
import java.rmi.registry.LocateRegistry;

import service.GreetServiceImpl;

public class Server {

    public static void main(String[] args){
        
        try {
            LocateRegistry.createRegistry(1098);
            Naming.bind("rmi://127.0.0.1:1098/GreetService", new GreetServiceImpl());

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

编译后，服务端文件目录结构如下：

grs:bin grs$ tree
.
├── server
│   └── Server.class
└── service
    ├── GreetService.class
    └── GreetServiceImpl.class

2 directories, 3 files
grs:bin grs$ 

启动服务端

grs:bin grs$ java -server server.Server

4. 实现客户端功能，并调用服务端服务

package client;

import java.net.MalformedURLException;
import java.rmi.Naming;
import java.rmi.NotBoundException;
import java.rmi.RemoteException;

import service.GreetService;

public class Client {

    public static void main(String[] args){
        
        try {
            String name = "rmi://127.0.0.1:1098/GreetService";
            GreetService greetService = (GreetService) Naming.lookup(name);
            
            System.out.println(greetService.sayHello(" Thhhhhhh "));
            
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (RemoteException e) {
            e.printStackTrace();
        } catch (NotBoundException e) {
            e.printStackTrace();
        }
    }
}

编译后文件目录结构如下

grs:bin grs$ tree
.
├── client
│   └── Client.class
└── service
    ├── GreetService.class
    └── GreetServiceImpl_Stub.class

2 directories, 3 files
grs:bin grs$ 

客户端调用远程端方法

grs:bin grs$ java -client client.Client
Hello -  Thhhhhhh 
grs:bin grs$ 

参考资料：

RMI 入门教程, DRY, 博客园

Introduction to Java RMI

[chapter 18] Distributed Computing : remote deployment with RMI, Head First Java

RMI, The Java Tutorials, Oracle

Java Remote Method Invocation, wikipedia