的存根和骨架的工作原理呢

一、RMI工作原理

RMI的本质就是实现在不同JVM之间的调用,它的实现方法就是在两个JVM中各开一个Stub和Skeleton，二者通过socket通信来实现参数和返回值的传递。

有关RMI的例子代码上可以找到不少，但绝大部分都是通过extend the interface mote实现，已经封装的很完善了，不免使人有雾里看花的感觉。下面的例子是我在《Enterprise JavaBeans》里看到的，虽然很粗糙，但很直观，利于很快了解它的工作原理。

1、定义一个Person的接口，其中有两个business method, getAge() 和getName()

代码：

public interface Person {

public int getAge() throws Throwable;

public String getName() throws Throwable;

}

2、Person的实现PersonServer类

代码：

public class PersonServer implements Person {

int age;

String name;

public PersonServer(String name, int age) {

e = age;

= name;

}

public int getAge() {

return age;

}

public String getName() {

return name;

}

}

3、好，我们现在要在Client机器上调用getAge()和getName()这两个business method，那么就得编写相应的Stub(Client端)和Skeleton(Server端)程序。这是Stub的实现：

代码：

//存根（stub）的实现

import jectOutputStream;

import jectInputStream;

import cket;

public class Person_Stub implements Person {

Socket socket;

public Person_Stub() throws Throwable {

// connect to skeleton

socket = new Socket(\"computer_name\", 9000);

}

public int getAge() throws Throwable {

// pass method name to skeleton

ObjectOutputStream outStream =

new ObjectOutputStream(tOutputStream());

iteObject(\"age\");

ush();

ObjectInputStream inStream =

new ObjectInputStream(tInputStream());

return adInt();

}

public String getName() throws Throwable {

// pass method name to skeleton

ObjectOutputStream outStream =

new ObjectOutputStream(tOutputStream());

iteObject(\"name\");

ush();

ObjectInputStream inStream =

new ObjectInputStream(tInputStream());

return (String)adObject();

}

}

注意，Person_Stub和PersonServer一样，都implements Person。它们都实现了getAge()和getName()两个business method，不同的是PersonServer是真的实现，Person_Stub是建立socket连接，并向Skeleton发请求，然后通过Skeleton调用PersonServer的方法，最后接收返回的结果。

4、骨架（Skeleton）的实现

代码：

一名俄罗斯观众打扮成小熊的形象在看台上观赛。当日 import jectOutputStream;

import jectInputStream;

import cket;

import rverSocket;

public class Person_Skeleton extends Thread {

PersonServer myServer;

public Person_Skeleton(PersonServer server) {

// get reference of object server

Server = server;

}

public void run() {

try {

// new socket at port 9000

ServerSocket serverSocket = new ServerSocket(9000);

// accept stub\'s request

Socket socket = cept();

while (socket != null) {

// get stub\'s request

ObjectInputStream inStream =

new ObjectInputStream(tInputStream());

String method = (String)adObject();

// check method name

if (uals(\"age\")) {

// execute object server\'s business method

int age = tAge();

ObjectOutputStream outStream =

new ObjectOutputStream(tOutputStream());

// return result to stub

iteInt(age);

ush();

}

if(uals(\"name\")) {

// execute object server\'s business method

String name = tName();

ObjectOutputStream outStream =

new ObjectOutputStream(tOutputStream());

// return result to stub

iteObject(name);

ush();

}

}

} catch(Throwable t) {

intStackTrace();

it(0);

}

}

public static void main(String args []) {

// new object server

PersonServer person = new PersonServer(\"Richard\", 34);

Person_Skeleton skel = new Person_Skeleton(person);

art();

}

}

Skeleton类extends from Thread，它长驻在后台运行，随时接收client发过来的request。并根据发送过来的key去调用相应的business method。

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