EJB工作原理学习笔记!

EJB工作原理学习笔记

1 RMI工作原理
2 Websphere实现
3 weblogic实现
4 理解体会

1：RMI工作原理
首先说说RMI的工作原理，因为EJB毕竟是基于RMI的嘛。废话就不多讲了，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的例子代码网上可以找到不少，但绝大部分都是通过extend the interface Java.rmi.Remote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) {
this.age = age;
this.name = 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:

import java.io.ObjectOutputStream;
import java.io.ObjectInputStream;
import java.net.Socket;

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(socket.getOutputStream());
outStream.writeObject("age");
outStream.flush();

ObjectInputStream inStream =
new ObjectInputStream(socket.getInputStream());
return inStream.readInt();
}

public String getName() throws Throwable {
// pass method name to skeleton
ObjectOutputStream outStream =
new ObjectOutputStream(socket.getOutputStream());
outStream.writeObject("name");
outStream.flush();

ObjectInputStream inStream =
new ObjectInputStream(socket.getInputStream());
return (String)inStream.readObject();
}
}

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. Skeleton实现
代码:

import java.io.ObjectOutputStream;
import java.io.ObjectInputStream;
import java.net.Socket;
import java.net.ServerSocket;

public class Person_Skeleton extends Thread {
PersonServer myServer;

public Person_Skeleton(PersonServer server) {
// get reference of object server
this.myServer = server;
}

public void run() {
try {
// new socket at port 9000
ServerSocket serverSocket = new ServerSocket(9000);
// accept stub's request
Socket socket = serverSocket.accept();

while (socket != null) {
// get stub's request
ObjectInputStream inStream =
new ObjectInputStream(socket.getInputStream());
String method = (String)inStream.readObject();

// check method name
if (method.equals("age")) {
// execute object server's business method
int age = myServer.getAge();
ObjectOutputStream outStream =
new ObjectOutputStream(socket.getOutputStream());

// return result to stub
outStream.writeInt(age);
outStream.flush();
}

if(method.equals("name")) {
// execute object server's business method
String name = myServer.getName();
ObjectOutputStream outStream =
new ObjectOutputStream(socket.getOutputStream());

// return result to stub
outStream.writeObject(name);
outStream.flush();
}
}
} catch(Throwable t) {
t.printStackTrace();
System.exit(0);
}
}

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