有关SSL的原理和介绍在网上已经有不少，对于Java下使用keytool生成证书，配置SSL通信的教程也非常多。但如果我们不能够亲自动手做一个SSL Sever和SSL Client，可能就永远也不能深入地理解Java环境下，SSL的通信是如何实现的。对SSL中的各种概念的认识也可能会仅限于可以使用的程度。本文通过构造一个简单的SSL Server和SSL Client来讲解Java环境下SSL的通信原理。
首先我们先回顾一下常规的Java Socket编程。在Java下写一个Socket服务器和客户端的例子还是比较简单的。以下是服务端的代码：
Java代码
1.package org.bluedash.tryssl;
2.
3.import java.io.BufferedReader;
4.import java.io.IOException;
5.import java.io.InputStbreamReader;
6.import java.io.PrintWriter;
7.import java.net.ServerSocket;
8.import java.net.Socket;
9.
10.public class Server extends Thread {
11. private Socket socket;
12.
13. public Server(Socket socket) {
14. this.socket = socket;
15. }
16.
17. public void run() {
18. try {
19. BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
20. PrintWriter writer = new PrintWriter(socket.getOutputStream());
21.
22. String data = reader.readLine();
23. writer.println(data);
24. writer.close();
25. socket.close();
26. } catch (IOException e) {
27.
28. }
29. }
30.
31. public static void main(String[] args) throws Exception {
32. while (true) {
33. new Server((new ServerSocket(8080)).accept()).start();
34. }
35. }
36.}
package org.bluedash.tryssl;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
public class Server extends Thread {
private Socket socket;
public Server(Socket socket) {
this.socket = socket;
}
public void run() {
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
PrintWriter writer = new PrintWriter(socket.getOutputStream());
String data = reader.readLine();
writer.println(data);
writer.close();
socket.close();
} catch (IOException e) {
}
}
public static void main(String[] args) throws Exception {
while (true) {
new Server((new ServerSocket(8080)).accept()).start();
}
}
}
服务端很简单：侦听8080端口，并把客户端发来的字符串返回去。下面是客户端的代码：
Java代码
1.package org.bluedash.tryssl;
2.
3.import java.io.BufferedReader;
4.import java.io.InputStreamReader;
5.import java.io.PrintWriter;
6.import java.net.Socket;
7.
8.public class Client {
9.
10. public static void main(String[] args) throws Exception {
11.
12. Socket s = new Socket("localhost", 8080);
13.
14. PrintWriter writer = new PrintWriter(s.getOutputStream());
15. BufferedReader reader = new BufferedReader(new InputStreamReader(s.getInputStream()));
16. writer.println("hello");
17. writer.flush();
18. System.out.println(reader.readLine());
19. s.close();
20. }
21.
22.}
package org.bluedash.tryssl;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;
public class Client {
public static void main(String[] args) throws Exception {
Socket s = new Socket("localhost", 8080);
PrintWriter writer = new PrintWriter(s.getOutputStream());
BufferedReader reader = new BufferedReader(new InputStreamReader(s.getI