// Server.java

import java.io.*;

import java.net.*;

public class Server extends Thread

{

public final static int Default_Port=6543;

protectd int port;

protectd ServerSockt listen_socket;

// 定義出錯例程：如果出現異常錯誤，退出程序。

Public static void fail(Exception e, String msg)

{

System.err.println(msg + ": " + e);

System.exit(1);

}

// 定義并啟動服務器的Socket 例程，監聽客戶機的連接請求。

public Server(int port)

{

if(port == 0) port = Default_Port;

this.port = port;

try

{

listen_socket = new ServerSocket(port);

}

catch(IOException e) fail(e, "Exception creating server socket");

System.out.println("Server: listening on port" + port);

This.start();

}

/* 下面為服務器監聽線程的主程序。該線程一直循環執行，監聽并接受客戶機發出的連接

請求。對每一個連接，均產生一個連接對象與之對應，通過Socket 通道進行通信。*/

public void run()

{

try

{

while(true)

{

Socket client_socket = listen_socket.accept();

Connection c = new Connection(client_socket);

}

}

catch(IOException e) fail(e,"Exception while listening for connections")

}

// 啟動服務器主程序

public static void main(String args[])

{

int port = 0;

if (args.length == 1)

{

try port = Integer.parseInt(args[0]);

catch(NumberFormatException e) port = 0;

}

new Server(port);

} // End of the main

} // End of Server class

//以下定義了Connection 類，它是用來處理與客戶機的所有通信的線程。

class Connection extends Thread

{

protected Socket client;

protected DataInputStream in;

protected PrintStream out;

// 初始化通信流并啟動線程

public Connection(Socket client_socket)

{

client = client_socket;

try

{

in = new DataInputStream(client.getinputStream());

out = new PrintStream(client.getOutputStream());

}

catch(IOException e)

{

try client.close();

catch(IOException e2);

System.err.println("Exception while getting socket streram: " + e);

Return;

}

this.start;

} // End of Connection method

// 服務例程：讀出一行文本；反轉文本；返回文本。

public void run()

{

String line;

StringBuffer revline;

int len;

try

{

for(;;)

{

// Read a line

line = in.readline();

if(line == null) break;

// Reverse the line

len = line.length();

revline = new StringBuffer(len);

for(int i = len-1; i >=0; i--)

revline.insert(len-1-I;line.charAt(i));

// Write out the reverse line

out.println(revline);

}

catch(IOException e);

finally try client.close();

catch(IOException e2);

}

// End of run method

}

// End of Connection class

3、編寫客戶機類Java 程序

// Client.java

import java.io.*;

import java.net.*;

public class Client extends

{

public static final int Default_Port = 6543;

// 定義出錯例程

public static final void usage()

{

System.out.println("Usage: Java Client []");

System.exit(0);

}

public static void main(String args[])

{

int port = Default_Port;

Socket s = null;

// 解析端口參數

if ((args.length != 1)&&(args.length != 2 )) usage();

if (args.length == 1)

port = Default_Port;

else

{

try port = Integer.parseInt(args[1]);

catch(NumberFormaatException e) usage();

}

try{

// 產生一個Socket ，通過指定的端口與主機通信。

s = new Socket(args[0], port);

// 產生用于發出和接收的文本字符流

DataInputStream sin = new DataInputStream(s.getInputStream());

PrintStream sout = new DataInputStream(s.getInputStream());

// 從控制臺讀入字符流

DataInputStream in = new DataInputStream(System.in);

// 返回連接的地址和端口

ystem.out.println("Connected to"+s.getInetAddress()+":"+ s.getPort());

String line;

For(;;)

{

// 顯示提示符

System.out.print(" >");

System.out.flush();

// 讀入控制臺輸入的一行字符

line = in.readline();

if (line == null) break;

// 將接收的文本行送至服務器

sout.println(line);

// 從服務器接收一行字符

line = sin.readline();

// Check if connection is closed(i.e. for EOF)

if(line == null)

{

System.out.println("Connection closed by server.");

Break;

}

// 在控制臺上顯示接收的字符

System.out.println(line);

}

// End of for loop

}

/ End of try

catch(IOException e ) System.err.println(e);

// Always be sure to close the socket

finally

{

try if(s != null) s.close();

catch(IOException e2);

}

} // End of main

} // End of Client