Java网络编程基础(四)ServerSocket类使用

由于SSClient使用了流套接字，所以服务程序也要使用流套接字。

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这就要创建一个ServerSocket对象，ServerSocket有几个构造函数，最简单的是ServerSocket(int port)，当使用ServerSocket(int port)创建一个ServerSocket对象，port参数传递端口号，这个端口就是服务器监听连接请求的端口，如果在这时出现错误将抛出IOException异常对象，否则将创建ServerSocket对象并开始准备接收连接请求。

接下来服务程序进入无限循环之中，无限循环从调用ServerSocket的accept()方法开始，在调用开始后accept()方法将导致调用线程阻塞直到连接建立。在建立连接后accept()返回一个最近创建的Socket对象，该Socket对象绑定了客户程序的IP地址或端口号。

由于存在单个服务程序与多个客户程序通讯的可能，所以服务程序响应客户程序不应该花很多时间，否则客户程序在得到服务前有可能花很多时间来等待通讯的建立，然而服务程序和客户程序的会话有可能是很长的（这与电话类似），因此为加快对客户程序连接请求的响应，典型的方法是服务器主机运行一个后台线程，这个后台线程处理服务程序和客户程序的通讯。

为了示范我们在上面谈到的慨念并完成SSClient程序，下面我们创建一个SSServer程序，程序将创建一个ServerSocket对象来监听端口10000的连接请求，如果成功服务程序将等待连接输入，开始一个线程处理连接，并响应来自客户程序的命令。下面就是这段程序的代码：

Listing 3: SSServer.java

// SSServer.java

import java.io.*;
import java.net.*;
import java.util.*;

class SSServer
{
public static void main (String [] args) throws IOException
{
System.out.println ("Server starting...\n");

// Create a server socket that listens for incoming connection
// requests on port 10000.

ServerSocket server = new ServerSocket (10000);

while (true)
{
// Listen for incoming connection requests from client
// programs, establish a connection, and return a Socket
// object that redivsents this connection.

Socket s = server.accept ();

System.out.println ("Accepting Connection...\n");

// Start a thread to handle the connection.

new ServerThread (s).start ();
}
}
}

class ServerThread extends Thread
{
private Socket s;

ServerThread (Socket s)
{
this.s = s;
}

public void run ()
{
BufferedReader br = null;
PrintWriter pw = null;

try
{
// Create an input stream reader that chains to the socket's
// byte-oriented input stream. The input stream reader
// converts bytes read from the socket to characters. The
// conversion is based on the platform's default character
// set.

InputStreamReader isr;
isr = new InputStreamReader (s.getInputStream ());

// Create a buffered reader that chains to the input stream
// reader. The buffered reader supplies a convenient method
// for reading entire lines of text.

br = new BufferedReader (isr);

// Create a print writer that chains to the socket's byte-
// oriented output stream. The print writer creates an
// intermediate output stream writer that converts
// characters sent to the socket to bytes. The conversion
// is based on the platform's default character set.

pw = new PrintWriter (s.getOutputStream (), true);

// Create a calendar that makes it possible to obtain date
// and time information.

Calendar c = Calendar.getInstance ();

// Because the client program may send multiple commands, a
// loop is required. Keep looping until the client either
// explicitly requests termination by sending a command
// beginning with letters BYE or implicitly requests
// termination by closing its output stream.

do
{
// Obtain the client program's next command.

String cmd = br.readLine ();

// Exit if client program has closed its output stream.

if (cmd == null)
break;

// Convert command to uppercase, for ease of comparison.

cmd = cmd.toUpperCase ();

// If client program sends BYE command, terminate.

if (cmd.startsWith ("BYE"))
break;

// If client program sends DATE or TIME command, return
// current date/time to the client program.

if (cmd.startsWith ("DATE") || cmd.startsWith ("TIME"))
pw.println (c.getTime ().toString ());

// If client program sends DOM (Day Of Month) command,
// return current day of month to the client program.

if (cmd.startsWith ("DOM"))
pw.println ("" + c.get (Calendar.DAY_OF_MONTH));

// If client program sends DOW (Day Of Week) command

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