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Java網絡編程基礎(四) ServerSocket類使用發布者：本站     時間：2020-05-06 16:05:46

由于SSClient使用了流套接字，所以服務程序也要使用流套接字。

這就要創建一個ServerSocket對象，ServerSocket有幾個構造函數，最簡單的是ServerSocket(int port)，當使用ServerSocket(int port)創建一個ServerSocket對象，port參數傳遞端口號，這個端口就是服務器監聽連接請求的端口，如果在這時出現錯誤將拋出IOException異常對象，否則將創建ServerSocket對象并開始準備接收連接請求。

接下來服務程序進入無限循環之中，無限循環從調用ServerSocket的accept()方法開始，在調用開始后accept()方法將導致調用線程阻塞直到連接建立。在建立連接后accept()返回一個最近創建的Socket對象，該Socket對象綁定了客戶程序的IP地址或端口號。

由于存在單個服務程序與多個客戶程序通訊的可能，所以服務程序響應客戶程序不應該花很多時間，否則客戶程序在得到服務前有可能花很多時間來等待通訊的建立，然而服務程序和客戶程序的會話有可能是很長的（這與電話類似），因此為加快對客戶程序連接請求的響應，典型的方法是服務器主機運行一個后臺線程，這個后臺線程處理服務程序和客戶程序的通訊。

為了示范我們在上面談到的慨念并完成SSClient程序，下面我們創建一個SSServer程序，程序將創建一個ServerSocket對象來監聽端口10000的連接請求，如果成功服務程序將等待連接輸入，開始一個線程處理連接，并響應來自客戶程序的命令。下面就是這段程序的代碼：

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