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Java Gossip: HTTP 重定向

如果您的网站移站了，而您只是要作一个重定向的动作，则可以撰写一个可以丢出重定向标头的简单服务器，当浏览器接收到重定向标头时，会重定向您指定的网站。

HTTP 协定中，重定向标头是由Location: 控制，这个标头需浏览器支持HTTP/1.0以上才有作用，所以最好再指定一个备用的HTML网页，如果使用者的浏览器不支持HTTP/1.0以上，可以直接显示HTML网页告知讯息，例如：

moved.html

<html> 
<head> 
</head> 
<body> 
This site has been moved to: http://caterpillar.onlyfun.net 
</body> 
</html>

下面这个程序可以让浏览器重定向至指定的网址，您可以自行指定连接埠、重定向网页与重定向网址：

HttpRedirectServer.java

package onlyfun.caterpillar;

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

public class HttpRedirectServer {
    public static void main(String[] args) { 
        int port = Integer.parseInt(args[0]);
        String movedHtml = args[1];
        String redirectUrl = args[2];

        try { 
            System.out.println("HTTP 重定向..."); 
            ServerSocket serverSkt = new ServerSocket(port); 

            while(true) { 
                System.out.printf("倾听连线于 %d ...%n", port); 
                Socket clientSkt = serverSkt.accept(); 
                System.out.printf("%s 连线....", 
                        clientSkt.getInetAddress().toString()); 

                PrintStream printStream = 
                    new PrintStream(clientSkt.getOutputStream()); 

                BufferedReader protocolReader = 
                    new BufferedReader(
                            new InputStreamReader( 
                                    clientSkt.getInputStream())); 

                String readin = protocolReader.readLine(); 
                String[] tokens = readin.split("[ \t]"); 


                // 是否支持HTTP/1.0以上
                if(tokens.length >= 3 && tokens[2].startsWith("HTTP/")) { 
                    while(true) { 
                        if(protocolReader.readLine().trim().equals("")) { 
                            break; // 空白行，接下来header部份，不处理
                        }
                    } 

                    // 送出 HTTP header
                    printStream.print("HTTP/1.0 302 FOUND\r\n"); 
                    printStream.print(
                             "Date: " + (new java.util.Date()) + "\r\n"); 
                    printStream.print("Server: httpRedirect v0.1\r\n"); 
                    printStream.print("Location: " + redirectUrl + "\r\n"); 
                    printStream.print("Content-type: text/html\r\n\r\n"); 
                } 
                else {
                    BufferedReader reader = 
                        new BufferedReader( 
                            new FileReader(movedHtml));
                    
                    String htmlContent = null; 
                    while((htmlContent = reader.readLine()) != null) { 
                        printStream.println(htmlContent); 
                    }
                    reader.close(); 
                }

                printStream.flush(); 
                clientSkt.close();
            }
        } 
        catch(IOException e) { 
            e.printStackTrace(); 
        } 
    } 
}

服务器只会显示客户连线端的IP位址，可以在客户端使用Telnet来测试看看结果：

$ telnet localhost 80
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
GET / HTTP/1.0

HTTP/1.0 302 FOUND
Date: Wed Jul 16 01:06:55 CST 2003
Server: httpRedirect v0.1
Location: http://www.caterpillar.onlyfun.net/phpBB2/
Content-type: text/html

Connection closed by foreign host.

$ telnet localhost 80
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
GET /
<html>
<head>
</head>
<body>
This site has been moved to: http://caterpillar.onlyfun.net
</body>
</html>
Connection closed by foreign host.