Java 網路程式設計 -- Telnet

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在本文中，我們設計了一個稱為 Telnet.java 的程式，以實作 Telnet 的功能。該程式同時是 Client 端，也是 Server 端，因此其架構上是一個 P2P 的程式。

使用時，必須先用 java Telnet server 指令執行伺服端，然後再用 java Telnet <server_ip> 指令執行 Client 端，如此就可以在 Client 端對伺服端下指令，就好像 Server 端的電腦完全受到 Client 端操控一般。其程式如以下的 Telnet.java 所示。

程式: Telnet.java

import java.net.*;
import java.io.*;
 
/* Protocol :    Client ----------- Server
 *
 *                       <---------  <path> (single line)
 * (single line)  <cmd>  ---------->
 *                       <---------  <output> (several lines)
 *                         <---------     ==end== (single line)
 *
 *                another session started again
 *
 *                       <---------  <path> (single line)
 *                       .....
 */
 
public class Telnet {
    static int port = 23;
    static final String endMsg = "==end==";
 
    public static void main(String[] args) throws Exception {
        if (args[0].equals("server"))
            runServer();
        else if (args[0].equals("client"))
            runClient(args[1], port);
        else
            System.out.println("Client : java Telnet client ip\r\n"+
                               "Server : java Telnet server");
    }    
 
    public static void runClient(String host, int port) throws Exception {
        System.out.println("Host " + host + "; port " + port);
        Socket socket = new Socket(host, port);
        new CommandClient(socket).start();
        System.out.println("Connected OK");
    }
 
    public static void runServer() throws Exception {
        ServerSocket server = new ServerSocket(port);  // 建立ServerSocket物件
        while (true)
        {  // 建立客戶端Socket物件
            Socket socket = server.accept();
            System.out.println("Accept Connection From : " + socket.getInetAddress());
            new CommandServer(socket).start();
        }
    }    
}
 
class Command {
    ProcessBuilder pb;
 
    Command() {
        pb = new ProcessBuilder();
        pb.directory(new File("."));
    }
 
    public String exec(String command) throws Exception {
        String outMsg = "", errMsg = "";
        if (command.startsWith("cd ")) {
            String path = command.substring(3);
            if (path.equals("\\")) {
                String tPath = getPath();
                String rootPath = tPath.substring(0,3);
                File root = new File(rootPath);
                pb.directory(root);
            } else {            
                try {
                    File dir = new File(pb.directory(), path);
                    pb.directory(dir);
                } catch (Exception e) {
                    errMsg = "Error: "+e.toString();
                }
            }
        } else {
            String[] cmd = { "cmd.exe", "/C", command };
            pb.command(cmd);
            Process process = pb.start();
             // 取得命令執行的結果串流結果傳回給 Client.
            //   請注意 process.getInputStream() 取得的是 command 的輸出串流，
            //  被重導到輸入串流以利讀取的結果 (這在概念上很怪，但確實如此)
            outMsg = readAll(process.getInputStream());
 
             // 取得命令執行的錯誤串流結果傳回給 Client.
            errMsg = readAll(process.getErrorStream());
            process.waitFor();                     // 等待命令執行完畢
        }
        return outMsg+errMsg;
    }
 
    public String getPath() throws Exception {
        return pb.directory().getCanonicalPath();
    }
 
    public String readAll(InputStream is) throws Exception {
        StringBuffer rzText = new StringBuffer();
        BufferedReader in = new BufferedReader(new InputStreamReader(is));
        String line;
        while ((line = in.readLine()) != null) {
            rzText.append(line+"\r\n");
        }
        return rzText.toString();
    }         
}
 
class CommandServer extends Thread {
    Socket socket;
    BufferedReader in;
    PrintStream out;
    Command command;
 
    public CommandServer(Socket s) throws Exception {
        socket = s;
        in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
        out = new PrintStream(socket.getOutputStream());
        command = new Command();
    }
 
    public void run() {
      try {
         while (true) {
             out.println(command.getPath());     // set path to client
            out.flush();
             String cmd = in.readLine();            // read command from client
             System.out.println(socket.getInetAddress()+" $ "+cmd);
             String rzMsg = command.exec(cmd);    // execute command
             out.print(rzMsg);
            out.println(Telnet.endMsg);            // 輸出結束訊息
            out.flush();
        }
      } catch (Exception e) { e.printStackTrace(); }
    }
}
 
class CommandClient extends Thread {
    Socket socket;
    BufferedReader in, stdin;
    PrintStream out;
 
    public CommandClient(Socket s) throws Exception {
        socket = s;
        in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
        out = new PrintStream(socket.getOutputStream());
        stdin = new BufferedReader(new InputStreamReader(System.in));
    }
 
    public void run() {
      try {
        System.out.println("Accept from : " + socket.getInetAddress());
         while (true) {
             String path = in.readLine();        // read path from server
             System.out.print(socket.getInetAddress()+" $ "+path+">");
             String cmd = stdin.readLine();        // read command from console
             out.println(cmd);                    // send command to server
             while (true) {                        // read output of command from server
                 String line = in.readLine();
                 if (line.equals(Telnet.endMsg))
                     break;
                 System.out.println(line);
             }
        }
      } catch (Exception e) { e.printStackTrace(); }
    }
}

執行結果

編譯

D:\java>javac Telnet.java

伺服端：Telnet Server

D:\java>java Telnet server
Accept Connection From : /127.0.0.1
/127.0.0.1 $ SET JAVA_HOME
/127.0.0.1 $ dir Telnet.java

伺服端：Telnet Client 127.0.0.1

D:\java>java Telnet client 127.0.0.1
Host 127.0.0.1; port 23
Connected OK
Accept from : /127.0.0.1
/127.0.0.1 $ D:\java>SET JAVA_HOME
JAVA_HOME=C:\Program Files\liftweb-1.0.1\jre
/127.0.0.1 $ D:\java>dir Telnet.java
 磁碟區 D 中的磁碟沒有標籤。
 磁碟區序號:  AC7E-23A4

 D:\java 的目錄

2007/05/16  上午 11:23             4,862 Telnet.java
               1 個檔案           4,862 位元組
               0 個目錄   8,863,780,864 位元組可用

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page revision: 0, last edited: 08 Nov 2010 02:22

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訊息

程式: Telnet.java

執行結果

編譯

伺服端：Telnet Server

伺服端：Telnet Client 127.0.0.1

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