代理服务器

在开发中遇到这样的需求。使用中的系统（支持telnet的系统）因为某些原因不能做更改，而又需要增加一些功能。为了解决这个问题想了一办法，开发一个代理（注如果有更好的解决办法欢迎读者指出）将需要增加的需求在代理上消化。
下文就是代理的代码，代码用到apache commons net包：

package examples;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;

import org.apache.commons.net.telnet.EchoOptionHandler;
import org.apache.commons.net.telnet.InvalidTelnetOptionException;
import org.apache.commons.net.telnet.SuppressGAOptionHandler;
import org.apache.commons.net.telnet.TelnetClient;
import org.apache.commons.net.telnet.TerminalTypeOptionHandler;

public class TelnetClientExample implements Runnable {
	static TelnetClient tc = new TelnetClient();
	static Socket client; 
	public static void main(String[] args) throws IOException {
		TerminalTypeOptionHandler ttopt = new TerminalTypeOptionHandler("VT100", false, false, true, false);
		EchoOptionHandler echoopt = new EchoOptionHandler(true, false, true, false);
		SuppressGAOptionHandler gaopt = new SuppressGAOptionHandler(true, true, true, true);
		try {
			tc.addOptionHandler(ttopt);
			tc.addOptionHandler(echoopt);
			tc.addOptionHandler(gaopt);
		} catch (InvalidTelnetOptionException e) {
			System.err.println("Error registering option handlers: " + e.getMessage());
		}
		try {
			tc.connect("localhost", 21);
			OutputStream outstr = tc.getOutputStream();
			ServerSocket server = new ServerSocket(5678);
			client = server.accept();
			Thread reader = new Thread(new TelnetClientExample());
			reader.start();
			BufferedReader in = new BufferedReader(new InputStreamReader(client.getInputStream()));
			PrintWriter out = new PrintWriter(client.getOutputStream());
			String str = null;
			out.write("\n\r");
			out.flush();
			while ((str = in.readLine()) != null) {
				outstr.write(str.getBytes());
				outstr.write(13);
				outstr.write(10);
				outstr.flush();
			}
			client.close();
			
			try {
				tc.disconnect();
				System.out.println("tc.disconnect()");
			} catch (Exception e) {
				System.err.println("Exception while connecting:" + e.getMessage());
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	public void run() {
		InputStream instr = tc.getInputStream();
		try {
			byte[] buff = new byte[1024];
			int ret_read = 0;
			do {
				ret_read = instr.read(buff);
				if (ret_read > 0) {
					client.getOutputStream().write(buff, 0, ret_read);
					System.out.print("ret_read : " + ret_read + "  run() " + new String(buff, 0, ret_read));
				}
			} while (ret_read >= 0);
		} catch (Exception e) {
			System.err.println("Exception while reading socket:" + e.getMessage());
		}
		try {
			tc.disconnect();
		} catch (Exception e) {
			System.err.println("Exception while closing telnet:" + e.getMessage());
		}
	}
}

ps:以上代码仅为sample，只支持单用户，有兴趣的朋友可以更改代码让其支持多用户

以下为字符窗口的输入输出情况(服务器为ftp服务器)
代码运行后:win+r弹出程序运行框，输入cmd回车，接着输入telnet localhost 5678
user admin
501 Invalid character in command
user admin
331 User name okay, need password for admin.
pass admin
230 User logged in, proceed.
pwd
257 "/" is current directory.
help
214-The following commands are implemented.
ABOR  APPE  CDUP  CWD   DELE  HELP  LIST  MDTM
MKD   MODE  NLST  NOOP  PASS  PASV  PORT  PWD
QUIT  REST  RETR  RMD   RNFR  RNTO  SITE  SIZE
STAT  STOR  STOU  STRU  SYST  TYPE  USER
214 End of help.