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

public class AccessPOP3
{
   private static final int POP3_PORT = 110;

   public static void main(String[] args)
   {
	   Socket            mailSocket;
	   BufferedReader    socketInput;
	   DataOutputStream  socketOutput;
      
	   //檢查命令行參數
	   if (args.length < 4)
	   {
		   System.out.println(
			   "\nUsage: AccessPOP3 <host> <username> <password> <command>");
		   System.out.println("Parameters:");
		   System.out.println(
			   "\thost = Name or IP address of POP3 mail Server.");
		   System.out.println("\tusername = Account on POP3 mail Server.");
		   System.out.println("\tpassword = Password on POP3 mail Server.");
		   System.out.println("\tcommand =  POP3 Command.");
		   System.out.println("Example:");
		   System.out.println(
			   "\tjava AccessPOP3 hotmail.yn.cninfo.net yshf 111111 STAT");
		   System.out.println(
			   "\tjava AccessPOP3 hotmail.yn.cninfo.net yshf 111111 LIST 2");

		   System.exit(1);	//退出
	   }

	   try {
		   //連接POP3郵件服務器
		   System.out.println("Connecting ...");
		   mailSocket = new Socket(args[0], POP3_PORT);

		   //創建socket的輸入/輸出流，用于網絡通信
		   socketInput = new BufferedReader(
			   new InputStreamReader(mailSocket.getInputStream()));
		   socketOutput = new DataOutputStream(mailSocket.getOutputStream());

		   // 獲得POP3郵件服務器的初始信息
		   DisplayReply(socketInput);

		   //登錄POP3郵件服務器
		   System.out.println("USER " + args[1]);
		   socketOutput.writeBytes("USER " + args[1] + "\r\n");
		   DisplayReply(socketInput);
		   System.out.println("PASS " + args[2]);
		   socketOutput.writeBytes("PASS " + args[2] + "\r\n");
		   DisplayReply(socketInput);

		   //發送請求，以回車和換行（<CRLF>）結尾
		   for (int i = 3; i < args.length; i++)
			   socketOutput.writeBytes(args[i] + " ");
		   socketOutput.writeBytes("\r\n");

		   DisplayReply(socketInput);

		   //退出POP3郵件服務器
		   System.out.println("QUIT " + "\r\n");

		   //關閉BufferedReader和DataOutputStream對象
		   socketInput.close();
		   socketOutput.close();
		   //關閉socket連接
		   mailSocket.close();
	   }catch(Exception theException) {
		   System.out.println(theException);
	   }
		   System.exit(0);	//退出

   }

   //接收并顯示POP3郵件服務器的響應信息
   private static void DisplayReply(BufferedReader reader)
	   throws IOException, Exception
   {	   
	   String s;

	   s = reader.readLine();
	   System.out.println(s);
   }
}