pop3.java~1~

用POP3协议来实现收发邮件的Java程序

package pop3;

/**
 * <p>Title: </p>
 * <p>Description: </p>
 * <p>Copyright: Copyright (c) 2004</p>
 * <p>Company: </p>
 * @author not attributable
 * @version 1.0
 */
import java.io.*;
import java.net.*;
import java.util.*;
public class pop3 {
  protected int port=110;
  protected String hostname="localhost";
  protected String password="";
  protected String username="";
  protected Socket socket;
  protected BufferedReader br;
  protected PrintWriter pw;
  public pop3() throws Exception{
  try
  {
    getInput();      //获得用户输入
    displayEmails();       //获得邮件信息
  }
  catch(Exception e)      //出错处理
  {
    System.err.println("error occured -details follow");
    e.printStackTrace();
    System.out.println(e.getMessage());
  }
  }
  protected boolean responseIsOK() throws Exception //如果pop相应就返回true，否则返回false
  {
    String line=br.readLine();   //获得server的反应
    System.out.println("<"+line);
    return line.toUpperCase().startsWith("+ok");
  }
  protected String readline(boolean debug) throws Exception  //从server读，并且显示
  {
    String line=br.readLine();       //加入<表示是server的控制反应
    if(debug)
      System.out.println("<"+line);
      else
        System.out.println(line);
        return line;
  }
  protected void writeMsg(String msg)throws Exception  //向服务器写消息
  {
    pw.println(msg);
    pw.flush();
    System.out.println(">"+msg);     //控制命令用>开头
  }
  protected void closeConnection() throws Exception  //关闭所有的writers，sockets，随treams
  {
    pw.flush();
    pw.close();
    br.close();
    socket.close();
  }
  protected void sendQuit() throws Exception  //发送关闭命令
  {
    System.out.println("sending QUIT");
    writeMsg("QUIT");
    readline(true);
    System.out.println("closing connection");
    closeConnection();
  }
  protected void displayEmails() throws Exception  //显示邮件相关信息
  {
    BufferedReader userinput=new BufferedReader(new InputStreamReader(System.in));
    System.out.println("dispalying mailbox with protocol commadns and responses below");
    System.out.println("--------------------------------------");
    System.out.println("opening socket");
    System.out.println(this.hostname+this.username+this.password);
    socket=new Socket(this.hostname,this.port);
    br=new BufferedReader(new InputStreamReader(socket.getInputStream()));  //socket的输入输出流
    pw=new PrintWriter(new OutputStreamWriter(socket.getOutputStream()));
    if(!responseIsOK())  //测试连接是否正常
    {
      socket.close();
      throw new Exception("invalid pop3 server");
    }
    System.out.println("sending username");
    writeMsg("USER:"+this.username);  //写入用户名
    if(!responseIsOK())   //测试用户名是否正确
    {
      sendQuit();
      throw new Exception("invalid username");
    }
    System.out.println("sending password");
    writeMsg("PASS:"+this.password);  //写入密码
    if(!responseIsOK())     //测试密码是否正确
    {
      sendQuit();
      throw new Exception("invalid password");
    }
    System.out.println("checking mail");  //从server处得到邮件数量
    writeMsg("STAT");
    String line=readline(true);
    StringTokenizer tokens=new StringTokenizer(line,"");
    tokens.nextToken();
    int messages=Integer.parseInt(tokens.nextToken());
    int maxsize=Integer.parseInt(tokens.nextToken());
    if(messages==0)
    {
      System.out.println("there are no messages");
      sendQuit();
      return;
    }
    System.out.println("there are"+messages+"messages");
    System.out.println("press enter to continue");
    userinput.readLine();
    for(int i=1;i<=messages;i++)
    {
      System.out.println("retriving message number"+i);
      writeMsg("RETR"+i);
      System.out.println("------------------");
      line=readline(false);
      while(line!=null&&!line.equals("."))
      {
        line=readline(false);
      }
      System.out.println("-------------------");
      System.out.println("press enter to continue."+"to stop,type Q then enter");
      String response=userinput.readLine();
      if(response.toUpperCase().startsWith("Q"))
        break;
    }
    sendQuit();
  }
  public static void main(String[] args) throws Exception{
    pop3 client=new pop3();
  }
  protected void getInput()throws Exception
  {
    String data=null;
    BufferedReader br=new BufferedReader(new InputStreamReader(System.in) );
    System.out.println("please enter pop3 server hostname");
    data=br.readLine();
    if(data==null||data.equals(""))hostname="localhost";
      else
        hostname=data;
        System.out.println("please enter mailbox username:");
        data=br.readLine();
        if(!(data==null||data.equals("")))
          username=data;
          System.out.println("please enter mailbox password:");
          data=br.readLine();
          if(!(data==null||data.equals("")))
            password=data;
  }
}