详解电子邮件的POP3协议及最小化实现

package com.gloomyfish.sslsocket.study;
 
import java.io.BufferedReader;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
 
import javax.net.ssl.SSLSocket;
import javax.net.ssl.SSLSocketFactory;
 
public class POP3Client {
  private static DataOutputStream writer;
  public static void main(String[] args) throws Exception
  {
    int delay = 6000;// give enough delay to get response message from POP server
    SSLSocket sock = (SSLSocket)((SSLSocketFactory)SSLSocketFactory.getDefault()).createSocket("pop.gmail.com", 995);
    final BufferedReader br = new BufferedReader(new InputStreamReader(sock.getInputStream()));
    (new Thread(new Runnable()
    {
      public void run()
      {
        try
        {
          String line;
          while((line = br.readLine()) != null)
            System.out.println(" S: "+line);
        }
        catch (IOException e)
        {
          e.printStackTrace();
        }
      }
    })).start();
    writer = new DataOutputStream(sock.getOutputStream());
    
    // start to AUTHORIZATION State
    send("USER YOUREMAILID\r\n");
    Thread.sleep(delay);
    send("PASS YOURPASSWORD\r\n");
    Thread.sleep(delay);
    // end AUTHORIZATION State
    
    // start <<The TRANSACTION State>>
    send("STAT\r\n"); // check new arrived mail
    Thread.sleep(delay);
    
    // List Mail
    send("LIST 1\r\n"); // check new arrived mail
    Thread.sleep(delay);
    
    // Fetch the message here [RETR <SP> msg CRLF]
    send("RETR 1\r\n"); // check new arrived mail
    Thread.sleep(delay);
    
    // DELET
    send("DELE 1\r\n"); // check new arrived mail
    Thread.sleep(delay);
    
    // UNMARKER THE DELETED EMAIL
    send("RSET\r\n"); // check new arrived mail
    Thread.sleep(delay);
    // end The TRANSACTION State
    
    // issue the [quit] command from client.
    send("QUIT\r\n");
    Thread.sleep(delay);
  }
  
  private static void send(String s) throws Exception
  {
    writer.writeBytes(s);
    System.out.println(" C: "+s);
  }
 
}