向pop服务器提交用户名和密码以后，如何得到邮件的相关内容（包括完全收取下来）

import java.io.*; 
import java.net.*; 
import java.util.*; 
import javax.swing.JOptionPane;
import java.awt.event.*;

public class Pop3test implements Runnable
{
    Socket s = null;
    BufferedReader in  = null; 
    //BufferedWriter out = null;
    PrintWriter out = null;
    Vector vector = new Vector(); 
    mailtxt mt = null;
    boolean seemsg = false;
        
    public static void main(String[] args){
       
        Pop3test pop = new Pop3test();
        
     Thread h = new Thread(pop);
     h.start();
    }
    
  public void run(){
     getmail("pop.yeah.net","user","****",110,true);
                            ~~~~~用户名~~密码
  }
    
  public void getmail(String server,String user,String pwd,int port,boolean now){   
     try{    
        
        s = new Socket(server,port);
        in  = new BufferedReader(new InputStreamReader(s.getInputStream())); 
        //out = new BufferedWriter(new OutputStreamWriter(s.getOutputStream())); 
        out = new PrintWriter(new OutputStreamWriter(s.getOutputStream()));
        seemsg = now;
        String str;
       // System.out.println(server+" pop3");
        str = in.readLine();
        System.out.println("USER :"+user); 
        if (str.indexOf("OK")-1){
                  String maildate = str.substring(n+11,str.length()-n);
                  System.out.println("Message-ID:"+maildate);
                  received = true;
                  continue;
               }
               n = str.indexOf("To:");
               if (n>-1){
                  String maildate = str.substring(n+3,str.length()-n);
                  System.out.println("To :"+maildate);
                  received = true;
                  continue;
               }
               n = str.indexOf("From:");
               if (n>-1){
                  String maildate = str.substring(n+5,str.length()-n);
                  System.out.println("From :"+maildate);
                  received = true;
                  continue;
               }
               n = str.indexOf("Subject:");
               if (n>-1){
                  String maildate = new String(str.substring(n+8,str.length()-n).getBytes("gb2312"));
                 // String maildate = str.substring(n+8,str.length()-n);
                  System.out.println("Subject :"+maildate);
                  received = true;
                  continue;
               }
               n = str.indexOf("X-Priority:");
               if (n>-1){
                  String maildate = str.substring(n+11,str.length()-n);
                  System.out.println("X-Priority:"+maildate);
                  received = true;
                  continue;
               }
               n = str.indexOf("X-Originating-IP:");
               if (n>-1){
                  String maildate = str.substring(n+17,str.length()-n);
                  System.out.println("X-Originating-IP:"+maildate);
                  received = true;
                  continue;
               }
               n = str.indexOf("Sender:");
               if (n>-1){
                  String maildate = new String(str.substring(n+7,str.length()-n).getBytes("gb2312"));
                  //String maildate = str.substring(n+7,str.length()-n);
                  System.out.println("Sender :"+maildate);
                  received = true;
                  continue;
               }
               if (!received){
                   continue;
               }
               str = new String(str.getBytes("gb2312"));
               //str = new String(bbb);
               if (seemsg){
                  result += str + "n"; 
               }   
           }  
           
           if (seemsg){
              System.out.println(result);
           }   
           System.out.println("^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^");
           
           return true;
        }catch(IOException io){   
           System.out.println(io.toString());
           return false;
        } 
         
    }    

    
}

不是有javamail api吗？
干嘛要用低层的？