pop3clientdemo.java

Java网络编程与分布式计算, 主要分析java网络各方面的编程, 提供许多实用安全

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

// Chapter 8, Listing 2
public class Pop3ClientDemo
{
  protected int port = 110;
  protected String hostname = "localhost";
  protected String username = "";
  protected String password = "";

  protected Socket socket;
  protected BufferedReader br;
  protected PrintWriter pw;

  // Constructs a new instance of the POP3 client
  public Pop3ClientDemo() throws Exception
  {
    try
    {
	   // Get user input
       getInput();

	   // Get mail messages
       displayEmails();
    }
    catch(Exception e)
    {
        System.err.println ("Error occured - details follow");
		e.printStackTrace();
        System.out.println(e.getMessage());
    }
  }

  // Returns TRUE if POP response indicates success, FALSE if failure
  protected boolean responseIsOk() throws Exception
  {
    String line = br.readLine();
    System.out.println("< "+line);
    return line.toUpperCase().startsWith("+OK");
  }

  // Reads a line from the POP server, and displays it to screen
  protected String readLine(boolean debug) throws Exception
  {
    String line = br.readLine();

	// Append a < character to indicate this is a server protocol response
    if (debug)
		System.out.println("< "+line);
    else
		System.out.println(line);
    return line;
  }

  // Writes a line to the POP server, and displays it to the screen
  protected void writeMsg(String msg) throws Exception
  {
    pw.println(msg);
    pw.flush();
    System.out.println("> "+msg);
  }

  // Close all writers, streams and sockets
  protected void closeConnection() throws Exception
  {
    pw.flush();
    pw.close();
    br.close();
    socket.close();
  }

  // Send the QUIT command, and close connection
  protected void sendQuit() throws Exception
  {
    System.out.println("Sending QUIT");
    writeMsg("QUIT");
    readLine(true);

    System.out.println("Closing Connection");
    closeConnection();
  }


  // Display emails in a message
  protected void displayEmails() throws Exception
  {
	BufferedReader userinput = new BufferedReader( new InputStreamReader (System.in) );

    System.out.println("Displaying mailbox with protocol commands and responses below");
    System.out.println("--------------------------------------------------------------");

	// Open a connection to POP3 server
    System.out.println("Opening Socket");
    socket = new Socket(this.hostname, this.port);

    br = new BufferedReader(new InputStreamReader(socket.getInputStream()));
    pw = new PrintWriter(new OutputStreamWriter(socket.getOutputStream()));

	// If response from server is not okay
    if(! responseIsOk())
	{
		socket.close();
		throw new Exception("Invalid POP3 Server");
	}

	// Login by sending USER and PASS commands
    System.out.println("Sending username");
    writeMsg("USER "+this.username);
    if(!responseIsOk())
    {
      sendQuit();
      throw new Exception("Invalid username");
    }

    System.out.println("Sending password");
    writeMsg("PASS "+this.password);
    if(!responseIsOk())
    {
      sendQuit();
      throw new Exception("Invalid password");
    }


	// Get mail count from server ....
    System.out.println("Checking mail");
    writeMsg("STAT");

	// ... and parse for number of messages
    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("Retrieving 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
  {
    Pop3ClientDemo client = new Pop3ClientDemo();
  }

  // Read user input
  protected void getInput() throws Exception
  {
    String data=null;
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    System.out.print("Please enter POP3 server hostname:");
    data = br.readLine();
    if(data == null || data.equals("")) hostname="localhost";
    else
		hostname=data;

    System.out.print("Please enter mailbox username:");
    data = br.readLine();
    if(!(data == null || data.equals("")))
		username=data;

    System.out.print("Please enter mailbox password:");
    data = br.readLine();
    if(!(data == null || data.equals("")))
		password=data;
  }
}