请教一个发邮件的程序(30分)

import java.awt.*;
import java.awt.event.*;
import java.util.*;
import java.net.*;
import java.io.*;
import javax.swing.*;
/**
This program shows how to use sockets to send plain text
mail messages.
*/
public class MailTest
{
public static void main(String[] args)
{
JFrame frame = new MailTestFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.show();
}
}
/**
The frame for the mail GUI.
*/
class MailTestFrame extends JFrame
{
public MailTestFrame()
{
setSize(WIDTH, HEIGHT);
setTitle("MailTest");
getContentPane().setLayout(new GridBagLayout());
GridBagConstraints gbc = new GridBagConstraints();
gbc.fill = GridBagConstraints.HORIZONTAL;
gbc.weightx = 0;
gbc.weighty = 0;
gbc.weightx = 0;
add(new JLabel("From:"), gbc, 0, 0, 1, 1);
gbc.weightx = 100;
from = new JTextField(20);
add(from, gbc, 1, 0, 1, 1);
gbc.weightx = 0;
add(new JLabel("To:"), gbc, 0, 1, 1, 1);
gbc.weightx = 100;
to = new JTextField(20);
add(to, gbc, 1, 1, 1, 1);
gbc.weightx = 0;
add(new JLabel("SMTP server:"), gbc, 0, 2, 1, 1);
gbc.weightx = 100;
smtpServer = new JTextField(20);
add(smtpServer, gbc, 1, 2, 1, 1);

gbc.fill = GridBagConstraints.BOTH;
gbc.weighty = 100;
message = new JTextArea();
add(new JScrollPane(message), gbc, 0, 3, 2, 1);
communication = new JTextArea();
add(new JScrollPane(communication), gbc, 0, 4, 2, 1);
gbc.weighty = 0;
JButton sendButton = new JButton("Send");
sendButton.addActionListener(new
ActionListener()
{
public void actionPerformed(ActionEvent evt)
{
new
Thread()
{
public void run()
{
sendMail();
}
}.start();
}
});
JPanel buttonPanel = new JPanel();
buttonPanel.add(sendButton);
add(buttonPanel, gbc, 0, 5, 2, 1);
}
/**
Add a component to this frame.
@param c the component to add
@param gbc the grid bag constraints
@param x the grid bax column
@param y the grid bag row
@param w the number of grid bag columns spanned
@param h the number of grid bag rows spanned
*/
private void add(Component c, GridBagConstraints gbc,
int x, int y, int w, int h)
{
gbc.gridx = x;
gbc.gridy = y;
gbc.gridwidth = w;
gbc.gridheight = h;
getContentPane().add(c, gbc);
}
/**
Sends the mail message that has been authored in the GUI.
*/
public void sendMail()
{
try
{
Socket s = new Socket(smtpServer.getText(), 25);
out = new PrintWriter(s.getOutputStream());
in = new BufferedReader(new
InputStreamReader(s.getInputStream()));
String hostName
= InetAddress.getLocalHost().getHostName();
receive();
send("HELO " + hostName);
receive();
send("MAIL FROM: <" + from.getText() + ">");
receive();
send("RCPT TO: <" + to.getText() + ">");
receive();
send("DATA");
receive();
StringTokenizer tokenizer = new StringTokenizer(
message.getText(), "/n");
while (tokenizer.hasMoreTokens())
send(tokenizer.nextToken());
send(".");
receive();
s.close();
}
catch (IOException exception)
{
communication.append("Error: " + exception);
}
}
/**
Sends a string to the socket and echoes it in the
communication text area.
@param s the string to send.
*/
public void send(String s) throws IOException
{
communication.append(s);
communication.append("/n");
out.print(s);
out.print("/r/n");
out.flush();
}
/**
Receives a string from the socket and displays it
in the communication text area.
*/
public void receive() throws IOException
{
String line = in.readLine();
if (line != null)
{
communication.append(line);
communication.append("/n");
}
}
private BufferedReader in;
private PrintWriter out;
private JTextField from;
private JTextField to;
private JTextField smtpServer;
private JTextArea message;
private JTextArea communication;
public static final int WIDTH = 300;
public static final int HEIGHT = 300;

}
这是一个发送E-mail的程序,实际上不能用可能要密码和帐户登陆,但我想知道其原理,如果能用是如何发送的我根本就看不出来那里实现了发送的功能也就是如何通过SMTP服务器发到别人的邮箱里,

用的是Socket，按照SMTP协议接受和发送数据。你看send和receive方法，用到Socket的输入输出流。

对 其实原理的东西还是socket的东西
它只是把你要发送的东西，按照smtp的协议，变成流的形式发送过去

参考
http://www.java-cn.com