java网络编程三：基于SMTP的邮件发送客户端

1、SMTP简介

2、发送过程

3、源代码示例

 "font-size:16px;">package demo.net;

 import java.awt.BorderLayout;
 import java.awt.GridLayout;
 import java.awt.event.ActionEvent;
 import java.awt.event.ActionListener;
 import java.io.IOException;
 import java.io.PrintWriter;
 import java.net.InetAddress;
 import java.net.Socket;
 import java.util.Scanner;

 import javax.swing.*;

 /*
  * 发送邮件客户端
  */
 public class SendMail extends JFrame {
     private JTextField from;
     private JTextField to;
     private JTextField server;
     private JTextArea message;
     private JTextArea comm;
     private Scanner in;
     private PrintWriter out;

     public SendMail() {
         // 设置frame
         setSize(500, 600);
         setTitle("send mail");
         setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
         setVisible(true);
         this.setLocationRelativeTo(null);

         // 往frame中添加组件
         JPanel p1 = new JPanel(new GridLayout(3, 2));
         p1.add(new JLabel("from:"));
         from = new JTextField(20);
         p1.add(from);

         p1.add(new JLabel("to:"));
         to = new JTextField(20);
         p1.add(to);

         p1.add(new JLabel("SMTP server:"));
         server = new JTextField(20);
         p1.add(server);
         add(p1, BorderLayout.NORTH);

         JPanel p2 = new JPanel(new GridLayout(2, 1));
         message = new JTextArea();
         p2.add(new JScrollPane(message));

         comm = new JTextArea();
         comm.setEditable(false);
         p2.add(new JScrollPane(comm));
         add(p2, BorderLayout.CENTER);

         JPanel p3 = new JPanel();
         JButton sendButton = new JButton("Send");
         p3.add(sendButton);
         add(p3, BorderLayout.SOUTH);

         // 给发送按钮注册监听器
         sendButton.addActionListener(new ActionListener() {
             @Override
             public void actionPerformed(ActionEvent e) {
                 comm.setText("");
                 sendMail(server.getText().trim(), from.getText().trim(), to
                         .getText().trim(), message.getText());
             }
         });
     }

     // 发送邮件
     public void sendMail(String server, String from, String to, String message) {
         try {
             Socket s = new Socket(server, 25);
             try {
                 in = new Scanner(s.getInputStream());
                 out = new PrintWriter(s.getOutputStream(), true/* 表示自动刷新 */);
                 String hostName = InetAddress.getLocalHost().getHostName();

                 receive();

                 send("HELLO" + hostName);// 握手，成功返回220表示服务就绪
                 receive();

                 send("MAIL FROM:<" + from + ">");//发件人邮箱
                 receive();

                 send("RCPT TO:<" + to + ">");//收件人邮箱
                 receive();

                 send("DATA");//表示开始发邮件内容了
                 receive();

                 send(message);//发送邮件你内容
                 send(".");
                 receive();
                 send("QUIT");
             } finally {
                 s.close();
             }
         } catch (IOException e) {
             comm.append("Error: " + e);
         }
     }

     // 发送
     private void send(String s) {
         comm.append(s + '\n');
         out.print(s);
         out.print("\r\n");
         out.flush();
     }

     // 接收
     private void receive() {
         comm.append(in.nextLine() + '\n');
     }

     public static void main(String[] args) {
         new SendMail();
     }
 }