发送E-mail

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为了发送E-mail，必须建立一个到端口25（即SMTP端口）的套接字连接。

一旦连接到服务器，就可以发送一个邮件报头（采用SMTP格式，该格式很容易生成）。紧随其后的是邮件消息。详细操作步骤如下

  1. 打开一个到达主机的套接字：
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Socket s=new Socket("mail.yourserver.com",25);
PrintWriter out = new PrintWriter(s.getOutputStream());

  1. 发送一下消息到打印流：

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    HELO sending host
    MAIL FROM:<sender e-mail address>
    RCPT TO: <recipient e-mail address>
    DATA
    mail message
    {any number of lines}
    ...
    QUIT

    SMTP规范规定，每一行都要以\r再紧跟一个\n来结尾。

    有些SMTP服务器并不检查信息的真实性，你可以随意填写任何你喜欢的发件人名字。

相比几下，有个更为简单的E-mail发送方式——使用JavaMail API，在JavaMail API中，你只需要简单地调用下面这个方法，就可以发送一条邮件了，该类库负责实现邮件协议、认证和附件处理等。

示例程序如下：

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import java.awt.*;
import java.awt.event.*;
import java.util.*;
import java.net.*;
import java.io.*;
import javax.swing.*;
public class MailTest
{
   public static void main(String[] args)
   {
      EventQueue.invokeLater(new Runnable()
         {
            public void run()
            {
               JFrame frame = new MailTestFrame();
               frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
               frame.setVisible(true);
            }
         });
   }
}
class MailTestFrame extends JFrame
{
   public MailTestFrame()
   {
      setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);
      setTitle("MailTest");

      setLayout(new GridBagLayout());

      add(new JLabel("From:"), new GBC(0, 0).setFill(GBC.HORIZONTAL));

      from = new JTextField(20);
      add(from, new GBC(1, 0).setFill(GBC.HORIZONTAL).setWeight(100, 0));

      add(new JLabel("To:"), new GBC(0, 1).setFill(GBC.HORIZONTAL));

      to = new JTextField(20);
      add(to, new GBC(1, 1).setFill(GBC.HORIZONTAL).setWeight(100, 0));

      add(new JLabel("SMTP server:"), new GBC(0, 2).setFill(GBC.HORIZONTAL));

      smtpServer = new JTextField(20);
      add(smtpServer, new GBC(1, 2).setFill(GBC.HORIZONTAL).setWeight(100, 0));

      message = new JTextArea();
      add(new JScrollPane(message), new GBC(0, 3, 2, 1).setFill(GBC.BOTH).setWeight(100, 100));

      comm = new JTextArea();
      add(new JScrollPane(comm), new GBC(0, 4, 2, 1).setFill(GBC.BOTH).setWeight(100, 100));

      JPanel buttonPanel = new JPanel();
      add(buttonPanel, new GBC(0, 5, 2, 1));

      JButton sendButton = new JButton("Send");
      buttonPanel.add(sendButton);
      sendButton.addActionListener(new ActionListener()
         {
            public void actionPerformed(ActionEvent event)
            {
               new SwingWorker<Void, Void>()
               {
                  protected Void doInBackground() throws Exception
                  {
                     comm.setText("");
                     sendMail();
                     return null;
                  }
               }.execute();
            }
         });
   }
   public void sendMail()
   {
      try
      {
         Socket s = new Socket(smtpServer.getText(), 25);

         InputStream inStream = s.getInputStream();
         OutputStream outStream = s.getOutputStream();

         in = new Scanner(inStream);
         out = new PrintWriter(outStream, true /* autoFlush */);

         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();
         send(message.getText());
         send(".");
         receive();
         s.close();
      }
      catch (IOException e)
      {
         comm.append("Error: " + e);
      }
   }
   public void send(String s) throws IOException
   {
      comm.append(s);
      comm.append("\n");
      out.print(s.replaceAll("\n", "\r\n"));
      out.print("\r\n");
      out.flush();
   }
   public void receive() throws IOException
   {
      String line = in.nextLine();
      comm.append(line);
      comm.append("\n");
   }

   private Scanner in;
   private PrintWriter out;
   private JTextField from;
   private JTextField to;
   private JTextField smtpServer;
   private JTextArea message;
   private JTextArea comm;

   public static final int DEFAULT_WIDTH = 300;
   public static final int DEFAULT_HEIGHT = 300;
}
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import java.awt.*;

public class GBC extends GridBagConstraints 
{
   public GBC(int gridx, int gridy)
   {
      this.gridx = gridx;
      this.gridy = gridy;
   }
   public GBC(int gridx, int gridy, int gridwidth, int gridheight)
   {
      this.gridx = gridx;
      this.gridy = gridy;
      this.gridwidth = gridwidth; 
      this.gridheight = gridheight; 
   }
   public GBC setAnchor(int anchor) 
   { 
      this.anchor = anchor; 
      return this;
   }
   public GBC setFill(int fill) 
   { 
      this.fill = fill; 
      return this;
   }
   public GBC setWeight(double weightx, double weighty) 
   { 
      this.weightx = weightx; 
      this.weighty = weighty; 
      return this;
   }
   public GBC setInsets(int distance) 
   { 
      this.insets = new Insets(distance, distance, distance, distance);
      return this;
   }
   public GBC setInsets(int top, int left, int bottom, int right) 
   { 
      this.insets = new Insets(top, left, bottom, right);
      return this;
   }

   public GBC setIpad(int ipadx, int ipady) 
   { 
      this.ipadx = ipadx; 
      this.ipady = ipady; 
      return this;
   }
}
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