(四) 发送E-mail

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。简单邮件传输协议用于描述E-mail消息的格式。
可以连接到任何一个提供SMTP服务的服务器，不过需要确定服务器是否愿意接受请求。SMTP服务器通常总是愿意发送来自任何人的E-mail，但是由于垃圾邮件泛滥，大多数服务器都内置有检查功能，它们只接受那些来自它们所信任的用户或IP地址段的请求。
一旦连接到服务器，就可以发送一个邮件报头(采用SMTP格式)。紧随其后是邮件消息。
操作的详细过程:
1.打开一个到达主机的套接字:

    Socket socket = new Socket("mail.mailserver.com", 25);
    PrintWriter out = new PrintWriter(socket.getOutputStream());

 

2.发送以下信息到输出流
    HELO sending host
    MAIL FROM: <sender e-mail address>
    RCPT TO: <recipient e-mail address>
    DATA
    mail message
    (any number of lines)
    .
    QUIT
e.g.

    OutputStream outStream = socket.getOutputStream();
    PrintWriter out = new PrintWriter(new OutputStreamWriter(outStream, "utf-8"), true);
    String hostName = InetAddress.getLocalHost().getHostName();
    out.print("HELO " + hostName + "\r\n");
    out.print("MAIL FROM: <" + from.getText() + ">\r\n");
    out.print("RCPT TO: <" + to.getText() + ">\r\n");
    out.print("DATA\r\n");
    out.print(("the mail message...\n").replaceAll("\n", "\r\n"));
    out.print(".\r\n");
    out.print("QUIT\r\n"));

 

3.SMTP规范(RFC 821)规定，每行都要以\r再紧跟一个\n来结尾。
4.有些SMTP服务器并不检查信息的真实性，可以随意填写任何喜欢使用的发件人名字。
5.现在大多数SMTP服务器都会检查守信IP，其他服务器将使用"SMTP之前先POP"规范，即要求在发送任何消息之前先下载你的E-mail，即要求提供密码。

 

 

DEMO

import java.awt.EventQueue;

import javax.swing.JFrame;

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);
			}
		});
	}
}

 

/**
 * 该程序会因为受限于SMTP服务器检测IP地址的原因，导致失败
 */
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.util.Scanner;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.SwingWorker;

public class MailTestFrame extends JFrame {
	
	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;
	
	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(){

			@Override
			public void actionPerformed(ActionEvent e) {
				new SwingWorker<Void, Void>(){
					protected Void doInBackground() throws Exception{
						comm.setText("");
						sendMail();
						return null;
					}
				}.execute();
			}
			
		});
	}
	
	public void sendMail(){
		try{
//			Socket socket = new Socket(smtpServer.getText(), 25);
			Socket socket = new Socket();
			socket.connect(new InetSocketAddress(smtpServer.getText(), 25), 2000);
			try{
				InputStream inStream = socket.getInputStream();
				OutputStream outStream = socket.getOutputStream();
				
				in = new Scanner(inStream);
				out = new PrintWriter(new OutputStreamWriter(outStream, "utf-8"), true);
				
				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();
			}finally{
				socket.close();
			}
		}catch(IOException e){
			comm.append("Error: " + e);
		}
	}

	private void send(String str) throws IOException{
		comm.append(str);
		comm.append("\n");
		out.print(str.replaceAll("\n", "\r\n"));
		out.flush();
	}

	private void receive() {
		String line = in.nextLine();
		comm.append(line);
		comm.append("\n");
	}
}

 

import java.awt.GridBagConstraints;
import java.awt.Insets;

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;
	}
}