(4) 发送E-mail
(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;
}
}