电子邮件协议
SMTP是推协议，负责用户代理向邮件服务器或邮件服务器与邮件服务器间发送邮件;POP3、IMAP是拉协议，负责用户代理从邮件服务器读取邮件。
如何写一封邮件
javaMail用Message对象表示一封邮件。Message类是一个抽象类，我们通常使用它的子类MimeMessage表示一封邮件。
MimeMessage构造器接受一个Session对象，Session对象表示一个会话，该对象由Session.getInstance(property)方法生成，property参数是一个Properties对象，我们借用它设置邮件传输的相关信息。
文本邮件
package com.weixia.SMTP;
import java.util.Date;
import java.util.Properties;
import javax.mail.Message;
import javax.mail.Session;
import javax.mail.internet.MimeMessage;
import javax.mail.internet.InternetAddress;
import java.io.FileOutputStream;
public class Message_text {
public static void main(String[] args) throws Exception {
String from = ""; // 发件人
String to = ""; // 收件人
String subject = "This ia a SMTP test mail"; // 主题
String body = "Hello,world!"; // 邮件正文
Properties property = new Properties();
Session session = Session.getInstance(property);
MimeMessage message = new MimeMessage(session);
message.setFrom(new InternetAddress(from));
// Message.RecipientType.TO ：收件人；Message.RecipientType.CC ：抄送人；Message.RecipientType.BCC ：密送人
message.setRecipients(Message.RecipientType.TO, InternetAddress.parse(to));
message.setSentDate(new Date());
message.setSubject(subject,"UTF-8");
message.setText(body,"UTF-8");
message.saveChanges();
message.writeTo(new FileOutputStream("F:\mail.eml"));
}
}
InternetAddress类解析邮件地址，它的构造器接受一个邮箱格式的字符串，放回一个InternetAddress对象；它的parse方法作用相同，但返回InternetAddress[]，可以用来群发。
HTML格式邮件
package com.weixia.SMTP;
import java.util.Date;
import java.util.Properties;
import javax.mail.Message;
import javax.mail.Session;
import javax.mail.internet.MimeMessage;
import javax.mail.internet.InternetAddress;
import java.io.FileOutputStream;
public class MailWithHtml {
public static void main(String[] args) throws Exception {
String from = "";
String to = "";
String subject = "This ia a SMTP test mail";
String body = "<p>Hello,world!</p>";
Properties property = new Properties();
Session session = Session.getInstance(property);
MimeMessage message = new MimeMessage(session);
message.setFrom(new InternetAddress(from));
message.setRecipients(Message.RecipientType.TO, InternetAddress.parse(to));
message.setSentDate(new Date());
message.setSubject(subject,"UTF-8");
message.setContent(body,"text/html;charset=UTF-8");
message.saveChanges();
message.writeTo(new FileOutputStream("F:\mailWithHtml.eml"));
}
}
HTML格式只需改变设置正文的方法，指明MIME类型。
含有图片、附件或其他媒体类型的邮件
这种复杂邮件，我们把图片、附件或其他媒体类型看作是一个BodyPart对象。因为Message对象setContent方法接受Multipart类型参数，所以必须把BodyPart封装为Multipart对象。
封装的方法如下图：
import java.util.Date;
import java.util.Properties;
import javax.mail.Message;
import javax.mail.Session;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;
import javax.mail.internet.MimeMultipart;
import javax.mail.internet.MimeBodyPart;
import javax.activation.DataHandler;
import javax.activation.FileDataSource;
public class MultiMail {
public static void main(String[] args) throws Exception {
String from = "";
String to = "";
Properties property = new Properties();
Session session = Session.getInstance(property);
MimeMessage message = new MimeMessage(session);
message.setFrom(new InternetAddress(from));
message.setRecipients(Message.RecipientType.TO, InternetAddress.parse(to));
message.setSubject("这是我用java发送的一封邮件", "UTF-8");
message.setSentDate(new Date());
// create picture node
MimeBodyPart image = new MimeBodyPart();
FileDataSource file = new FileDataSource("F:\邮件.jpg");
image.setDataHandler(new DataHandler(file));
// 后边引用该ID时，须使用"cid:idName"的形式，例如"<img src='cid:image_id' />"
image.setContentID("image_id");
// create text node
MimeBodyPart text = new MimeBodyPart();
text.setContent("<p>This is a test picture</p><img src='cid:image_id' />","text/html;charset=UTF-8");
MimeMultipart text_image = new MimeMultipart("related");
text_image.addBodyPart(image);
text_image.addBodyPart(text);
// 为了添加附件，将text_image封装为BodyPart对象
MimeBodyPart text_image_node = new MimeBodyPart();
text_image_node.setContent(text_image);
// 创建附件
MimeBodyPart attachment = new MimeBodyPart();
FileDataSource attachmentFile = new FileDataSource("F:\mail.eml");
DataHandler handler = new DataHandler(attachmentFile);
attachment.setDataHandler(handler);
attachment.setFileName(attachmentFile.getName());
MimeMultipart body = new MimeMultipart("mixed");
body.addBodyPart(text_image_node);
body.addBodyPart(attachment);
message.setContent(body);
message.saveChanges();
return message;
}
}
发送邮件
在发送邮件时，我们要设置传输邮件的相关信息，这里我们使用Properties对象来设置Session会话对象。
通过Session对象获取Transport对象，用connect方法连接邮件服务器，然后用sendMessage方法发送邮件。
SSL连接
现在邮件服务提供商通常使用SSL加密连接，设置SSL如下：
String smtpPort = "465";
Properties property = new Properties();
property.setProperty("mail.smtp.socketFactory.class","javax.net.ssl.SSLSocketFactory");
property.setProperty("mail.smtp.socketFactory.fallback","false");
property.setProperty("mail.smtp.socketFactory.port",smtpPort);
完整代码如下：
package com.weixia.SMTP;
import java.util.Date;
import java.util.Properties;
import javax.mail.Message;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;
import javax.mail.internet.MimeMultipart;
import javax.mail.internet.MimeBodyPart;
import javax.activation.DataHandler;
import javax.activation.FileDataSource;
public class SentMultiMail {
public static void main(String[] args) throws Exception {
String emailAccount = "";
String emailPassword = "";
String recipient = "";
String smtpHost = "smtp.sina.com";
String smtpPort = "465";
Properties property = new Properties();
property.setProperty("mail.transport.protocol","smtp");
property.setProperty("mail.smtp.host",smtpHost);
property.setProperty("mail.smtp,port",smtpPort);
property.setProperty("mail.smtp.auth","true");
property.setProperty("mail.smtp.socketFactory.class","javax.net.ssl.SSLSocketFactory");
property.setProperty("mail.smtp.socketFactory.fallback","false");
property.setProperty("mail.smtp.socketFactory.port",smtpPort);
Session session = Session.getInstance(property);
session.setDebug(true);
MimeMessage message = createMail(session, emailAccount, recipient);
Transport transport = session.getTransport();
transport.connect(emailAccount, emailPassword);
transport.sendMessage(message,message.getAllRecipients());
transport.close();
}
public static MimeMessage createMail(Session session, String from, String to) throws Exception {
MimeMessage message = new MimeMessage(session);
message.setFrom(new InternetAddress(from));
message.setRecipients(Message.RecipientType.TO, InternetAddress.parse(to));
message.setSubject("这是我用java发送的一封邮件", "UTF-8");
message.setSentDate(new Date());
// create picture node
MimeBodyPart image = new MimeBodyPart();
FileDataSource file = new FileDataSource("F:\邮件.jpg");
image.setDataHandler(new DataHandler(file));
// 后边引用该ID时，须使用"cid:idName"的形式，例如"<img src='cid:image_id' />"
image.setContentID("image_id");
// create text node
MimeBodyPart text = new MimeBodyPart();
text.setContent("<p>This is a test picture</p><img src='cid:image_id' />","text/html;charset=UTF-8");
MimeMultipart text_image = new MimeMultipart("related");
text_image.addBodyPart(image);
text_image.addBodyPart(text);
// 为了添加附件，将text_image封装为BodyPart对象
MimeBodyPart text_image_node = new MimeBodyPart();
text_image_node.setContent(text_image);
// 创建附件
MimeBodyPart attachment = new MimeBodyPart();
FileDataSource attachmentFile = new FileDataSource("F:\mail.eml");
DataHandler handler = new DataHandler(attachmentFile);
attachment.setDataHandler(handler);
attachment.setFileName(attachmentFile.getName());
MimeMultipart body = new MimeMultipart("mixed");
body.addBodyPart(text_image_node);
body.addBodyPart(attachment);
message.setContent(body);
message.saveChanges();
return message;
}
}