Email

spring framework提供了工具库用于发送邮件，并且并不依赖具体的底层邮件系统。

org.springframework.mail包是spring邮件系统的root package，用于发送邮件的接口为MailSender。封装邮件属性的对象为SimpleMailMessage，其封装了邮件主要的属性（例如from和to）。

root package也包含了一套checked exception结构，root exception类型为MailException.

org.springframework.mail.javamail.JavaMailSender接口则是添加了专门的JavaMail特性，例如对MIME消息的支持（从MailSender接口继承）。JavaMailSender也提供了一个回调接口org.springframework.mail.javamail.MimeMessagePreparator用于准备Mime信息。

使用示例

MailSender使用和SimpleMailMessage使用

import org.springframework.mail.MailException;
import org.springframework.mail.MailSender;
import org.springframework.mail.SimpleMailMessage;

public class SimpleOrderManager implements OrderManager {

	private MailSender mailSender;
	private SimpleMailMessage templateMessage;

	public void setMailSender(MailSender mailSender) {
		this.mailSender = mailSender;
	}

	public void setTemplateMessage(SimpleMailMessage templateMessage) {
		this.templateMessage = templateMessage;
	}

	public void placeOrder(Order order) {

		// Do the business calculations...

		// Call the collaborators to persist the order...

		// Create a thread safe "copy" of the template message and customize it
		SimpleMailMessage msg = new SimpleMailMessage(this.templateMessage);
		msg.setTo(order.getCustomer().getEmailAddress());
		msg.setText(
			"Dear " + order.getCustomer().getFirstName()
				+ order.getCustomer().getLastName()
				+ ", thank you for placing order. Your order number is "
				+ order.getOrderNumber());
		try {
			this.mailSender.send(msg);
		}
		catch (MailException ex) {
			// simply log it and go on...
			System.err.println(ex.getMessage());
		}
	}

}

使用JavaMailSender和MimeMessagePreparator

如下示例通过MimeMessagePreparator来发送MimeMessage

public class SimpleOrderManager implements OrderManager {

	private JavaMailSender mailSender;

	public void setMailSender(JavaMailSender mailSender) {
		this.mailSender = mailSender;
	}

	public void placeOrder(final Order order) {
		// Do the business calculations...
		// Call the collaborators to persist the order...

		MimeMessagePreparator preparator = new MimeMessagePreparator() {
			public void prepare(MimeMessage mimeMessage) throws Exception {
				mimeMessage.setRecipient(Message.RecipientType.TO,
						new InternetAddress(order.getCustomer().getEmailAddress()));
				mimeMessage.setFrom(new InternetAddress("mail@mycompany.example"));
				mimeMessage.setText("Dear " + order.getCustomer().getFirstName() + " " +
						order.getCustomer().getLastName() + ", thanks for your order. " +
						"Your order number is " + order.getOrderNumber() + ".");
			}
		};

		try {
			this.mailSender.send(preparator);
		}
		catch (MailException ex) {
			// simply log it and go on...
			System.err.println(ex.getMessage());
		}
	}

}

使用MimeMessageHelper

通过使用org.springframework.mail.javamail.MimeMessageHelper，可以避免复杂的JavaMail API，通过其创建MimeMessage十分简单：

// of course you would use DI in any real-world cases
JavaMailSenderImpl sender = new JavaMailSenderImpl();
sender.setHost("mail.host.com");

MimeMessage message = sender.createMimeMessage();
MimeMessageHelper helper = new MimeMessageHelper(message);
helper.setTo("test@host.com");
helper.setText("Thank you for ordering!");

sender.send(message);

发送附件和内联资源

多数邮件消息都允许使用附件和inline resource。inline resource包含图片、样式表等，但是不希望以附件的形式来显示inline resource。

附件

如下实例显示了如何通过MimeMessageHelper来发送带有图片附件的邮件：

JavaMailSenderImpl sender = new JavaMailSenderImpl();
sender.setHost("mail.host.com");

MimeMessage message = sender.createMimeMessage();

// use the true flag to indicate you need a multipart message
MimeMessageHelper helper = new MimeMessageHelper(message, true);
helper.setTo("test@host.com");

helper.setText("Check out this image!");

// let's attach the infamous windows Sample file (this time copied to c:/)
FileSystemResource file = new FileSystemResource(new File("c:/Sample.jpg"));
helper.addAttachment("CoolImage.jpg", file);

sender.send(message);

inline resource

如下示例显示了如何通过MimeMessageHelper来发送带有inline resource的邮件：

JavaMailSenderImpl sender = new JavaMailSenderImpl();
sender.setHost("mail.host.com");

MimeMessage message = sender.createMimeMessage();

// use the true flag to indicate you need a multipart message
MimeMessageHelper helper = new MimeMessageHelper(message, true);
helper.setTo("test@host.com");

// use the true flag to indicate the text included is HTML
helper.setText("<html><body><img src='cid:identifier1234'></body></html>", true);

// let's include the infamous windows Sample file (this time copied to c:/)
FileSystemResource res = new FileSystemResource(new File("c:/Sample.jpg"));
helper.addInline("identifier1234", res);

sender.send(message);

Spring Boot集成

如果java.mail.host和相应的库（spring-boot-starter-mail)存在，一个默认的JavaMailSender将会被自动创建（如果JavaMailSender不存在自己创建的bean对象）。

某些timeout值默认情况下是无限的，应该手动为其指定值，避免在邮件服务器未响应时线程被阻塞：

spring.mail.properties[mail.smtp.connectiontimeout]=5000
spring.mail.properties[mail.smtp.timeout]=3000
spring.mail.properties[mail.smtp.writetimeout]=5000

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