Chapter 22. Spring邮件抽象层

Chapter 22. Spring邮件抽象层

22.1. 简介

Spring提供了一个发送电子邮件的高级抽象层，它向用户屏蔽了底层邮件系统的一些细节，同时代表客户端负责底层的资源处理。

22.2. Spring邮件抽象结构

Spring邮件抽象层的主要包为org.springframework.mail 。它包括了发送电子邮件的主要接口MailSender ，和值对象 SimpleMailMessage ，它封装了简单邮件的属性如from , to ,cc , subject ,text 。 包里还包含一棵以MailException 为根的checked Exception继承树，它们提供了对底层邮件系统异常的高级别抽象。 要获得关于邮件异常层次的更丰富的信息，请参考Javadocs。

为了使用JavaMail 中的一些特色, 比如MIME类型的信件, Spring提供了MailSender 的一个子接口, 即org.springframework.mail.javamail.JavaMailSender 。Spring还提供了一个回调接口org.springframework.mail.javamail.MimeMessagePreparator , 用于准备JavaMail的MIME信件。

public interface MailSender {



    /**

     * Send the given simple mail message.

     * @param simpleMessage message to send

     * @throws MailException in case of message, authentication, or send errors

     */

    public void send(SimpleMailMessage simpleMessage) throws MailException;



    /**

     * Send the given array of simple mail messages in batch.

     * @param simpleMessages messages to send

     * @throws MailException in case of message, authentication, or send errors

     */

    public void send(SimpleMailMessage[] simpleMessages) throws MailException;



}

public interface JavaMailSender extends MailSender {



    /**

     * Create a new JavaMail MimeMessage for the underlying JavaMail Session

     * of this sender. Needs to be called to create MimeMessage instances

     * that can be prepared by the client and passed to send(MimeMessage).

     * @return the new MimeMessage instance

     * @see #send(MimeMessage)

     * @see #send(MimeMessage[])

     */

    public MimeMessage createMimeMessage();



    /**

     * Send the given JavaMail MIME message.

     * The message needs to have been created with createMimeMessage.

     * @param mimeMessage message to send

     * @throws MailException in case of message, authentication, or send errors

     * @see #createMimeMessage

     */

    public void send(MimeMessage mimeMessage) throws MailException;



    /**

     * Send the given array of JavaMail MIME messages in batch.

     * The messages need to have been created with createMimeMessage.

     * @param mimeMessages messages to send

     * @throws MailException in case of message, authentication, or send errors

     * @see #createMimeMessage

     */

    public void send(MimeMessage[] mimeMessages) throws MailException;



    /**

     * Send the JavaMail MIME message prepared by the given MimeMessagePreparator.

     * Alternative way to prepare MimeMessage instances, instead of createMimeMessage

     * and send(MimeMessage) calls. Takes care of proper exception conversion.

     * @param mimeMessagePreparator the preparator to use

     * @throws MailException in case of message, authentication, or send errors

     */

    public void send(MimeMessagePreparator mimeMessagePreparator) throws MailException;



    /**

     * Send the JavaMail MIME messages prepared by the given MimeMessagePreparators.

     * Alternative way to prepare MimeMessage instances, instead of createMimeMessage

     * and send(MimeMessage[]) calls. Takes care of proper exception conversion.

     * @param mimeMessagePreparators the preparator to use

     * @throws MailException in case of message, authentication, or send errors

     */

    public void send(MimeMessagePreparator[] mimeMessagePreparators) throws MailException;



}

public interface MimeMessagePreparator {



    /**

     * Prepare the given new MimeMessage instance.

     * @param mimeMessage the message to prepare

     * @throws MessagingException passing any exceptions thrown by MimeMessage

     * methods through for automatic conversion to the MailException hierarchy

     */

    void prepare(MimeMessage mimeMessage) throws MessagingException;



}

22.3. 使用Spring邮件抽象

假设某个业务接口名为 OrderManager :

public interface OrderManager {



    void placeOrder(Order order);

}

同时有一个用例为：需要生成带有订单号的email信件, 并向客户发送该订单。 为此，我们会使用MailSender 接口和SimpleMailMessage 类。

请注意,通常情况下,我们在业务代码中使用接口而让Spring ioc容器负责组装我们需要的合作者。

以下是OrderManager 的实现:

import org.springframework.mail.MailException;

import org.springframework.mail.MailSender;

import org.springframework.mail.SimpleMailMessage;



public class OrderManagerImpl implements OrderManager {



    private MailSender mailSender;

    private SimpleMailMessage message;



    public void setMailSender(MailSender mailSender) {

        this.mailSender = mailSender;

    }



    public void setMessage(SimpleMailMessage message) {

        this.message = message;

    }



    public void placeOrder(Order order) {



        // Do the business calculations...



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





        //Create a thread safe "sandbox" of the message

        SimpleMailMessage msg = new SimpleMailMessage(this.message);

        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{

            mailSender.send(msg);

        }

        catch(MailException ex) {

            //log it and go on

            System.err.println(ex.getMessage());            

        }

    }

}

上面的代码的bean定义应该是这样的:

<bean id="mailSender" class="org.springframework.mail.javamail.JavaMailSenderImpl">

  <property name="host" value="mail.mycompany.com"/>

</bean>



<bean id="mailMessage" class="org.springframework.mail.SimpleMailMessage">

  <property name="from" value="customerservice@mycompany.com"/>

  <property name="subject" value="Your order"/>

</bean>



<bean id="orderManager" class="com.mycompany.businessapp.support.OrderManagerImpl">

  <property name="mailSender" ref="mailSender"/>

  <property name="message" ref="mailMessage"/>

</bean>

下面是OrderManager 接口的实现，使用了MimeMessagePreparator 回调接口。 请注意这里的mailSender属性的类型为JavaMailSender ,这样做是为了能够使用JavaMail的MimeMessage ：

import javax.mail.Message;

import javax.mail.MessagingException;

import javax.mail.internet.InternetAddress;

import javax.mail.internet.MimeMessage;



import javax.mail.internet.MimeMessage;

import org.springframework.mail.MailException;

import org.springframework.mail.javamail.JavaMailSender;

import org.springframework.mail.javamail.MimeMessagePreparator;



public class OrderManagerImpl 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 MessagingException {

        

                mimeMessage.setRecipient(Message.RecipientType.TO, 

                        new InternetAddress(order.getCustomer().getEmailAddress()));

                mimeMessage.setFrom(new InternetAddress("mail@mycompany.com"));

                mimeMessage.setText(

                    "Dear "

                        + order.getCustomer().getFirstName()

                        + order.getCustomer().getLastName()

                        + ", thank you for placing order. Your order number is "

                        + order.getOrderNumber());

            }

        };

        try {

            mailSender.send(preparator);

        }

        catch (MailException ex) {

            //log it and go on

            System.err.println(ex.getMessage());            

        }

    }

}

如果你想获得JavaMail MimeMessage 的全部能力，你可以使用MimeMessagePreparator 。

	Note
	以上的邮件代码是一个横切关注点，是重构为定制SpringAOP advice的完美候选者,这样就可以在目标对象OrderManager 合适的joinpoint中运行。请参阅Chapter 6, 使用Spring进行面向切面编程（AOP） 章节。

22.3.1. 可插拔的MailSender实现

Spring直接提供两种MailSender 的实现:标准的JavaMail实现,和基于Jason Hunter 编写的MailMessage 类之上的实现,后者位于http://servlets.com/cos (com.oreilly.servlet)。进一步的资料请查阅相关Javadocs。

22.4. 使用 JavaMail MimeMessageHelper

org.springframework.mail.javamail.MimeMessageHelper 是处理JavaMail邮件常用的顺手组件之一。它可以让你摆脱繁复的javax.mail.internet API类。下面是一些通常的场景：

22.4.1. 创建一条简单的MimeMessage ，并且发送出去

使用MimeMessageHelper 来创建和发送 MimeMessage 消息是非常容易的:

// 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);

22.4.2. 发送附件和嵌入式资源(inline resources)

Email允许添加附件，也允许在multipart信件中内嵌资源。内嵌资源可能是你在信件中希望使用的图像，或者样式表，但是又不想把它们作为附件。下面的例子演示如何使用MimeMessageHelper 来发送带有内嵌图像的email。

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);



// if you would need to include the file as an attachment, use

// the various addAttachment() methods on the MimeMessageHelper





sender.send(message);

	Warning
	如你所见，嵌入式资源使用Content-ID(上例中是identifier1234 )来插入到mime信件中去。你加入文本或者资源的顺序是非常重要的。首先，你加入文本，随后是资源。如果你弄反了顺序，它将无法正常运作！

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