Spring - Java/J2EE Application Framework 应用框架第 17 章使用Spring邮件抽象层发送Email

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本文介绍Spring框架提供的邮件发送抽象层，包括主要接口MailSender及其实现，并通过实例演示如何使用SimpleMailMessage和JavaMailSender发送邮件。

第 17 章使用Spring邮件抽象层发送Email

17.1. 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，同时负责低层次的代表客户端的资源处理。

17.2. 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和封装了简单邮件的属性如from, to,cc, subject, text的值对象叫做SimpleMailMessage。一个以MailException为root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。请参考JavaDocs来得到关于邮件异常层次的更多的信息。

为了使用JavaMail中的一些特色如MIME类型的消息,Spring也提供了一个MailSender的子接口, 名为org.springframework.mail.javamail.JavaMailSender，同时也提供了一个对JavaMail的MIME类型的消息分块的回调interface，名为org.springframework.mail.javamail.MimeMessagePreparator

MailSender:

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;

}

JavaMailSender:

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;

}

MimeMessagePreparator:

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;

}

17.3. 使用Spring邮件抽象

让我们来假设有一个业务接口名为OrderManager

public interface OrderManager {

    void placeOrder(Order order);
}

同时有一个use case为：需要生成带有订单号的email信息,并向客户发送该订单。为了这个目的我们会使用MailSender和SimpleMailMessage。

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。

这里为OrderManager的一个实现

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 businness calculations....
        //... * Call the collaborators to persist the order

        //Create a threadsafe "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的定义应该是这样的:

<bean id="mailSender"
      class="org.springframework.mail.javamail.JavaMailSenderImpl">
    <property name="host"><value>mail.mycompany.com</value></property>
</bean>

<bean id="mailMessage"
      class="org.springframework.mail.SimpleMailMessage">
    <property name="from"><value>customerservice@mycompany.com</value></property>
    <property name="subject"><value>Your order</value></property>
</bean>

<bean id="orderManager"
      class="com.mycompany.businessapp.support.OrderManagerImpl">
    <property name="mailSender"><ref bean="mailSender"/></property>
    <property name="message"><ref bean="mailMessage"/></property>
</bean>

下面是OrderManager的实现，使用了MimeMessagePreparator回调接口。请注意这里的mailSender属性类型为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 businness 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());            
        }
    }
}

如果你想使用JavaMail MimeMessage以获得全部的能力，只需要你指尖轻触键盘即可使用MimeMessagePreparator。

请注意这部分邮件代码是一个横切关注点，是一个可以重构至一个定制的SpringAOP advice的完美候选者, 这样就可以不费力的应用到目标对象OrderManager上来。关于这一点请看AOP章节。