22.2. 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);
}

我们同时假设有一个用例：需要生成带有订单号的email信件, 并向客户发送该订单。

22.2.1. MailSender 和 SimpleMailMessage 的基本用法

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());            
        }
    }
}

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>

<!-- this is a template message that we can pre-load with default state -->
<bean id="templateMessage" 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.SimpleOrderManager">
  <property name="mailSender" ref="mailSender"/>
  <property name="templateMessage" ref="templateMessage"/>
</bean>

22.2.2. 使用 JavaMailSender 和 MimeMessagePreparator

下面是OrderManager的另一种实现, 使用了MimeMessagePreparator回调接口。 请注意在这个用例中，mailSender属性是JavaMailSender类型， 所以我们可以使用JavaMail的MimeMessage类：

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 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.com"));
                mimeMessage.setText(
                    "Dear " + order.getCustomer().getFirstName() + " "
                        + order.getCustomer().getLastName()
                        + ", thank you for placing 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());            
        }
    }
}

注意

以上的邮件代码是一个横切关注点，能被完美地重构为自定义Spring AOP切面的候选者，这样它就可以在目标对象OrderManager的一些合适的连接点（joinpoint）中被执行了。

Spring Framework的邮件支持直接提供两种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com.oreilly.servlet包中。请查阅相关Javadocs以获得进一步的资料。