使用Spring邮件
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。
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="[email protected]"/> <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>
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("[email protected]"));
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());
}
}
}
| Note |
| 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。
org.springframework.mail.javamail.MimeMessageHelper是处理JavaMail邮件时比较顺手组件之一。它可以让你摆脱繁复的JavaMail API。 通过使用MimeMessageHelper，创建一个MimeMessage实例将非常容易：
// 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("[email protected]"); helper.setText("Thank you for ordering!"); sender.send(message);
Multipart email允许添加附件和内嵌资源(inline resources)。内嵌资源可能是你在信件中希望使用的图像或样式表，但是又不想把它们作为附件。
下面的例子将展示如何使用MimeMessageHelper来发送一封email，使用一个简单的JPEG图片作为附件：
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("[email protected]");
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);
下面的例子将展示如何使用MimeMessageHelper来发送一封含有内嵌资源的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("[email protected]");
// 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);
| 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。你加入文本和资源的顺序是非常重要的。首先，你加入文本，随后是资源。如果顺序弄反了，它将无法正常运作！ |
在之前的代码示例中，所有邮件的内容都是显式定义的，并通过调用message.setText(..)来设置邮件内容。 这种做法针对简单的情况或在上述的例子中没什么问题，因为在这里只是为了向你展示基础API。
而在你自己的企业级应用程序中, 基于如下的原因，你不会以上述方式创建你的邮件内容：
-
使用Java代码来创建基于HTML的邮件内容不仅容易犯错，同时也是一件单调乏味的事情
-
这样做，你将无法将显示逻辑和业务逻辑很明确的区分开
-
一旦需要修改邮件内容的显式格式和内容，你需要重新编写Java代码，重新编译，重新部署……
一般来说解决这些问题的典型的方式是使用FreeMarker或者Velocity这样的模板语言来定义邮件内容的显式结构。 这样，你的任务就是在你的代码中，只要创建在邮件模板中需要展示的数据，并发送邮件即可。通过使用Spring对FreeMarker和Velocity的支持类， 你的邮件内容将变得简单，这同时也是一个最佳实践。下面是一个使用Velocity来创建邮件内容的例子：
使用Velocity来创建你的邮件模板，你需要把Velocity加入到classpath中。 同时要根据应用的需要为邮件内容创建一个或者多个Velocity模板。下面的Velocity模板是这个例子中所使用的基于HTML的模板。 这只是一个普通的文本，你可以通过各种其他的编辑器来编辑该文本，而无需了解Java方面的知识。
# in the com/foo/package
<html>
<body>
<h3>Hi ${user.userName}, welcome to the Chipping Sodbury On-the-Hill message boards!</h3>
<div>
Your email address is <a href="mailto:${user.emailAddress}">${user.emailAddress}</a>.
</div>
</body>
</html>
下面提供了一些简单的代码与Spring XML配置，它们使用了上述Velocity模板来创建邮件内容并发送邮件。
package com.foo;
import org.apache.velocity.app.VelocityEngine;
import org.springframework.mail.javamail.JavaMailSender;
import org.springframework.mail.javamail.MimeMessageHelper;
import org.springframework.mail.javamail.MimeMessagePreparator;
import org.springframework.ui.velocity.VelocityEngineUtils;
import javax.mail.internet.MimeMessage;
import java.util.HashMap;
import java.util.Map;
public class SimpleRegistrationService implements RegistrationService {
private JavaMailSender mailSender;
private VelocityEngine velocityEngine;
public void setMailSender(JavaMailSender mailSender) {
this.mailSender = mailSender;
}
public void setVelocityEngine(VelocityEngine velocityEngine) {
this.velocityEngine = velocityEngine;
}
public void register(User user) {
// Do the registration logic...
sendConfirmationEmail(user);
}
private void sendConfirmationEmail(final User user) {
MimeMessagePreparator preparator = new MimeMessagePreparator() {
public void prepare(MimeMessage mimeMessage) throws Exception {
MimeMessageHelper message = new MimeMessageHelper(mimeMessage);
message.setTo(user.getEmailAddress());
message.setFrom("[email protected]"); // could be parameterized...
Map model = new HashMap();
model.put("user", user);
String text = VelocityEngineUtils.mergeTemplateIntoString(
velocityEngine, "com/dns/registration-confirmation.vm", model);
message.setText(text, true);
}
};
this.mailSender.send(preparator);
}
}
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">
<bean id="mailSender" class="org.springframework.mail.javamail.JavaMailSenderImpl">
<property name="host" value="mail.csonth.gov.uk"/>
</bean>
<bean id="registrationService" class="com.foo.SimpleRegistrationService">
<property name="mailSender" ref="mailSender"/>
<property name="velocityEngine" ref="velocityEngine"/>
</bean>
<bean id="velocityEngine" class="org.springframework.ui.velocity.VelocityEngineFactoryBean">
<property name="velocityProperties">
<value>
resource.loader=class
class.resource.loader.class=org.apache.velocity.runtime.resource.loader.ClasspathResourceLoader
</value>
</property>
</bean>
</beans>