基于Freemarker模板技术的邮件发送模块设计

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1.项目背景设计一个通用的邮件发送模块，为上层应用提供服务，对上层屏蔽掉发送邮件的细节，上层只需要简单的调用即可，要求可以实时发送但又不能影响效率，对发送失败的邮件系统可以记录下来，以便后期重发
2.需求分析
关键点有
2.1邮件内容的存放
a)直接把邮件内容写死在代码里，然后拼接成一个很长的字符串，缺点也很明显，要改邮件的内容必修修改代码，重新编译打包
b)邮件内容与代码相分离.将邮件的内容文件化，java代码中只是引用模板的位置，然后解析模块中的内容输出，这种方案有着更高的可维护性，扩展起来也更方便
2.2发送邮件的效率
发邮件是一件很耗费性能的操作，如果系统中会频繁用到邮件发送，邮件发送不要影响正常的业务操作
2.3自动记录错误和重发
邮件发送失败时，出错的邮件要保存起来，以便日后重发
3.关键技术点
3.1.email发送可以通过javamail api实现
3.2邮件内容模板采用的是freemarker技术来实现
3.3异步发送邮件，采用的是java的多线程机制
4.设计细节

4.1整体类图

4.2类描述

EmailServer:邮件服务器，用来进行邮件服务器的配置和实际的邮件发送，这里调用底层的javamail实现，核心方法

send(EmailInfo emailInfo)这个是个邮件发送的模板方法

EmailSendListener:邮件发送器监听程序，一个observer模式的实现，当有邮件要发送时触发，可以为邮件服务器配置一个或多个监听程序，定义了三个核心接口方法

before(EmailContext emailContext)邮件发送前做的操作

after(EmailContext emailContext)邮件发送结束后做的操作

afterThrowable(EmailContext emailContext)邮件发送出现异常时做的处理

EmailTemplateService：邮件的内容采用了模板技术来实现，定义一个统一的顶层接口getText，对于不同的模板技术实现Freemarker或Velocity分别实现该方法

EmailSendFacade:邮件发送模块对外暴露的外部接口，用来封装各个底层实现细节

EmailContext:邮件监听器用到的邮件发送上线文信息，主要有EmailInfo邮件基本信息和Throwable两个字段

4.3系统时序图

4.4项目整体目录结构

4.5核心类源码解读

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package com.crazycoder2010.email;
import java.util.ArrayList;
import java.util.List;
import java.util.Properties;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import javax.mail.Authenticator;
import javax.mail.BodyPart;
import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.Multipart;
import javax.mail.PasswordAuthentication;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.AddressException;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeBodyPart;
import javax.mail.internet.MimeMessage;
import javax.mail.internet.MimeMultipart;
/**
* 郵件服務器
*
* @author Kevin
*
*/
public class EmailServer {
private static final int POOL_SIZE = 5;
private Session session;
private ExecutorService theadPool;
/**
* 郵件監聽器
*/
private List<EmailSendListener> emailSendListeners = new ArrayList<EmailSendListener>();
public void init() {
final Properties properties = SysConfig.getConfiguration();
this.theadPool = Executors.newFixedThreadPool(POOL_SIZE);
this.session = Session.getDefaultInstance(properties,
new Authenticator() {
@Override
protected PasswordAuthentication getPasswordAuthentication() {
return new PasswordAuthentication(properties
.getProperty("mail.smtp.username"), properties
.getProperty("mail.smtp.password"));
}
});
this.session.setDebug(true);//生产环境把其设置为false
}
/**
* 發送單條email
*
* @param emailInfo
*/
public void send(final EmailInfo emailInfo) {
this.theadPool.execute(new Runnable() {
public void run() {
EmailContext emailContext = new EmailContext();
emailContext.setEmailInfo(emailInfo);
doBefore(emailContext);
try {
Message msg = buildEmailMessage(emailInfo);
Transport.send(msg);
doAfter(emailContext);
} catch (Exception e) {
emailContext.setThrowable(e);
doAfterThrowable(emailContext);
}
}
});
}
private Message buildEmailMessage(EmailInfo emailInfo)
throws AddressException, MessagingException {
MimeMessage message = new MimeMessage(this.session);
message.setFrom(convertString2InternetAddress(emailInfo.getFrom()));
message.setRecipients(Message.RecipientType.TO,
converStrings2InternetAddresses(emailInfo.getTo()));
message.setRecipients(Message.RecipientType.CC,
converStrings2InternetAddresses(emailInfo.getCc()));
Multipart multipart = new MimeMultipart();
BodyPart messageBodyPart = new MimeBodyPart();
messageBodyPart.setContent(emailInfo.getContent(), "text/html;charset=UTF-8");
multipart.addBodyPart(messageBodyPart);
message.setContent(multipart);
message.setSubject(emailInfo.getTitle());
message.saveChanges();
return message;
}
private InternetAddress convertString2InternetAddress(String address)
throws AddressException {
return new InternetAddress(address);
}
private InternetAddress[] converStrings2InternetAddresses(String[] addresses)
throws AddressException {
final int len = addresses.length;
InternetAddress[] internetAddresses = new InternetAddress[len];
for (int i = 0; i < len; i++) {
internetAddresses[i] = convertString2InternetAddress(addresses[i]);
}
return internetAddresses;
}
public void addEmailListener(EmailSendListener emailSendListener) {
this.emailSendListeners.add(emailSendListener);
}
/**
* 發送多條email
*
* @param emailInfos
*/
public void send(List<EmailInfo> emailInfos) {
for (EmailInfo emailInfo : emailInfos) {
send(emailInfo);
}
}
private void doBefore(EmailContext emailContext) {
for (EmailSendListener emailSendListener : this.emailSendListeners) {
emailSendListener.before(emailContext);
}
}
private void doAfter(EmailContext emailContext) {
for (EmailSendListener emailSendListener : this.emailSendListeners) {
emailSendListener.after(emailContext);
}
}
private void doAfterThrowable(EmailContext emailContext) {
for (EmailSendListener emailSendListener : this.emailSendListeners) {
emailSendListener.afterThrowable(emailContext);
}
}
}

邮件服务器的配置参数

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mail.transport.protocol=smtp
mail.smtp.port=25
mail.smtp.host=smtp.163.com
mail.smtp.username=chongzi1266
mail.smtp.password=*********
mail.smtp.connectiontimeout=10000
mail.smtp.timeout=10000
mail.smtp.auth=true

EmailServer是一个典型的模板模式和观察者模式的应用，模板send方法中采用java线程池技术ExcecuteService,在初始化时初始大小为5的线程池，以后每次发送邮件都开启一个新的任务来执行，每发送一个邮件都依次执行EmailSendListener的before,after,afterThrowable方法，从来可以灵活扩展邮件发送的处理逻辑，如默认情况下我们可能只是想要跟踪一下邮件的发送过程，在邮件的发送开始，结束和异常出现时打印出一些基本信息(ConsoleEmailSendListener),实际生产环境时，我们希望把发送失败的邮件和失败的原因记录到数据库，以存后期重发用，这个时候我们就可以提供另一个实现类(DatabaseEmailSendListener)来达到这个效果了，而对于我们整个EmailSever不需要做任何改动，从而达到开闭的原则

FreemarkerEmalTemplateService

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package com.crazycoder2010.email;
import java.io.StringWriter;
import java.util.HashMap;
import java.util.Locale;
import java.util.Map;
import freemarker.cache.ClassTemplateLoader;
import freemarker.template.Configuration;
import freemarker.template.Template;
/**
* 基于Freemarker模板技术的邮件模板服务
* @author Administrator
*
*/
public class FreemarkerEmailTemplateService implements EmailTemplateService {
/**
* 邮件模板的存放位置
*/
private static final String TEMPLATE_PATH = "/email/";
/**
* 启动模板缓存
*/
private static final Map<String, Template> TEMPLATE_CACHE = new HashMap<String, Template>();
/**
* 模板文件后缀
*/
private static final String SUFFIX = ".ftl";
/**
* 模板引擎配置
*/
private Configuration configuration;
public void init(){
configuration = new Configuration();
configuration.setTemplateLoader(new ClassTemplateLoader(FreemarkerEmailTemplateService.class, TEMPLATE_PATH));
configuration.setEncoding(Locale.getDefault(), "UTF-8");
configuration.setDateFormat("yyyy-MM-dd HH:mm:ss");
}
public String getText(String templateId, Map<Object, Object> parameters) {
String templateFile = templateId + SUFFIX;
try {
Template template = TEMPLATE_CACHE.get(templateFile);
if(template == null){
template = configuration.getTemplate(templateFile);
TEMPLATE_CACHE.put(templateFile, template);
}
StringWriter stringWriter = new StringWriter();
template.process(parameters, stringWriter);
return stringWriter.toString();
} catch (Exception e) {
throw new RuntimeException(e);
}
}
}

默认的模板技术实现，这里对模板采用了缓存技术，第一次用到模板的时候会去读取文件，以后都共享内存中的实例了

EmailSendFacade

门面模式的应用，封装了EmailServer和EmailTemplateService，对外部封装内部实现细节

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package com.crazycoder2010.email;
/**
* 邮件发送门面类，用于客户端直接调用
* @author Administrator
*
*/
public class EmailSendFacade {
private EmailTemplateService emailTemplateService;
private EmailServer emailServer;
public void setEmailTemplateService(EmailTemplateService emailTemplateService) {
this.emailTemplateService = emailTemplateService;
}
public void setEmailServer(EmailServer emailServer) {
this.emailServer = emailServer;
}
/**
* 发送邮件
* @param emailInfo 邮件参数封装，emailInfo的title和content字段的值将被重置为实际的值
*/
public void send(EmailInfo emailInfo){
String title = emailTemplateService.getText(emailInfo.getTemplateId()+"-title", emailInfo.getParameters());
String content = emailTemplateService.getText(emailInfo.getTemplateId()+"-body", emailInfo.getParameters());
emailInfo.setContent(content);
emailInfo.setTitle(title);
emailServer.send(emailInfo);
}
}

注意这里对邮件模板做了约定，因为邮件模板包括两部分标题和内容，所以对于一个指定的邮件模板templateId=reset_password，其模板分别为reset_password-title.ftl和reset_password-body.ftl，通过这个约定，调用者只需要传递一个template就可以了而程序内部会去分别读取body和title的值

客户端调用(junit)

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package com.crazycoder2010.email;
import org.junit.Test;
public class EmailSendFacadeTest {
@Test
public void testSend() throws InterruptedException {
//启动邮件服务器
EmailServer emailServer = new EmailServer();
emailServer.init();
emailServer.addEmailListener(new ConsoleEmailSendListener());
emailServer.addEmailListener(new DatabaseEmailSendListener());
//启动模板服务
EmailTemplateService emailTemplateService = new FreemarkerEmailTemplateService();
emailTemplateService.init();//模板引擎初始化
//组装邮件发送门面类
EmailSendFacade emailSendFacade = new EmailSendFacade();
emailSendFacade.setEmailServer(emailServer);//注册邮件服务器
emailSendFacade.setEmailTemplateService(emailTemplateService);//注册模板
//测试数据
EmailInfo emailInfo = new EmailInfo();
emailInfo.setFrom("chongzi1266@163.com");
//emailInfo.setTo(new String[]{"to_01@localhost","to_02@localhost"});
//emailInfo.setCc(new String[]{"cc_01@localhost","cc_02@localhost"});
emailInfo.setTo(new String[]{"wangxuzheng@gmail.com","12708826@qq.com"});
emailInfo.setCc(new String[]{"kwang2003@msn.com","wangxuzheng1983@hotmail.com"});
emailInfo.setTemplateId("reset_password");
emailInfo.addParameter("name", "Kevin");
emailInfo.addParameter("newPassword", "123456");
//发送
emailSendFacade.send(emailInfo);
Thread.sleep(10000);
}
}

这个测试程序写了很长的代码，其实大部分都在做一些核心对象的创建和set操作，在真实的生产环境中这些代码都由DI容器(spring,guiice)自动完成
总结：

这个模块的设计参考了junit3.8优秀的设计思想，采用observer+template来实现灵活扩展邮件功能的方式，采用了邮件模板技术来实现邮件发送内容多样化，配置化，多线程的引入提高了系统的执行效率

其他：

项目中统一编码为UTF-8,包括工程(文件编码)，模板编码,邮件内容编码，否则会出现纠结的中文乱码问题
工程源码下载链接

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