Spring Boot学习笔记：JavaMailSender发送邮件

项目中经常会有这样的需求，用户注册成功，需要给用户发送一封邮件。邮件需要有一定格式和样式。本次例子中用freemarker做样式，其他的模版引擎类似。

首先Spring Boot项目，项目结构如下

在pom.xml文件中添加依赖

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-mail</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-freemarker</artifactId>
        </dependency>

配置发件人信息，发件人邮箱需要开通POP3/SMTP服务，如下图（我是采用126邮箱）：

然后在application.properties中添加配置文件：

然后在service层中添加MailService类，代码如下

import freemarker.core.ParseException;
import freemarker.template.MalformedTemplateNameException;
import freemarker.template.Template;
import freemarker.template.TemplateException;
import freemarker.template.TemplateNotFoundException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.mail.SimpleMailMessage;
import org.springframework.mail.javamail.JavaMailSender;
import org.springframework.mail.javamail.MimeMessageHelper;
import org.springframework.stereotype.Service;
import org.springframework.ui.freemarker.FreeMarkerTemplateUtils;
import org.springframework.util.ResourceUtils;
import org.springframework.web.servlet.view.freemarker.FreeMarkerConfig;

import javax.mail.MessagingException;
import javax.mail.internet.MimeMessage;
import java.io.File;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

@Service
public class MailService {

    private final static Logger logger = LoggerFactory.getLogger(MailService.class);

    @Value("${spring.mail.username}")
    private String from;

    @Autowired
    private JavaMailSender mailSender;

    @Autowired
    private FreeMarkerConfig freeMarkerConfig;

    // send simple email
    public String sendSimple(String to, String title, String content) {
        SimpleMailMessage message = new SimpleMailMessage();

        message.setFrom(from);
        message.setTo(to);
        message.setSubject(title);
        message.setText(content);

        mailSender.send(message);

        logger.info("{} send email to {}", from, to);
        return "SUCESS";
    }

    // send template mail
    public String sendTemplateMail(String to, String title) {
        MimeMessage mimeMessage = mailSender.createMimeMessage();
        MimeMessageHelper helper;
        try {
            helper = new MimeMessageHelper(mimeMessage, true);

            helper.setFrom(from);
            helper.setTo(to);
            helper.setSubject(title);

            Map<String, Object> model = new HashMap<>();
            model.put("params", from);
            Template template = freeMarkerConfig.getConfiguration().getTemplate("message.ftl");
            String text = FreeMarkerTemplateUtils.processTemplateIntoString(template, model);

            helper.setText(text, true);

            mailSender.send(mimeMessage);

        } catch (MessagingException e) {
            e.printStackTrace();
        } catch (MalformedTemplateNameException e) {
            e.printStackTrace();
        } catch (ParseException e) {
            e.printStackTrace();
        } catch (TemplateNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (TemplateException e) {
            e.printStackTrace();
        }

        return "SUCEESS";
    }

    // send template mail with attachment
    public String sendAttactmentMail(String to, String title){
        MimeMessage mimeMessage = mailSender.createMimeMessage();
        MimeMessageHelper helper;
        try {
            helper = new MimeMessageHelper(mimeMessage, true);

            helper.setFrom(from);
            helper.setTo(to);
            helper.setSubject(title);

            // add template
            Map<String, Object> model = new HashMap<>();
            model.put("params", from);
            Template template = freeMarkerConfig.getConfiguration().getTemplate("message.ftl");
            String text = FreeMarkerTemplateUtils.processTemplateIntoString(template, model);
            helper.setText(text, true);

            // add attachment
            File file = ResourceUtils.getFile("classpath:static/flcl.jpg");
            helper.addAttachment(file.getName(), file);

            mailSender.send(mimeMessage);

        } catch (MessagingException e) {
            e.printStackTrace();
        } catch (MalformedTemplateNameException e) {
            e.printStackTrace();
        } catch (ParseException e) {
            e.printStackTrace();
        } catch (TemplateNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (TemplateException e) {
            e.printStackTrace();
        }
        return "SUCCESS";
    }
}

这个service中写了三个方法，三个方法的作用分别对应于：发送简单邮件、发送模版邮件、发送带附件的模版邮件

核心方法是 mailSender.send(message) ，message对象根据发送的邮件类型不同而不同，主要有MimeMessage MimeMessageHelper

发送带附件的模板邮件方式是三者中最复杂，首先创建邮件对象MimeMessage ，然后通过MimeMessage对象创建MimeMessageHelper（此对象的作用：向MimeMessage对象中填充数据的助手），通过向MimeMessageHelper对象中添加一些属性，例如发件人、收件人、邮件主题、模版、附件。其中freemarker模板文件xxx.ftl放在resources文件夹下中template（通过FreemakrerConfig获取xxx.ftl的Template对象，然后转换为String），其中附件flcl.jpg放在resources文件夹中的static中（通过ResourceUtils获取文件对象File）。属性添加完成后，就可以发送了。

然后在controller或者其他service层中调用该方法就可以了。

补充：

message.ftl文件内容如下

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Hello</title>
</head>
<body>
<h1>Send email</h1>
<div>this email come from ${params}</div>
</body>
</html> 

发送成功后，可在收件箱中收到邮件