【亲测解决】javamail邮件主题支持中文，邮件内容中文乱码

使用 MimeMessageHelper 配置邮件信息，实例化时指定UTF-8编码，如下所示：

JavaMailSenderImpl javaMailSenderImpl = this.createJavaMailSenderImpl();

MimeMessage mimeMessage = javaMailSenderImpl.createMimeMessage();

MimeMessageHelper helper = new MimeMessageHelper(mimeMessage, true, "UTF-8"); // 设置编码为UTF-8

String from = this.emailConfig.getFromName() + " <" + this.emailConfig.getUsername() + ">";

helper.setTo(this.to);
helper.setFrom(new InternetAddress(from));
helper.setSentDate(new Date());
helper.setSubject(this.subject);
helper.setText(this.content, true);
helper.setReplyTo(this.emailConfig.getReplyToEmail());      
helper.addAttachment(attachmentList);
helper.setCc(ccAddressList);