JavaMail 發送郵件完整實戰：文本/HTML/附件/SSL 全覆蓋

架構設計：三層解耦

1. MailSenderInfo：郵件元數據載體（主機、認證、收發件人、主題、正文、附件）；
2. SimpleMailSender：發送引擎，封裝 Session 創建、MimeMessage 組裝、Transport 發送；
3. MyAuthenticator：認證策略，實現 javax.mail.Authenticator。

核心代碼精要

1. 郵件信息封裝

public class MailSenderInfo {
    private String mailServerHost, mailServerPort = "25";
    private String fromAddress, toAddress, userName, password;
    private boolean validate = false;
    private String subject, content;
    private String[] attachFileNames;

    public Properties getProperties() {
        Properties p = new Properties();
        p.put("mail.smtp.host", mailServerHost);
        p.put("mail.smtp.port", mailServerPort);
        p.put("mail.smtp.auth", validate ? "true" : "false");
        return p;
    }
    // 省略 Getter/Setter
}

2. 發送引擎：文本 + HTML 双模式

public class SimpleMailSender {
    // 文本郵件
    public boolean sendTextMail(MailSenderInfo info) {
        Session session = createSession(info);
        try {
            MimeMessage msg = new MimeMessage(session);
            msg.setFrom(new InternetAddress(info.getFromAddress()));
            msg.setRecipient(Message.RecipientType.TO, new InternetAddress(info.getToAddress()));
            msg.setSubject(info.getSubject());
            msg.setSentDate(new Date());
            msg.setText(info.getContent());
            Transport.send(msg);
            return true;
        } catch (MessagingException e) { e.printStackTrace(); return false; }
    }

    // HTML 郵件
    public static boolean sendHtmlMail(MailSenderInfo info) {
        Session session = createSession(info);
        try {
            MimeMessage msg = new MimeMessage(session);
            msg.setFrom(new InternetAddress(info.getFromAddress()));
            msg.setRecipient(Message.RecipientType.TO, new InternetAddress(info.getToAddress()));
            msg.setSubject(info.getSubject());
            msg.setSentDate(new Date());

            Multipart mp = new MimeMultipart();
            MimeBodyPart htmlPart = new MimeBodyPart();
            htmlPart.setContent(info.getContent(), "text/html; charset=utf-8");
            mp.addBodyPart(htmlPart);
            msg.setContent(mp);
            Transport.send(msg);
            return true;
        } catch (MessagingException e) { e.printStackTrace(); return false; }
    }

    private static Session createSession(MailSenderInfo info) {
        Authenticator auth = info.isValidate() ? new MyAuthenticator(info.getUserName(), info.getPassword()) : null;
        return Session.getDefaultInstance(info.getProperties(), auth);
    }
}

3. 認證器

public class MyAuthenticator extends Authenticator {
    private final String userName, password;
    public MyAuthenticator(String userName, String password) {
        this.userName = userName; this.password = password;
    }
    @Override protected PasswordAuthentication getPasswordAuthentication() {
        return new PasswordAuthentication(userName, password);
    }
}

調用示例

MailSenderInfo info = new MailSenderInfo();
info.setMailServerHost("smtp.163.com");
info.setMailServerPort("465"); // SSL 端口
info.setValidate(true);
info.setUserName("your@163.com");
info.setPassword("auth_code"); // 授權碼，非登錄密碼
info.setFromAddress("your@163.com");
info.setToAddress("target@qq.com");
info.setSubject("測試標題");
info.setContent("<h1 style='color:red'>HTML 內容</h1>");

new SimpleMailSender().sendHtmlMail(info);

避坑指南（血淚總結）

• 新註冊郵箱無法發送：需養號一段時間，或使用成熟賬號；
• SMTP 主機與發件人域名必須一致：用 smtp.163.com 發件人必須是 @163.com；
• 授權碼 ≠ 登錄密碼：開啟 SMTP 服務後獲取專用授權碼；
• SSL/TLS 端口：465 (SSL) / 587 (STARTTLS)，對應配置 mail.smtp.ssl.enable=true 或 mail.smtp.starttls.enable=true；
• 附件發送：在 Multipart 中再添加 MimeBodyPart 並 attachFile()。

將三個類打包為 mail-util.jar，未來專案引入即用，告別重複造輪子。