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封装邮件发送器类
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在cn.tedu.springmail包中创建邮件实体类：

// 邮件实体类
public class Mail {
    private String       host;        // SMTP服务器地址
    private int          port;        // SMTP服务器端口
    private boolean      auth;        // 是否需要身份认证
    private String       username;    // 用户名
    private String       password;    // 密码(第三方授权码)
    private String       from;        // 发件人
    private List<String> recipients;  // 收件人
    private Date         date;        // 时间
    private String       subject;     // 主题
    private String       text;        // 正文
    private List<String> attachments; // 附件

    public Mail(String host, int port,
                boolean auth, String username, String password,
                String from, List<String> recipients, Date date,
                String subject, String text) {
        this.host = host;
        this.port = port;
        this.auth = auth;
        this.username = username;
        this.password = password;
        this.from = from;
        this.recipients = recipients;
        this.date = date;
        this.subject = subject;
        this.text = text;
    }

    public Mail(String host, int port,
                boolean auth, String username, String password,
                String from, List<String> recipients, Date date,
                String subject, String text, List<String> attachments) {
        this.host = host;
        this.port = port;
        this.auth = auth;
        this.username = username;
        this.password = password;
        this.from = from;
        this.recipients = recipients;
        this.date = date;
        this.subject = subject;
        this.text = text;
        this.attachments = attachments;
    }

    public String getHost() {
        return host;
    }

    public void setHost(String host) {
        this.host = host;
    }

    public int getPort() {
        return port;
    }

    public void setPort(int port) {
        this.port = port;
    }

    public boolean isAuth() {
        return auth;
    }

    public void setAuth(boolean auth) {
        this.auth = auth;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public String getFrom() {
        return from;
    }

    public void setFrom(String from) {
        this.from = from;
    }

    public List<String> getRecipients() {
        return recipients;
    }

    public void setRecipients(List<String> recipients) {
        this.recipients = recipients;
    }

    public Date getDate() {
        return date;
    }

    public void setDate(Date date) {
        this.date = date;
    }

    public String getSubject() {
        return subject;
    }

    public void setSubject(String subject) {
        this.subject = subject;
    }

    public String getText() {
        return text;
    }

    public void setText(String text) {
        this.text = text;
    }

    public List<String> getAttachments() {
        return attachments;
    }

    public void setAttachments(List<String> attachments) {
        this.attachments = attachments;
    }
}

在cn.tedu.springmail包中创建邮件发送器类：

// 邮件发送器类
public class MailSender {
    private Mail mail; // 邮件实体

    public MailSender(Mail mail) {
        this.mail = mail;
    }

    // 发送邮件
    public void send() {
        // 创建包含邮箱服务器配置的属性对象
        Properties properties = new Properties();
        properties.put("mail.smtp.host", mail.getHost()); // SMTP服务器地址
        properties.put("mail.smtp.port", mail.getPort()); // SMTP服务器端口
        properties.put("mail.smtp.auth", mail.isAuth()); // 是否需要身份认证

        // 创建包含属性对象的会话对象
        Session session = Session.getInstance(
            properties, new Authenticator() {
                @Override
                protected PasswordAuthentication getPasswordAuthentication() {
                    return new PasswordAuthentication(
                        mail.getUsername(), mail.getPassword());
                }
            });
        session.setDebug(true);

        try {
            // 创建包含邮件内容的邮件对象
            Message message = createMessage(session);
            // 发送邮件
            Transport.send(message);
        }
        catch (MessagingException |
            UnsupportedEncodingException exception) {
            exception.printStackTrace();
        }
    }

    // 创建包含邮件内容的邮件对象
    private Message createMessage(Session session)
        throws MessagingException, UnsupportedEncodingException {
        // 创建邮件对象
        MimeMessage message = new MimeMessage(session);
        message.setFrom(mail.getFrom()); // 发件人
        if (mail.getRecipients() != null) {
            Address[] recipients = new Address[
                mail.getRecipients().size()];
            for (int i = 0; i < mail.getRecipients().size(); ++i)
                recipients[i] = new InternetAddress(
                    mail.getRecipients().get(i));
            message.setRecipients(RecipientType.TO, recipients); // 收件人
        }
        message.setSentDate(mail.getDate()); // 时间
        message.setSubject(mail.getSubject()); // 主题

        MimeMultipart mp = new MimeMultipart(); // 容器

        MimeBodyPart text = new MimeBodyPart(); // 正文
        text.setContent(mail.getText(), "text/html;charset=utf-8");
        mp.addBodyPart(text); // 将正文加入容器

        if (mail.getAttachments() != null)
            for (String filepath : mail.getAttachments()) {
                File file = new File(filepath);
                if (file.exists()) {
                    MimeBodyPart attachment = new MimeBodyPart(); // 附件
                    DataSource ds = new FileDataSource(file);
                    DataHandler dh = new DataHandler(ds);
                    attachment.setDataHandler(dh);
                    attachment.setFileName(
                        MimeUtility.encodeText(dh.getName()));
                    mp.addBodyPart(attachment); // 将附件加入容器
                    mp.setSubType("mixed"); // 含附件的邮件为混合类型
                }
            }

        message.setContent(mp); // 内容

        // 返回邮件对象
        return message;
    }
}

在cn.tedu.springmail包中创建邮件发送器测试类：

// 邮件发送器测试类
public class MailSenderTest {
    // 测试：发送普通文本邮件
    @Test
    public void testSendPlainTextMail() {
        List<String> recipients = new ArrayList<>();
        recipients.add("johnmin740523@163.com");
        recipients.add("johnmin74@hotmail.com");

        Mail mail = new Mail(
            "smtp.163.com", 25,
            true, "johnmin740523", "QRPYPLKSXOCPPBBN",
            "johnmin740523@163.com", recipients, new Date(),
            "普通文本邮件", "这是一封普通文本邮件");

        MailSender mailSender = new MailSender(mail);
        mailSender.send();
    }

    // 测试：发送HTML格式邮件
    @Test
    public void testSendHTMLMail() {
        List<String> recipients = new ArrayList<>();
        recipients.add("johnmin740523@163.com");
        recipients.add("johnmin74@hotmail.com");

        Mail mail = new Mail(
            "smtp.163.com", 25,
            true, "johnmin740523", "QRPYPLKSXOCPPBBN",
            "johnmin740523@163.com", recipients, new Date(),
            "HTML格式邮件", "<html><body><a href='https://www.baidu.com'>" +
            "这是一封HTML格式邮件</a></body></html>");

        MailSender mailSender = new MailSender(mail);
        mailSender.send();
    }

    // 测试：发送带附件的邮件
    @Test
    public void testSendAttachmentsMail() {
        List<String> recipients = new ArrayList<>();
        recipients.add("johnmin740523@163.com");
        recipients.add("johnmin74@hotmail.com");

        List<String> attachments = new ArrayList<>();
        attachments.add(
            "C:\\Users\\Administrator\\Work\\34_研发课时\\肖旭伟_研发统计表.xlsx");
        attachments.add(
            "C:\\Users\\Administrator\\Work\\31_智库\\photo.jpg");

        Mail mail = new Mail(
            "smtp.163.com", 25,
            true, "johnmin740523", "QRPYPLKSXOCPPBBN",
            "johnmin740523@163.com", recipients, new Date(),
            "带附件的邮件", "这是一封带附件的邮件", attachments);

        MailSender mailSender = new MailSender(mail);
        mailSender.send();
    }
}

运行，登录所有收件邮箱查看。