java 发邮件，怎么设置发信人头像

在 Java 中发送邮件时，可以通过设置邮件头部信息中的 "Content-Type" 和 "Content-Disposition" 字段来添加发件人头像。

示例代码如下：

import java.util.Properties;
import javax.mail.*;
import javax.mail.internet.*;

public class SendEmailWithAvatar {
    public static void main(String[] args) {
        final String username = "your_email@example.com";
        final String password = "your_email_password";

        Properties props = new Properties();
        props.put("mail.smtp.auth", "true");
        props.put("mail.smtp.starttls.enable", "true");
        props.put("mail.smtp.host", "smtp.example.com");
        props.put("mail.smtp.port", "587");

        Session session = Session.getInstance(props, new javax.mail.Authenticator() {
            protected PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication(username, password);
            }
        });

        try {
            Message message = new MimeMessage(session);
            message.setFrom(new InternetAddress("your_email@example.com"));

            // 设置发件人头像
            message.setHeader("Content-Type", "image/jpeg; name=avatar.jpg");
            message.setHeader("Content-Disposition", "inline; filename=avatar.jpg");
            message.setHeader("Content-Transfer-Encoding", "base64");
            message.setContent("<img src='cid:avatar.jpg'/>", "text/html");

            message.setRecipients(Message.RecipientType.TO, InternetAddress.parse("recipient_email@example.com"));
            message.setSubject("Testing Subject");
            message.setText("Dear Mail Crawler," + "\n\n No spam to my email, please!");

            Transport.send(message);

            System.out.println("Done");

        } catch (MessagingException e) {
            throw new RuntimeException(e);
        }
    }
}

在上述代码中，我们设置了邮件头部信息中的 "Content-Type" 和 "Content-Disposition" 字段，将发件人头像作为邮件的内嵌资源，通过 "cid:avatar.jpg" 的方式在邮件正文中引用。