用java写一个发送邮件的代码

以下是使用JavaMail库发送邮件的示例代码：

import java.util.Properties;
import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;

public class EmailSender {

    public static void main(String[] args) {

        String host = "smtp.example.com"; // 邮件服务器地址
        String port = "587"; // 端口号
        String username = "your_email@example.com"; // 发件人邮箱账号
        String password = "your_email_password"; // 发件人邮箱密码
        String recipient = "recipient@example.com"; // 收件人邮箱地址

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

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

        try {
            Message message = new MimeMessage(session);
            message.setFrom(new InternetAddress(username));
            message.setRecipients(Message.RecipientType.TO, InternetAddress.parse(recipient));
            message.setSubject("Test Email");
            message.setText("This is a test email sent from Java.");

            Transport.send(message);

            System.out.println("Email sent successfully.");

        } catch (MessagingException e) {
            System.out.println("Failed to send email. Error message: " + e.getMessage());
        }
    }
}

请注意，您需要使用您自己的邮件服务器地址、端口号、发件人邮箱账号和密码，以及收件人邮箱地址。此外，您需要在运行代码之前确保已经下载并导入了JavaMail库。