避免在磁盘上创建pdf文件，将其作为java的附件通过电子邮件发送

import com.itextpdf.text.Document;
import com.itextpdf.text.Paragraph;
import com.itextpdf.text.pdf.PdfWriter;
import javax.mail.*;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;
import javax.activation.DataHandler;
import javax.activation.DataSource;
import javax.activation.FileDataSource;
import java.io.FileOutputStream;
import java.util.Properties;

public class EmailWithAttachmentExample {
    public static void main(String[] args) {
        // 生成PDF文件
        createPDF();

        // 发送电子邮件
        sendEmailWithAttachment();
    }

    private static void createPDF() {
        Document document = new Document();

        try {
            PdfWriter.getInstance(document, new FileOutputStream("example.pdf"));
            document.open();
            document.add(new Paragraph("This is an example PDF document."));
            document.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private static void sendEmailWithAttachment() {
        final String username = "your_email@example.com";
        final String password = "your_password";
        String recipientEmail = "recipient@example.com";

        // 设置邮件服务器属性
        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");

        // 创建会话
        Session session = Session.getInstance(props, new Authenticator() {
            protected PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication(username, password);
            }
        });

        try {
            // 创建邮件消息
            Message message = new MimeMessage(session);
            message.setFrom(new InternetAddress(username));
            message.setRecipients(Message.RecipientType.TO, InternetAddress.parse(recipientEmail));
            message.setSubject("Email with PDF Attachment");

            // 创建邮件内容
            Multipart multipart = new MimeMultipart();
            BodyPart messageBodyPart = new MimeBodyPart();
            messageBodyPart.setText("Please see the attached PDF file.");

            // 将生成的PDF文件作为附件添加到邮件中
            DataSource source = new FileDataSource("example.pdf");
            messageBodyPart.setDataHandler(new DataHandler(source));
            messageBodyPart.setFileName("example.pdf");
            multipart.addBodyPart(messageBodyPart);

            // 设置邮件内容
            message.setContent(multipart);

            // 发送邮件
            Transport.send(message);

            System.out.println("Email with PDF attachment sent successfully.");
        } catch (MessagingException e) {
            e.printStackTrace();
        }
    }
}