以excel附件為例：

先引入依賴：

		<dependency>
			<groupId>org.apache.poi</groupId>
			<artifactId>poi</artifactId>
			<version>3.17</version>
		</dependency>

@Service
public class MailService {
	private final Logger logger = LoggerFactory.getLogger(this.getClass());
	
	private final JavaMailSender sender;
	
	@Value("${spring.mail.username}")
	private String from;

	public MailService(JavaMailSender sender) {
		this.sender = sender;
	}

	/**
	 * 利用helper設定各種郵件傳送相關的資訊
	 */
	private MimeMessageHelper setInfoByHelper(String to, String subject, String content, MimeMessage message)
			throws MessagingException {
		//true表示需要建立一個multipart message
		MimeMessageHelper helper = new MimeMessageHelper(message, true);
		helper.setFrom(from);
		helper.setTo(to);
		helper.setSubject(subject);
		helper.setText(content, true);
		return helper;
	}
	

	/**
	 * 傳送帶附件的郵件
	 * @param to 收件人列表
	 * @param subject 郵件標題
	 * @param content 郵件內容
	 * @param inputStreamSource 附件streamSource，可以這樣獲得：new ByteArrayResource(ByteArrayOutputStream.toByteArray());
	 * @param fileName 附件的檔名
	 */
	public void sendAttachmentsMail(String to, String subject, String content, InputStreamSource inputStreamSource, String fileName){
		MimeMessage message = sender.createMimeMessage();

		try {
			MimeMessageHelper helper = setInfoByHelper(to, subject, content, message);

			helper.addAttachment(fileName, inputStreamSource);

			sender.send(message);
			logger.debug("帶附件的郵件已經發送。");
		} catch (MessagingException e) {
			logger.error("傳送帶附件的郵件時發生異常！", e);
		}
	}
}
 

利用ByteArrayOutputStream把excel檔案輸出到bytes[]中，然後由ByteArrayResource包裝起來傳遞給郵件服務。

	@Test
	public void sendMailWithExcel() throws IOException {
		String[] headers = {"col1","col2","col3"};
		// 宣告一個工作薄
		HSSFWorkbook wb = new HSSFWorkbook();
		// 生成一個表格
		HSSFSheet sheet = wb.createSheet();
		HSSFRow row = sheet.createRow(0);
		for (int i = 0; i < headers.length; i++) {
			HSSFCell cell = row.createCell(i);
			cell.setCellValue(headers[i]);
		}
		int rowIndex = 1;

		for(int j=0; j<3; j++){
			row = sheet.createRow(rowIndex);
			rowIndex++;
			HSSFCell cell1 = row.createCell(0);
			cell1.setCellValue(j);
			cell1 = row.createCell(1);
			cell1.setCellValue(j+1);
			cell1 = row.createCell(2);
			cell1.setCellValue(j+2);
		}
		for (int i = 0; i < headers.length; i++) {
			sheet.autoSizeColumn(i);
		}

		ByteArrayOutputStream os = new ByteArrayOutputStream(1000);
		wb.write(os);
		wb.close();

		InputStreamSource iss = new ByteArrayResource(os.toByteArray());
		os.close();

		mailService.sendAttachmentsMail("
 
[email protected]",
				"attachmentMail subject",
				"I have an attachment",
				iss, "abc1.xlsx");

	}
}