How to send a file via email without storing it in storage first using spring boot?

I am working on a spring boot application. In my project I am creating a .xlsx file and then i have to send via email using spring boot.

I am able to create the file using apache poi but later to send it via mail as an attachment, i should save the file somewhere in local and then move the file back in while sending it as an attachment.

Is there any way in which I can create a .xlsx file and directly send it via email, without saving it somewhere first?

For mail I am using 'org.springframework.boot:spring-boot-starter-mail'

For .xlsx I am using 'org.apache.poi', name: 'poi', version: '4.1.2' and 'org.apache.poi', name: 'poi-ooxml', version: '4.1.2'.

Source Code

       XSSFWorkbook workbook = new XSSFWorkbook();
List<String> s = Arrays.asList("person","animal");
CellStyle style = workbook.createCellStyle();
style.setWrapText(true);
int n = 1;
String source = s.get(0);
Sheet sheet = workbook.createSheet(source);
for (String i : s) {
if(!source.equalsIgnoreCase(i)) {
sheet = workbook.createSheet(i);
Row header = sheet.createRow(0);
CellStyle headerStyle = workbook.createCellStyle();
XSSFFont font = workbook.createFont();
font.setFontName("Arial");
font.setBold(true);
headerStyle.setFont(font);
Cell headerCell = header.createCell(0);
headerCell.setCellValue("Name");
headerCell.setCellStyle(headerStyle);
headerCell = header.createCell(1);
headerCell.setCellValue("Age");
headerCell.setCellStyle(headerStyle);
source = i;
}
Row row = sheet.createRow(n);
Cell cell = row.createCell(0);
cell.setCellValue("Udhav Mohata");
cell.setCellStyle(style);
cell = row.createCell(1);
cell.setCellValue(22);
cell.setCellStyle(style);
n++;
}
FileOutputStream outputStream = new FileOutputStream(Path_to_the_file);
workbook.write(outputStream);
workbook.close();
sendMail();
}
public void sendMail() throws MessagingException, IOException {
MimeMessage message = mailSender.createMimeMessage();
MimeMessageHelper helper = new MimeMessageHelper(message, true);
helper.setFrom("spidercodie@gmail.com");
helper.setTo("udhavmohata1@gmail.com");
helper.setSubject("Test Mail");
helper.setText("Hello world");
FileSystemResource file = new FileSystemResource(path_to_the_file));
helper.addAttachment("Invoice.xlsx", file);
mailSender.send(message);
}
</details>
# 答案1
**得分**: 5
这是我的建议，基于我提供的链接中的方法，这本质上也是Gagravarr在他的评论中提到的。
（这个方法在我使用Gmail时有效。）
**创建Excel文件**
我使用了您的代码，除了最后一部分。我没有将您的工作簿写入文件系统，而是通过`java.io.ByteArrayOutputStream`将其写入字节数组。
```java
ByteArrayOutputStream bos = new ByteArrayOutputStream();
try {
workbook.write(bos);
} finally {
bos.close();
}
byte[] excelFileAsBytes = bos.toByteArray();

使用我的字节数组作为附件

在我的邮件代码中（几乎与您的代码相同，但我不想意外复制/粘贴您的电子邮件地址），我替换了这些行：

FileSystemResource file = new FileSystemResource(path_to_the_file));
helper.addAttachment("Invoice.xlsx", file);

使用org.springframework.core.io.ByteArrayResource的以下行：

ByteArrayResource resource = new ByteArrayResource(excelFileAsBytes);
helper.addAttachment("Invoice.xlsx", resource);

这样就会得到一封包含Excel文件附件的电子邮件。

ByteArrayOutputStream bos = new ByteArrayOutputStream();
try {
workbook.write(bos);
} finally {
bos.close();
}
byte[] excelFileAsBytes = bos.toByteArray();

FileSystemResource file = new FileSystemResource(path_to_the_file));
helper.addAttachment("Invoice.xlsx", file);

ByteArrayResource resource = new ByteArrayResource(excelFileAsBytes);
helper.addAttachment("Invoice.xlsx", resource);