如何将Microsoft Graph获取的Attachment转换为byte[]（Spring Boot）

方案1：直接从FileAttachment获取字节数组 #

绝大多数普通附件都属于FileAttachment类型，直接强转后就能拿到内置的字节数组属性，这是最简便的方式：

Attachment attachment = _userClient.me().messages(listIdMessage.get(i)).attachments(idAttachment)
        .buildRequest()
        .get();

// 强转为FileAttachment类型
if (attachment instanceof FileAttachment fileAttachment) {
    byte[] fileBytes = fileAttachment.getContentBytes();
    
    // 示例：将字节数组写入文件
    try (OutputStream outputStream = new FileOutputStream("path/file/" + fileAttachment.getName())) {
        outputStream.write(fileBytes);
    } catch (IOException e) {
        e.printStackTrace();
    }
}

方案2：通过content()接口获取输入流转byte[] #

如果需要处理特殊类型附件，或者必须通过流的方式获取内容，修正代码语法并手动将输入流转为字节数组：

try {
    // 获取附件内容输入流
    InputStream inputStream = _userClient.me().messages(listIdMessage.get(i)).attachments(idAttachment)
            .content()
            .buildRequest()
            .get();
    
    // 将InputStream转换为byte[]
    byte[] fileBytes;
    try (ByteArrayOutputStream byteOutStream = new ByteArrayOutputStream()) {
        byte[] buffer = new byte[1024];
        int readLength;
        while ((readLength = inputStream.read(buffer)) != -1) {
            byteOutStream.write(buffer, 0, readLength);
        }
        fileBytes = byteOutStream.toByteArray();
    } finally {
        inputStream.close();
    }
    
    // 示例：写入文件
    try (OutputStream fileOutStream = new FileOutputStream("path/file/" + attachment.getName())) {
        fileOutStream.write(fileBytes);
    }
} catch (Exception e) {
    e.printStackTrace();
}

你原来代码的问题说明 #

• 存在语法错误：byte[] fileBytes = attachment.additionalDataManager().这行代码未完成，直接导致编译失败
• 调用content()时如果报错，大概率是权限配置问题，需确保你的Microsoft Graph应用已申请Mail.Read权限

内容的提问来源于stack exchange，提问作者Juan Moreno