Android发送带附件SMTP邮件时触发File Not Found Exception求助

I've run into this exact issue before—here's what's going wrong and how to fix it:

The Root Cause #

When you use Intent.ACTION_GET_CONTENT to pick a file, the returned Uri is a content URI (e.g., content://com.android.providers.media.documents/document/image%3A1234), not a direct file system path. If you try to use this URI as a file path for your SMTP client, it will throw a FileNotFoundException because that path doesn't exist in the device's file system.

Additionally, on Android 10+ (API 29+), Scoped Storage restricts direct access to file system paths, so even if you tried to convert the content URI to a real path, it might not work for all file types.

The Solution: Use Input Streams Instead of File Paths #

The best approach is to use the ContentResolver to open an input stream directly from the content URI, then pass that stream to your SMTP attachment handler. This avoids needing a file path entirely and works with all content URIs, regardless of the source.

Here's a revised version of your code that implements this fix:

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if (requestCode == RESULT_SUCCESS && resultCode == RESULT_OK && data != null) {
        Uri fileUri = data.getData();
        new Thread(() -> {
            try {
                // Get access to the content resolver
                ContentResolver contentResolver = getContentResolver();
                // Open an input stream from the content URI
                InputStream fileInputStream = contentResolver.openInputStream(fileUri);
                // Fetch the original filename of the attachment
                String attachmentFileName = getAttachmentFileName(contentResolver, fileUri);

                // Configure SMTP properties (fill in your details)
                Properties smtpProps = new Properties();
                smtpProps.put("mail.smtp.host", "your_smtp_host"); // e.g., "smtp.gmail.com"
                smtpProps.put("mail.smtp.port", "587"); // Common TLS port
                smtpProps.put("mail.smtp.auth", "true");
                smtpProps.put("mail.smtp.starttls.enable", "true");

                // Create SMTP session with authentication
                Session session = Session.getInstance(smtpProps, new Authenticator() {
                    @Override
                    protected PasswordAuthentication getPasswordAuthentication() {
                        return new PasswordAuthentication("your_email@example.com", "your_email_password");
                    }
                });

                // Build the email message
                MimeMessage message = new MimeMessage(session);
                message.setFrom(new InternetAddress("your_email@example.com"));
                message.setRecipients(Message.RecipientType.TO, InternetAddress.parse("recipient@example.com"));
                message.setSubject("Email with Attachment");

                // Create the main message body
                MimeBodyPart messageBody = new MimeBodyPart();
                messageBody.setText("Attached is the file you selected.");

                // Create the attachment part using the input stream
                MimeBodyPart attachmentBody = new MimeBodyPart();
                // Use ByteArrayDataSource to wrap the input stream with the correct MIME type
                attachmentBody.setDataHandler(new DataHandler(
                    new ByteArrayDataSource(fileInputStream, contentResolver.getType(fileUri))
                ));
                attachmentBody.setFileName(attachmentFileName);

                // Combine body and attachment into a multipart message
                Multipart multipart = new MimeMultipart();
                multipart.addBodyPart(messageBody);
                multipart.addBodyPart(attachmentBody);

                message.setContent(multipart);

                // Send the email
                Transport.send(message);
                fileInputStream.close(); // Don't forget to close the stream!

                // Update UI on the main thread
                runOnUiThread(() -> 
                    Toast.makeText(getApplicationContext(), "Email sent successfully!", Toast.LENGTH_SHORT).show()
                );

            } catch (Exception e) {
                e.printStackTrace();
                runOnUiThread(() -> 
                    Toast.makeText(getApplicationContext(), "Error sending email: " + e.getMessage(), Toast.LENGTH_LONG).show()
                );
            }
        }).start();
    }
}

// Helper method to get the filename from a content URI
private String getAttachmentFileName(ContentResolver resolver, Uri uri) {
    String fileName = "attachment";
    Cursor cursor = resolver.query(uri, new String[]{OpenableColumns.DISPLAY_NAME}, null, null, null);
    if (cursor != null && cursor.moveToFirst()) {
        int nameColumnIndex = cursor.getColumnIndex(OpenableColumns.DISPLAY_NAME);
        if (nameColumnIndex != -1) {
            fileName = cursor.getString(nameColumnIndex);
        }
        cursor.close();
    }
    return fileName;
}

Key Notes #

• Permission Check: Make sure you have the INTERNET permission declared in your AndroidManifest.xml:

  <uses-permission android:name="android.permission.INTERNET" />
  

  You don't need storage permissions here because ACTION_GET_CONTENT grants temporary access to the selected file via the content URI.
• Background Execution: Always run SMTP operations in a background thread (as shown in the example) to avoid blocking the main thread and causing ANRs.
• MIME Types: Using contentResolver.getType(fileUri) ensures the attachment uses the correct MIME type, which helps email clients render the attachment properly.

内容的提问来源于stack exchange，提问作者Muhammad Huzaifa