how to utf-8 encode the file name with uploading the file content in multi part post - file-upload

Question

Having uploading file working fine except when the file name is double byte.
The code snippet below shows a possible place to do the file name encoding, but not sure if it is right, or where is the right place to apply "charset=utf-8". Any help is appreciated.
HttpURLConnection connection = null;
DataOutputStream outputStream = null;
DataInputStream inputStream = null;
String urlString = WebApiConstants.getInstance().getBaseURL();
String lineEnd = "\r\n";
String twoHyphens = "--";
String boundary = "--BoundaryStringUsingCurrentTime”+currentTimeMillis();
int bytesRead, bytesAvailable, bufferSize;
byte[] buffer;
try {
URL url = new URL(urlString);
connection = (HttpURLConnection) url.openConnection();
connection.setDoInput(true);
connection.setDoOutput(true);
connection.setUseCaches(false);
connection.setRequestMethod("POST");
connection.setRequestProperty("Connection", "Keep-Alive");
List<BasicNameValuePair> headers = getHeaderNameValuePairs();
for (BasicNameValuePair hdr : headers) {
connection.setRequestProperty(hdr.getName(), hdr.getValue());
}
connection.setRequestProperty("Content-Type", "multipart/form-data;boundary=" + boundary);
outputStream = new DataOutputStream(connection.getOutputStream());
outputStream.writeBytes(twoHyphens + boundary + lineEnd);
outputStream.writeBytes("Content-Disposition: form-data; name=\"requests\"" + lineEnd);
outputStream.writeBytes("Content-Type: application/json" + lineEnd + lineEnd);
outputStream.writeBytes(getJsonDataString(attachment.getMessageId()));
outputStream.writeBytes(lineEnd + twoHyphens + boundary + lineEnd);
/* ???
// could encode the fail name and put in, not sure if it is right?
String fileNameUtf8 = URLEncoder.encode(fileName, "UTF-8");
outputStream.writeBytes("Content-Disposition: form-data; name=\"file0\";filename=\""
+ fileNameUtf8 + "\"" + lineEnd);
*/
outputStream.writeBytes("Content-Disposition: form-data; name=\"file0\";filename=\""
+ fileName + "\"" + lineEnd);
outputStream.writeBytes("Content-Type: " + mimeType + lineEnd + lineEnd);
FileInputStream fileInputStream = new FileInputStream(new File(pathToFile));
bytesAvailable = fileInputStream.available();
bufferSize = Math.min(bytesAvailable, MAX_BUFFER_SIZE);
buffer = new byte[bufferSize];
bytesRead = fileInputStream.read(buffer, 0, bufferSize);
while (bytesRead > 0) {
outputStream.write(buffer, 0, bufferSize);
bytesAvailable = fileInputStream.available();
bufferSize = Math.min(bytesAvailable, MAX_BUFFER_SIZE);
bytesRead = fileInputStream.read(buffer, 0, bufferSize);
}
outputStream.writeBytes(lineEnd);
outputStream.writeBytes(twoHyphens + boundary + twoHyphens + lineEnd);
… … …
… … …

Answer 1

You can encode the filename like this:
final private static String hexStr = "0123456789ABCDEF";
private static String MimeEncodeQP(String s)
{
byte[] bytes = s.getBytes("UTF-8");
StringBuilder output = new StringBuilder(12 + (bytes.length * 3));
output.append("=?UTF-8?Q?");
for ( final byte b : bytes )
{
if( b == 32 )
{
output.append('_');
}
else if( ((b >= 33) && (b <= 60)) ||
((b >= 62) && (b <= 126)) )
{
output.append((char) b);
}
else
{
output.append('=')
.append(hexStr.charAt((b & 0xF0) >> 4)
.append(hexStr.charAt(b & 0x0F));
}
}
output.append("?=");
return output.toString();
}
outputStream.writeBytes("Content-Disposition: form-data; name=\"file0\";filename=\"" + MimeEncodeQP(fileName) + "\"" + lineEnd);
Read the following specs for more details:
RFC 2045 "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies", Section 67 "Quoted-Printable Content-Transfer-Encoding"
RFC 2047 "MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text"
RFC 7578 "Returning Values from Forms: multipart/form-data", Section 5.1 "Non-ASCII Field Names and Values".
HTML4, Section 17.13.4.2 "multipart/form-data"
HTML5, Section 4.10.22.7 "Multipart form data"