Upload POST file using HttpURLConnection

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Quite often it’s necessary to send/upload a file to a remote server, for example, an image, video, audio or a backup of the application database to a remote private server. Assuming the server is expecting a POST request with the content, here’s a simple example of how to complete this task in Android.

File uploads are sent using multipart/form-data POST requests. It’s very easy to implement:

URL url = new URL(postTarget);
HttpURLConnection connection = (HttpURLConnection) url.openConnection();

String auth = "Bearer " + oauthToken;
connection.setRequestProperty("Authorization", basicAuth);

String boundary = UUID.randomUUID().toString();
connection.setRequestProperty("Content-Type", "multipart/form-data;boundary=" + boundary);

DataOutputStream request = new DataOutputStream(uc.getOutputStream());

request.writeBytes("--" + boundary + "\r\n");
request.writeBytes("Content-Disposition: form-data; name=\"description\"\r\n\r\n");
request.writeBytes(fileDescription + "\r\n");

request.writeBytes("--" + boundary + "\r\n");
request.writeBytes("Content-Disposition: form-data; name=\"file\"; filename=\"" + file.fileName + "\"\r\n\r\n");

request.writeBytes("--" + boundary + "--\r\n");
int respCode = connection.getResponseCode();

switch(respCode) {
    case 200:
        //all went ok - read response
    case 301:
    case 302:
    case 307:
        //handle redirect - for example, re-post to the new location
        //do something sensible

Of course, exceptions will need to be caught or declared as being thrown. A couple points to note about this code:

  1. postTarget is the destination URL of the POST; oauthToken is the authentication token; fileDescription is the description of the file, which is sent as the value of field description; file is the file to be sent - it’s of type java.io.File - if you have the file path, you can use new File(filePath) instead.
  2. It sets Authorization header for an oAuth auth
  3. It uses Apache Common FileUtil to read the file into a byte array - if you already have the content of the file in a byte array or in some other way in memory, then there’s no need to read it.

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