Java - How to send form-data or www-form-urlencoded data over an HttpUrlConnection

Question

I am attempting to use a REST API that only supports passing JSON data through the form-data or www-form-urlencoded attributes. So, my question is, how do I use an HttpUrlConnection to attach multiple form data items? When I use the API through the browser the request looks like this in Chrome:

Form Data
adds:
updates: [{"attributes":{"OBJECTID":2241,"OTHER_FIELD":"500"}}]
deletes:
gdbVersion:
rollbackOnFailure:
f: pjson

But I can't figure out how to replicate this in Java.

This is what I've tried so far:

    HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
    urlConnection.setUseCaches(false);
    urlConnection.setDoOutput(true);
    urlConnection.setRequestMethod("POST");
    urlConnection.addRequestProperty("f", "json");
    urlConnection.addRequestProperty("adds", null);
    urlConnection.addRequestProperty("updates", "[{\"attributes\":{\"OBJECTID\":2241,\"OTHER_FIELD\":\"500\"}}]");
    urlConnection.addRequestProperty("deletes", null);
    urlConnection.addRequestProperty("rollbackOnFailure", "true");
    urlConnection.addRequestProperty("gdbVersion", null);

But it doesn't attach the data as it should...

To those interested I am trying to connect to an ArcGIS feature service API so that I can add, update, or delete features but here I am using ApplyEdits

Answer 1

So I figured out how to solve this and here is the solution:

HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
urlConnection.setDoOutput(true);
urlConnection.setRequestMethod("POST");

First set the request to be a POST request and that there will be some output

StringBuilder encodedUrl = new StringBuilder("adds=" + URLEncoder.encode("[{\"attributes\":{\"OBJECTID\":2241,\"MAXIMOID_PRE\":\"HYD\"}}]", "UTF-8"));
encodedUrl.append("&updates=" + URLEncoder.encode("", "UTF-8"));
encodedUrl.append("&deletes=" + URLEncoder.encode("", "UTF-8"));
encodedUrl.append("&f=" + URLEncoder.encode("json", "UTF-8"));
encodedUrl.append("&rollbackOnFailure=" + URLEncoder.encode("true", "UTF-8"));
encodedUrl.append("&gdbVersion=" + URLEncoder.encode("", "UTF-8"));

This is how each of the form-data values gets set. Each key value is just a java string and then the value is encoded using the URLEncoder.encode. Using this string that has all of the form-data elements we then write it to the outputstream:

final BufferedWriter bfw = new BufferedWriter(new OutputStreamWriter(urlConnection.getOutputStream()));
bfw.write(encodedUrl);
bfw.flush();
bfw.close();

Then after that the response can be received and parsed out.