Is executing an httpclient that contains both a StringEntity and appended query parameters disallowed?

Question

I don't know if executing an httpclient that contains both a StringEntity and appended query parameters is disallowed or if there is something fundamentally wrong with this code/my assumption about what it's doing?

That being so, this is what I think it's supposed to do/what I'm trying to do:

Attach parameters that have been passed to the method to args within the URL. IOW, serNum and siteNum should end up in the URL like:

http://10.0.2.2:28642.api/DeliveryItems/PostArgsAndXMLFileAsStr?serNum=Bla&siteNum=Bla

I have a larger arg that I want to pass within the body of the httppost, though - not within the URL. This (stringifiedXML) I'm trying to stash within a StringEntity.

Here is the entire method for context:

private class PostDeliveryItemTask extends AsyncTask {

@Override
protected String doInBackground(String... params) {
    String result = "";
    String stringifiedXML = params[0];
    String serNum = params[1];
    String siteNum = params[2];

    Uri.Builder builder = new Uri.Builder();
    builder.scheme("http").authority("10.0.2.2:28642").appendPath("api").appendPath("DeliveryItems").appendPath("PostArgsAndXMLFileAsStr").
            appendQueryParameter("serialNum", serNum).appendQueryParameter("siteNum", siteNum);

    String URLToCall = builder.build().toString();
    try {
        StringEntity se = new StringEntity(stringifiedXML);
        HttpClient httpclient = new DefaultHttpClient();
        HttpPost httppost = new HttpPost(URLToCall);
        httppost.setEntity(se);
        HttpResponse response = httpclient.execute(httppost); // <= goes pear-shaped
        result = response.toString();
    } catch (ClientProtocolException e) {
        Log.e("ClientProtocolException", e.toString());
    } catch (UnsupportedEncodingException uex) {
        Log.e("UnsupportedEncodingException", uex.toString());
    } catch (IOException iox) {
        Log.e("IOException", iox.toString());
    }
    if (null != result) return result;

}

All seems to go well stepping through it until I get to this line:

HttpResponse response = httpclient.execute(httppost);

...where the rubber really meets the silicon. At that point - whammo! It dies a quick death, disappearing into the ether like a Baskerville Hound into the fog. Is it because of mixing and matching URL args and StringEntity? Or??? The "setEntity" line doesn't complain, so I kind of doubt that, but...what could be the problem? LogCat gives me no errors - the app simply croaks.

UPDATE

When it "simply croaks," it ends up between these two lines in AsyncTask.class:

public AsyncTask() { /* compiled code */ }

public final android.os.AsyncTask.Status getStatus() { /* compiled code */ }

UPDATE 2

Sartorial Delimiter suggested: "Try using a different HTTP client. Either the built-in HttpURLConnection or some other."

But how?

With this:

HttpClient httpclient = new HttpURLConnection();

I get, "error: HttpURLConnection is abstract; cannot be instantiated"

With this:

HttpURLConnection httpclient = new DefaultHttpClient();

...there is no ".execute()" method available for httpclient; and the same goes for:

HttpURLConnection httpclient = new HttpURLConnection();

...so...???