Android REST API post

Question

I'm trying to call rest api from android for the first time. I'm using post method.. this is my code. I'm getting http status code 500. What am I doing wrong.

public void loginUser(View view) {
    EditText user = (EditText) findViewById(R.id.enter_username);
    EditText pass = (EditText) findViewById(R.id.enter_password);
    String username = user.getText().toString();
    String password = pass.getText().toString();
    if (username != null && !username.isEmpty() && password != null && !password.isEmpty()) {
        String urlString = "URL TO BE ENTERED HERE"; //TO DO
        //new CallAPI().execute(urlString);
        new PostLoginData().execute(urlString);
    }

}

private class PostLoginData extends AsyncTask<String, String, String> {

    @Override
    protected String doInBackground(String... params){
        EditText user = (EditText) findViewById(R.id.enter_username);
        EditText pass = (EditText) findViewById(R.id.enter_password);
        String username = user.getText().toString();
        String password = pass.getText().toString();
        String message = null;

        HttpClient httpClient = new DefaultHttpClient();
        HttpPost httpPost = new HttpPost("http://test.gogch.com/gch-restful/login");
        List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(2);
        nameValuePairs.add(new BasicNameValuePair("username",username));
        nameValuePairs.add(new BasicNameValuePair("password",password));
        try {
            httpPost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
        }
        catch (UnsupportedEncodingException e){
            e.printStackTrace();
        }
        try {
            HttpResponse response = httpClient.execute(httpPost);
            int statusCode = response.getStatusLine().getStatusCode();
            Log.d("Http Post Response:" ,Integer.toString(statusCode));
            message = response.toString();
        }
        catch(ClientProtocolException e){
            e.printStackTrace();
        }
        catch (IOException e){
            e.printStackTrace();
        }
        return message;
    }

    protected void onPostExecute(String result){
        Intent intent = new Intent(getApplicationContext(), DisplayMessageActivity.class);
        intent.putExtra(EXTRA_MESSAGE, result);
        startActivity(intent);
    }
}

json

{
message: "The email or password you entered is incorrect."
isExpired: false
status: false
}

What I'm actually trying is to extract the status from json. Please tell me how do I get the response text correctly.