PHP为Android Dev返回不同的JSON数据

So I'm looking to return a JSON array containing specific data from a PHP page depending on what parameters/values I supply (the information will be used by an Android application). However I'm not convinced this is the best method to do this, for example I could use things like.

page.php?allcategories

page.php?specificcategory=12

page.php?specificpage=55

(I'd probably have about 7 different parameter types in total).

Obviously within the PHP script, I'd just have several conditional statements to test if these parameters exist.

Is there a more robust or simply 'better' method of doing what I'm trying to achieve? As this was my first idea.

Many thanks