About Drupal interact with Android
Services module is what you are looking for. It supports json data. More about the module:


  A standardized solution of integrating external applications with Drupal. Service callbacks may be used with multiple interfaces like REST, XMLRPC, JSON, JSON-RPC, SOAP, AMF, etc. This allows a Drupal site to provide web services via multiple interfaces while using the same callback code. 


It also has an extensive documentation.