How can i integrate java application with drupal?
This is a very broad question so the answer can only be a broad one...

You can use the Services module to expose resources from your site to interested consumers:


  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.


There's an Example of Java XML-RPC client with Drupal7 and Services 3.x, which (trust me) is the best documentation you'll be able to find.