How to call Java server side methods from HTML/JS and android?

The standard way to give access to server-side methods these days is through WebServices.

1. Write your business logic in Java.
2. Add a REST Webservice layer to pass on the requests to the java methods and return the response.
3. REST library will provide the servlet implementation to route your requests - you just need to put a few annotations (Try Jersey REST api)
4. REST library will also convert your java objects into JSON automatically (using some JSON library like Jackson)

Check out this tutorial on REST Webservice: http://www.vogella.com/tutorials/REST/article.html

Webservice is just like a web URL except that it returns JSON text instead of HTML. To call the service, you have to place a normal Ajax request and interpret the response as JSON. I prefer using JQuery to make it easy and cross-browser safe.

1. Call this method to place the ajax request (asynchronous) $.getJSON(url, callbackFn);
2. Define a callback function

3. The function will get called when the response is received

   function callbackFn(responseObj){ alert( JSON.toString( response ) );
   }

Example: http://www.pureexample.com/jquery/get-json.html

The only way I know to direct call java method in distributed systems in Java is using RMI. But this solution is not good for you. First, because I think you only can use RMI when both system (client and server) are Java systems. Second, the Android platform doesn't support rmi by default.

The way people usually solve this is using Web Services. I recommend to you use JSON how transfer format between the client and the server, because how you will have to handle with this in the browser and using json can facilitate your life instead use XML, for example.

More one tip: I also recommend you use GSON library to make the conversion/parse between JSON Files and Java Models. You can have more information here how this works: https://sites.google.com/site/gson/gson-user-guide