Use a Servlet to handle AJAX requests?

Question

Basically a yes or no question but I am also looking for advice on best practices for implementation.

Let me know when/if I start to go wrong.

• I have a specific Servlet (AjaxServlet?) that will handle all AJAX requests
• AjaxServlet maps to /ajax/* so all request URLs like /ajax/getDataFromServer will be handled by it
• My doGet overide function is a long if/elseif chain checking the request.getPathInfo() each time
• Each if block in doGet handles a specific url call (/ajax/getDataFromServer)

I want to return JSON and so far I have been building these strings myself. Is there a lightweight JSON package I could use. I know I could for example extend ArrayList (ArrayListJson?) and add a toJson() method and then cast any ArrayList to ArrayListJson but I'm sure this has been done already.

Answer 1

Your basic idea sounds OK, but it would be best to have multiple classes that each handle their own task. A method I have used successfully is to use a single servlet to intercept the call, then pass the task to some other class that actually does the implementation. For example, you could create an interface (named, say, AJAXHandler) that has a method public String performTask(HttpServletRequest request) and use the Factory Pattern in your servlet to instantiate the appropriate class (that implements AJAXHandler) and let that class do its work. The results from the performTask method (the JSON string) is then sent out. When you need a new AJAX call implemented, you just add the new class that implements AJAXHandler and update the Factory with with the new class info.

For JSON handling, I suggest you take a look at json-simple, at http://code.google.com/p/json-simple/

The Factory pattern is described at http://www.oodesign.com/factory-pattern.html

Good Luck!!!

Answer 2

I would say go for REST instead of the long if/else if chain on the servlet also that gives you more control to assemble services to be used.

Answer 3

If you are looking for a lightweight solution to replace your big IF block, you could use reflection to call methods on an object based on request parameters.
as for json for java:http://json.org/java/