Ajax Cascading DropDownList in JSP & Servlet using JQuery and JSON

 

 
There are times in a web application where you want to populate a dropdown list based on the value of another drop down list. In this example, we will be creating a dropdown list for favorite spots and favorite player; since this scenario involves in returning complex java objects like lists, maps, etc, so I’m using JSON for this purpose.

In the article on AJAX in Servlet & jsp using JQuery I have demonstrated on returning simple object from servlet to jsp via jquery.

Library required

 
Google gson
 

Project Structure

Steps done to set up our Servlet for JSON

 
From the browser perspective: jQuery

jQuery allows you to fire an ajax request via get or post method and expects a JSON object as a response, as described in my previous post the first and second parameter of these method are the url and a key-value pair and the third argument of get method is a function that defines what is to be done with the response that is got back from the Servlet.
 

Recommended reading:

Jsp Page

AJAX in Servlet using JQuery and JSON
	Select Favorite Sports:
	
		Select Sports
		Football
		Cricket
	
	
 

	Select Favorite Player:
	
		Select Player
	

 
Here jquery will fire an ajax request when the value of the first dropdown is changed(id=”sports”).
 

Another must read:

• AJAX Tooltip in Java Web Application using qTip2 jQuery plugin
• jQuery form validation using jQuery Validation plugin
• Pagination in Servlet and JSP using jQuery jTable plugin

 
From the server’s perspective: Servlet

In Servlet, I’m going to use a GSON library to convert Java objects (lists, maps etc) to JSON strings that will be parsed by JQuery in the JSP page and will be displayed on the web page and note that I have returned the response back to jsp based on the value of sports parameter which i pass to the servlet via jQuery’s get() method.
 

Servlet

package com.action;

import java.io.IOException;
import java.util.*;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.google.gson.Gson;

public class JsonServlet extends HttpServlet {

	private static final long serialVersionUID = 1L;

	protected void doGet(HttpServletRequest request,
		HttpServletResponse response) throws ServletException, IOException {

		String sportsName = request.getParameter("sportsName");
		List list = new ArrayList();
		String json = null;

		if (sportsName.equals("Football")) {
			list.add("Lionel Messi");
			list.add("Cristiano Ronaldo");
			list.add("David Beckham");
			list.add("Diego Maradona");
		} else if (sportsName.equals("Cricket")) {
			list.add("Sourav Ganguly");
			list.add("Sachin Tendulkar");
			list.add("Lance Klusener");
			list.add("Michael Bevan");
		} else if (sportsName.equals("Select Sports")) {
			list.add("Select Player");
		}

		json = new Gson().toJson(list);
		response.setContentType("application/json");
		response.getWriter().write(json);
	}
}

Web.xml

Servlet mapping should be done in web.xml as shown below
 

   index.jsp


   JsonServlet
   com.action.JsonServlet


   JsonServlet
   /JsonServlet/*

Demo

 
On selecting ‘Football’ in the first dropdown list
 

 
On selecting ‘Cricket’ in the first dropdown list
 

Other Ajax tutorial from our Blog

• AJAX implementation in Servlets using JQuery and JSON
• AngularJS Interacting with Java Servlet using JSON
• Refresh DIV Content Without Reloading Page using jQuery

Reference