AJAX with Servlets using JQuery and JSON



In my previous post, I explained about making AJAX calls to a servlet from a JSP page and updating a part of the JSP page with the response from the Servlet. That was a very simple example I provided in that post by returning a piece of text from the servlet to JSP to start with, and now in this post I am going to add something more to it by making the servlet return complex Java Objects such as lists, maps, etc. To do this, let us get introduced to JSON(Javascript Object Notation), in addition to JQuery and AJAX. JSON is derived from Javascript for representing simple data structures and associative arrays, called objects. Here in our scenario, we are going to use a JSON library in Servlet to convert Java objects (lists,maps,arrays.etc) to JSON strings that will be parsed by JQuery in the JSP page and will be displayed on the web page.


There are many JSON libraries available that can be used to pass AJAX updates between the server and the client. I am going to use google's gson library in this example. 

Now, let us create a simple JSP page with two drop down lists, one that contains values for countries and the other that is going to be populated with values for states based on the value of country selected in the first drop down list. Whenever the value is selected in the "country" drop down list, the "states" drop down list will be populated with corresponding state values based on the country selected. This has to be done without a page refresh, by making AJAX calls to the servlet on the drop down list change event.

Here are the steps to reproduce in Eclipse,

1. First of all create a "Dynamic Web Project" in Eclipse.
2. Create a new JSP page under "Webcontent" folder and copy paste the below code in it.

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>AJAX calls to Servlet using JQuery and JSON</title>
<script src="http://code.jquery.com/jquery-latest.min.js"></script>
<script>
    $(document).ready(function() {
        $('#country').change(function(event) {  
        var $country=$("select#country").val();
           $.get('ActionServlet',{countryname:$country},function(responseJson) {   
          var $select = $('#states');                           
               $select.find('option').remove();                          
               $.each(responseJson, function(key, value) {               
                   $('<option>').val(key).text(value).appendTo($select);      
                    });
            });
        });
    });          
</script>
</head>
<body>
<h1>AJAX calls to Servlet using JQuery and JSON</h1>
Select Country:
<select id="country">
<option>Select Country</option>
<option value="India">India</option>
<option value="US">US</option>
</select>
<br/>
<br/>
Select State:
<select id="states">
<option>Select State</option>
</select>
</body>
</html>


3. Download google's GSON library from here and place it in your project's WEB-INF/lib folder.
4. Create a servlet in the name 'ActionServlet' (since I have used this name in the jquery code above') in the src directory. Copy and paste the below code in the doGet() method of the servlet and add the import statement in the header section of the servlet.


import com.google.gson.Gson;

protected void doGet(HttpServletRequest request,   HttpServletResponse response) throws ServletException, IOException {
String country=request.getParameter("countryname");
Map<String, String> ind = new LinkedHashMap<String, String>();
   ind.put("1", "New delhi");
   ind.put("2", "Tamil Nadu");
   ind.put("3", "Kerala");
   ind.put("4", "Andhra Pradesh");
   
   Map<String, String> us = new LinkedHashMap<String, String>();
   us.put("1", "Washington");
   us.put("2", "California");
   us.put("3", "Florida");
   us.put("4", "New York");
   String json = null ;
   if(country.equals("India")){
    json= new Gson().toJson(ind);   
   }
   else if(country.equals("US")){
    json=new Gson().toJson(us);  
   }
   response.setContentType("application/json");
   response.setCharacterEncoding("UTF-8");
   response.getWriter().write(json);     
}

}


In the above code, we create two maps for two countries, and return the one based on the country parameter passed to the servlet in the AJAX call made by the JQuery's get() method. Here we convert the map objects to json strings in order to send the response back to the JSP page.

5. Make sure you have done servlet mapping properly in web.xml file. An example of this is given below,

<servlet>
    <servlet-name>ActionServlet</servlet-name>
    <servlet-class>ajaxdemo.ActionServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>ActionServlet</servlet-name>
    <url-pattern>/ActionServlet/*</url-pattern>
</servlet-mapping>

In the above code,'ajaxdemo' is the package name in which I have created the servlet. Replace it with your package structure to make the servlet work properly.



Thats it! You are now all set to run the project with Tomcat. When you run this project, the second drop down list will be populated automatically when you change the value in the first drop down list. 

Output Screenshots:

First drop down list changing,


On selecting 'India' in the first drop down list,


On selecting 'US' in the first drop down list,




Please leave your comments and queries about this post in the comment sections in order for me to improve my writing skills and to showcase more useful posts. 



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Post a Comment

  1. Can we use ajax post here.. what are all the changes to be made for that?

    ReplyDelete
  2. @ameshlal: Yes. We can use. But GET method is generally used for receiving data from the server and post for updating date in the server. In this scenario it is most appropriate to use GET method.

    However if you want to use POST method for reasons like security, you just need to replace $.get method with a $.post in the above example.

    Even more simple example that alerts out the response data,

    $.post("ActionServlet", { name: "John", time: "2pm" },
    function(data) {
    alert("Data Loaded: " + data);
    });

    ReplyDelete
    Replies
    1. I tried your example. I can see the "responseJson" value in the index.jsp. But the values are not populated into states drop down box.

      Delete
    2. This example works fine for me. If the values are not populated in the second drop down box, you will have to debug your jquery response script. Please find the working source code for the above example in the below link. Hope this will help you compare and debug your application.

      https://www.dropbox.com/sh/arhvjju8pflnv2n/o6PIHy85GH/JSONAjax/

      Delete
  3. Its ok but i need ajax for more dropdown box ...How can i do it
    for ex cities in those states

    ReplyDelete
  4. Hello Priya,that was a very nice example.I'm trying to build a JSON object containing data that I retrieve from database in my servlet.So,how can I build such JSON object containing multiple arrays that themselves contains multiple key-value pairs.........
    Plz help me out with this one...........

    ReplyDelete
    Replies
    1. Hi,

      You have to create separate json object for each array of data you want to send from your servlet and then form a single json object that is an array of all the other json objects you created before. This single json object that contains an array of json objects has to be returned to the jsp. See Example below,

      Return Multiple JSON Objects from Servlets to JSP
      Server Side

      String json1 = new Gson().toJson(object1);
      String json2 = new Gson().toJson(object2);
      response.setContentType("application/json");
      String bothJson = "["+json1+","+json2+"]"; //Put both objects in an array of 2 elements
      response.getWriter().write(bothJson);

      Client side

      $.get("MyServlet", parameters, function (data){
      var data1=data[0], data2=data[1]; //We get both data1 and data2 from the array
      $("h3#name").text(data1["name"]);
      $("span#level").text(data1["level"]);
      $("span#college").text(data2["college"]);
      $("span#department").text(data2["department"]);
      });

      Delete
    2. Hi Priya,
      I'm trying to input student record (name,city,college)for 3 students using a loop.I've used JSONObject to store each detail.Then I've added that JSONObject to a JSONArray then I've added that array obj to JSONObject.but its displaying the last set of values I enter for all 3 records....

      Code snippet:

      for(i=0;i<3;i++)
      {
      System.out.println("Enter name");
      name = input.readLine();
      System.out.println("Enter city");
      city = input.readLine();
      System.out.println("Enter college");
      college = input.readLine();

      detail.put("name",name);
      detail.put("city",city);
      detail.put("college",college);

      arr.put(i,detail);
      obj.put("student",arr);
      }

      String output = gson_obj.toJson(obj);
      System.out.println("Output: "+output);

      Input:{1,2,3} {4,5,6} {7,8,9}(Suppose)

      Output: {"myHashMap":{"student":{"myArrayList":[{"myHashMap":{"name":"7","college":"9","city":"8"}},{"myHashMap":{"name":"7","college":"9","city":"8"}},{"myHashMap":{"name":"7","college":"9","city":"8"}}]}}}

      Can u plz tell me where am I going wrong..I'm actually trying to build a JSON obj after retrieving data from database. of the form.........
      {students: [student{name,city,college},student{name,city,college},student{name,city,college}]}

      Delete
  5. hai i got some problem ,,,,,
    i rerieve the values but how to display for the textbox ...
    pls help me

    ReplyDelete
  6. Hi Priya,
    Thanks for this example. It is very helpful to me. Do you have same example with mysql database? Would you please upload it

    ReplyDelete
    Replies
    1. Hi Sumit,

      Welcome! Check out my latest post,

      AJAX Fetch Data from Database in JSP and Servlet with JSONArray

      Hope this helps too!

      Thanks,
      Priya

      Delete
    2. Hi Priya,

      Thanks a lot, your latest post AJAX Fetch Data from Database in JSP and Servlet with JSONArray helped me a lot.

      Thanks,
      Sumit

      Delete
  7. hi thx priya, this article help me a lot....

    ReplyDelete
  8. Hi priya ,

    Nice examples,
    I have one question and I am not able to get solution on it
    Here we selecting one country say india and we are getting list of states in india
    now what should I do if I select both INDIA and US together then we should get all states of India and us within that drop down . How to do this.

    I am able to select multiple countries using (multiple="multiple" ) in JSP but not able to get states so how to do this ... Can you pleaase help me on this

    ReplyDelete
    Replies
    1. Hi Dhaval,

      If you want to enable users to select multiple options, then you have to make ajax calls to servlet whenever an option is selected and deselected. Make sure servlet contains appropriate code to handle each option.

      Check this out for a simple example on how to handle multiple select option in jquery,

      http://api.jquery.com/change/

      Hope this helps!

      Thanks,
      Priya

      Delete
  9. Hi Priya,
    maybe your code may be missing of a starting import like:
    import java.util.*;

    Otherwise LinkedHashMap is not recognized

    ReplyDelete
  10. Hi Priya, can you help me with my question that I post in stackoverflow
    http://stackoverflow.com/questions/18527323/ask-different-response-from-servlet-use-ajax-and-jsp

    I've got trouble on the servlet coz I can't access the different block "if-else condition". Can you help me?

    Thanks Priya.

    ReplyDelete
  11. Hi priya,
    this one is good example, and i want to get JsonArray from server which contains no.of states, and after i want to populate into drop down box(into select tag), without iteration(like without using $each). is there any scenario, if there plz tell me how to do.

    Thank u.

    ReplyDelete
  12. and one more thing it is working with Gson object, what about JSONObject,how to use JsonObect to send data to client

    ReplyDelete
  13. thanks a lot, it was high time i updated from using js based ajax calls to jQuery based ones...

    ReplyDelete
  14. thank you for this helpful tutorials. I am trying to send two or more one dimensional arrays from servlet to a JSP, I tried
    json= new Gson().toJson("["+a1+","+a2+"]"); any help in this regard are highly appreciated

    ReplyDelete
  15. Well, I just posted about your other jQuery/AJAX example and how quick and easy it was to set up and understand, and then I find this one.

    Another simple easy to understand and working example of jQuery/AJAX/JSON...
    Although this took about 5 minutes to get working :-)

    Thank you again

    ReplyDelete
    Replies
    1. Thank you so much for your comment. Keep yourself subscribed to ProgrammingFree via email or social networks for more such useful articles.

      Delete
  16. Hi many thanks for the example has helped me a lot.

    I have a question, I have a arraylist in a class that brings me the names of the State but as I can not pass it to map the servlet

    example.

    servlet.

    this is how I bring the arraylist to servlet

           Consultations Consultations userLis = new ();
              In = userLis.Consultapais ArrayList ();
             
              Map Of String ind = new LinkedHashMap ();
                
      for (Country country: in) {
             ind.put (pais.getNombre (), country);
              
              }

    and run it in the combobox

    I above shows this.

    [object Object]

    I would greatly appreciate if you could help.

    Thank you. :rapt: :rapt:

    ReplyDelete
  17. Thanks priya its a very useful tutorial. But i have an problem that i want to populate data from databse onBlur event of a text field. i tried it for select than its worked fine but when i tried with textfield then i faced a problem that how can we pass textfield value to servlet using json.
    plese help.

    ReplyDelete
  18. Can you post a similar tutorial where the drop down list is populated dynamically from servlets JSON. A three tier tutorial will be a great tutorial I think.

    Thanks

    ReplyDelete
  19. can u add one more dependent dropdown list like distict there

    ReplyDelete
  20. I am having issues running this code that u gave in this post..
    I think there is an issue with GSON lib .. from the link that u gave i got 3 executable jar files and placed them WEB-INF/lib but when i run this code nothing happens :disappointed: ie when i click on US/INDIA ther is nothing in the states .. plz help

    ReplyDelete
  21. Hi Priya,
    Thanks for jTable example. Helped me a lot....

    ReplyDelete

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