Return JSON Servlet

Return JSON Servlet

If you want to return back data in JSON format from servlet class please follow steps below:

Steps:

Create jsp as below where it uses jQuery to pass data and call to servlet and it returns data in JSON format:

<%@ 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>Insert title here</title>
<script type="text/javascript" src="https://code.jquery.com/jquery-2.1.1.min.js"></script>
<script type="text/javascript">    

    function returnJSONData()
    {
        var processData = 'JSON'; 
          $.ajax({  
            type: "GET",  
            url: "./AjaxServlet",  
            data: "processData="+processData,  
            success: function(result){
                alert("Data type process: "+result.processData
                        +" First Name: "+result.firstName
                        +" Last Name: "+result.lastName)
            },
            error: function (xhr, ajaxOptions, thrownError) {
                alert("Error status code: "+xhr.status);
                alert("Error details: "+ thrownError);
            }
          }); 

    }
        

</script>
</head>
<body>

<input type="Submit" value="JSON data from servlet" 
            onclick="returnJSONData();">

</body>
</html>

Create servlet as below and return JSON data:

package com.javahonk;

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;

/**
 * Servlet implementation class AjaxServlet
 */
public class AjaxServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public AjaxServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request,
     * HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, 
        HttpServletResponse response) 
            throws ServletException, IOException {

        String processData = request
            .getParameter("processData");
        response.setContentType("application/json");
            response.setHeader("Cache-Control", "no-cache");
            Map<String, String> personMap = 
                    new HashMap<String, String>();
            if (null != processData && processData.
                equalsIgnoreCase("JSON")) {
            personMap.put("processData", processData);
                personMap.put("firstName", "Java");
                personMap.put("lastName", "Honk");
        } else {
        for (int i = 0; i < 5; i++) {
            personMap.put("firstName"+i, "Java");
                personMap.put("lastName"+i, "Honk"); 
        }
        }
            
            
            Gson gson = new GsonBuilder().setPrettyPrinting()
                    .create();
            String json = gson.toJson(personMap);
            response.getWriter().write(json);
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, 
     * HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, 
        HttpServletResponse response) 
            throws ServletException, IOException {
        // TODO Auto-generated method stub
    }

}

If you want to see JSON data execute servlet from browser using servlet name you will see below sample JSON data returned from servlet:

Return JSON Servlet

Or deploy this you will see first jsp page below hit button you will see below sample data with java script alert message:

Return JSON Servlet

Return JSON Servlet

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