HTTP Form POST Request using AJAX and Servlet

In Java World Servlets are popularly used for Model View Controller(MVC) Design Pattern. This article will guide you on writing AJAX based application that will post data to Servlet and will fetching the computed data from the Servlet. With this approach the page will get the updated content from the server without refreshing the jsp/html page.

JSP Code:

<html>
<head>
<title>JSP and Servlet using AJAX</title>
<script type="text/javascript">
 
function getXMLObject()  //XML OBJECT
{
   var xmlHttp = false;
   try {
     xmlHttp = new ActiveXObject("Msxml2.XMLHTTP")  // For Old Microsoft Browsers
   }
   catch (e) {
     try {
       xmlHttp = new ActiveXObject("Microsoft.XMLHTTP")  // For Microsoft IE 6.0+
     }
     catch (e2) {
       xmlHttp = false   // No Browser accepts the XMLHTTP Object then false
     }
   }
   if (!xmlHttp && typeof XMLHttpRequest != 'undefined') {
     xmlHttp = new XMLHttpRequest();        //For Mozilla, Opera Browsers
   }
   return xmlHttp;  // Mandatory Statement returning the ajax object created
}
 
var xmlhttp = new getXMLObject();	//xmlhttp holds the ajax object
 
function ajaxFunction() {
  if(xmlhttp) { 
  	var txtname = document.getElementById("txtname");
    xmlhttp.open("POST","getname",true); //getname will be the servlet name
    xmlhttp.onreadystatechange  = handleServerResponse;
    xmlhttp.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
    xmlhttp.send("txtname=" + txtname.value); //Posting txtname to Servlet
  }
}
 
function handleServerResponse() {
   if (xmlhttp.readyState == 4) {
     if(xmlhttp.status == 200) {
       document.myForm.message.innerHTML=xmlhttp.responseText; //Update the HTML Form element 
     }
     else {
        alert("Error during AJAX call. Please try again");
     }
   }
}
</script>
<body>
<form name="myForm" method="POST" action="getname">
<table>
 <tr>
  <td>Enter Name</td>
  <td><input type="text" name="txtname" id="txtname" /></td>
 </tr>
 <tr>
  <td colspan="2"><input type="button" value="Submit"  onclick="ajaxFunction();" /></td>
 </tr> 
</table>
<div id="message"></div> 
</form>
</body>
</head>
</html>

Servlet Code

import java.io.*;
 
import java.text.*;
 
import java.util.*;
 
import javax.servlet.*;
 
import javax.servlet.http.*;
 
public class getname extends HttpServlet {
 
	public void init(ServletConfig config) throws ServletException {	
		super.init(config);
	}
 
	public void destroy() {
 
	}
 
	public void doPost(HttpServletRequest request,HttpServletResponse response) throws IOException, ServletException {
		String name = null;
		PrintWriter out = response.getWriter();
		if(request.getParameter("txtname") != null) {
			name = request.getParameter("txtname");
		}
                else {
                       name = "";
                }
  	        out.println("You have successfully made Ajax Call:" + name);
	}
}

Explanation for the AJAX Code

Here i have declared 3 JavaScript function:
getXMLObject() – Responsible for creating the AJAX Object depending on the browser.
ajaxFunction() – Responsible for calling servlet through AJAX call.
handleServerResponse() – Responsible for displaying the data retrieved from the server.

How the AJAX Code Works:

When the page loads i am creating an AJAX Object by calling the getXMLObject() function and returning the object created in the xmlhttp variable
When the user clicks on the input Button, ajaxFunction() gets called which checks for whether the Ajax Object is created or not and depending on that calls the remote script. Here a function handler handleServerResponse is also defined for retrieving the value from the server
When the readystate of the AJAX call reaches 4 and the http status is 200 we pass the data fetched from the server to the textbox

Explanation for the Servlet Code

By default doPost function gets called when you post the content to the servlet
In doPost function i am fetching the POST data in the form of txtname and assigning it to the local variable name
Finally i am displaying the data got through POST. All the displayed data gets passed to the Ajax Object in the form of response to the Ajax call made to the servlet

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HTTP Form POST Request using AJAX and Servlet

Explanation for the AJAX Code

Explanation for the Servlet Code

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Techie Zone

HTTP Form POST Request using AJAX and Servlet

Explanation for the AJAX Code

Explanation for the Servlet Code

Popular Articles:

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Categories

Java Tutorial

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