JSP Application - Implicit Objects

In JSP, the application is an implicit object of type ServletContext. It is created once by the web container when the web application is deployed and is shared across all JSP pages. It is mainly used to store and retrieve data that is accessible throughout the entire application.

Available to all JSP pages (application scope)
Helps access initialization parameters from web.xml
Used to share data globally across users

Common Methods of Application Object

setAttribute(String, Object): Stores data in application scope
getAttribute(String): Retrieves stored data
removeAttribute(String): Removes stored attribute
getAttributeNames(): Returns all attribute names
getInitParameter(String): Retrieves initialization parameter from web.xml
getInitParameterNames(): Returns all initialization parameters
getRealPath(String): Converts virtual path to actual system path
log(String): Writes message to server log
getServerInfo(): Returns server information

Step-by-Step Implementation of JSP Application

This section explains the process of creating and configuring JSP files to use the application implicit object for sharing data across the entire application.

Step 1: Create index.html

Create an HTML form to take user input
On submit, data is sent to welcome.jsp

index.html file

HTML

<!DOCTYPE html>
<html>
<head>
<meta charset="ISO-8859-1">
<title>Insert title here</title>
</head>
<body>

<form action="welcome">
<input type="text" name="uname">
<input type="submit" value="go"><br/>
</form>

</body>
</html>

Step 2: Configure web.xml

Define servlet mapping
Add context parameter

web.xml file

XML

<?xml version="1.0" encoding="UTF-8"?>
<web-app>
  <display-name>HelloWorld</display-name>
  
  <servlet>
  <servlet-name>welcome</servlet-name>
  <jsp-file>/welcome.jsp</jsp-file>

  </servlet>
  
  <servlet-mapping>
  <servlet-name>welcome</servlet-name>
  <url-pattern>/welcome</url-pattern>
  </servlet-mapping>
  
  <context-param>
  <param-name>dname</param-name>
  <param-value>com.mysql.jdbc.Driver</param-value>
  </context-param>
  
</web-app>

Step 3: Create welcome.jsp

Retrieve user input using request.getParameter()
Access application data using application.getInitParameter()
Display both values

welcome.jsp

HTML

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="ISO-8859-1">
<title>GeeksforGeeks</title>
</head>
<body>

<%
out.print("Welcome "+request.getParameter("uname"));
String driver=application.getInitParameter("dname");
out.print("<br/>driver name is="+driver);  
%>

</body>
</html>

Output:

Displays user name entered
Displays application-level parameter

Explanation:

User enters name in index.html
Request goes to welcome.jsp
JSP displays user name
Application object retrieves global parameter (driver name)
Output shows both user input and application-level data

Advantages

Data shared across entire application
Reduces duplication of configuration data
Useful for global settings