Expression Language (EL) in JSP

There are many implicit objects, operators and reserve words in EL.The Expression Language (EL) simplifies the accessibility of data stored in the Java Bean component, and other objects like request, session, application etc.

It is the newly added feature in JSP technology version 2.0.

EL helps you to save your programming time.

Syntax for Expression Language (EL)

1. ${ expression }  

Implicit Objects in Expression Language (EL)

There are many implicit objects in the Expression Language. They are as follows:

Implicit Objects	Usage
pageScope	it maps the given attribute name with the value set in the page scope
requestScope	it maps the given attribute name with the value set in the request scope
sessionScope	it maps the given attribute name with the value set in the session scope
applicationScope	it maps the given attribute name with the value set in the application scope
param	it maps the request parameter to the single value
paramValues	it maps the request parameter to an array of values
header	it maps the request header name to the single value
headerValues	it maps the request header name to an array of values
cookie	it maps the given cookie name to the cookie value
initParam	it maps the initialization parameter
pageContext	it provides access to many objects request, session etc.

Simple example of Expression Language that prints the name of the user

In this example, we have created two files index.jsp and process.jsp. The index.jsp file gets input from the user and sends the request to the process.jsp which in turn prints the name of the user using EL.

index.jsp

1. <form action="process.jsp">  
2. Enter Name:<input type="text" name="name" /><br/><br/>  
3. <input type="submit" value="go"/>  
4. </form>  

process.jsp

1. Welcome, ${ param.name }  

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Example of Expression Language that prints the value set in the session scope

In this example, we printing the data stored in the session scope using EL. For this purpose, we have used sessionScope object.

index.jsp

1. <h3>welcome to index page</h3>  
2. <%  
3. session.setAttribute("user","sonoo");  
4. %>  
5.   
6. <a href="process.jsp">visit</a>  

process.jsp

1. Value is ${ sessionScope.user }  

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JSP Session

This JSP Tutorial shows you how to track the session between different JSP pages. In any web application user moves from one page to another and it becomes necessary to track the user data and objects throughout the application. JSP provide an implicit object "session", which can be use to save the data specific the particular to the user.

In this tutorial we will create an application that takes the user name from the user and then saves into the user session. We will display the saved data to the user in another page.

Here is the code of the JSP file (savenameform.jsp) that takes the input from user:

<%@ page language="java" %> <html> <head> <title>Name Input Form</title> </head> <body> <form method="post" action="savenametosession.jsp"> <p><b>Enter Your Name: </b><input type="text" name="username"><br> <input type="submit" value="Submit"> </form> </body>

 The above page prompts the user to enter his/her name. Once the user clicks on the submit button, savenametosession.jsp is called. The JSP savenametosession.jsp retrieves the user name from request attributes and saves into the user session using the functionsession.setAttribute("username",username);. Here is the code of savenametosession.jsp:

<%@ page language="java" %> <% String username=request.getParameter("username"); if(username==null) username=""; session.setAttribute("username",username); %> <html> <head> <title>Name Saved</title> </head> <body> <p><a href="showsessionvalue.jsp">Next Page to view the session value</a><p> </body>

 The above JSP saves the user name into the session object and displays a link to next pages (showsessionvalue.jsp). When user clicks on the "Next Page to view session value" link, the JSP pageshowsessionvalue.jsp displays the user name to the user. Here is the code of showsessionvalue.jsp:

<%@ page language="java" %> <% String username=(String) session.getAttribute("username");if(username==null) username=""; %> <html> <head> <title>Show Saved Name</title> </head> <body> <p>Welcome: <%=username%><p> </body>

The function session.getAttribute("username") is used to retrieve the user name saved in the session.