Expression Language Implicit Variables

Tutorials

Jsp

Topic

How are Implicit Variables used in JSP?

Explanation

Implicit variables are those which are instantiated automatically and are references to objects created by the JSP EL language. These are provided by default by the JSP container.

Following are the list of implicit objects provided by JSP.

Variables	Description
pageScope	Collection of all page scope variables
requestScope	Collection of all request scope variables
sessionScope	Collection of all session scope variables
applicationScope	Collection of all application scope variables
param	Collection of all request parameter as single string value per parameter
paramValue	Collection of all request parameter as string array per parameter
header	Collection of all request header values as a single string value per header
headerValues	Collection of all request header values as string array per header.
cookie	Collection of all request cookie values as javax.servlet.http.Cookie value per cookie
intiParam	Collection of all application intialization parameter as single string value per value
pageContext	Instance of javax.servlet.jsp.Pagecontext class to access various request data.

Example:

    <%@ taglib uri="http://java.sun.com/jsp/jstl/functions"
    prefix="fn" %>
    <%@ taglib uri="http://java.sun.com/jsp/jstl/core"
    prefix="c" %>
    <html>
    <body>
    <form action="implicit1.jsp" method="GET">
    NAME:<input type="text" name="nam">
         <input type="submit">
    </form>
    <p><b>NAME</b>     : ${param.nam}</p>
    <p><b>HEADER</b>   : ${header["host"]}</p>
    <p><b>USER AGENT</b>:${header["user-agent"]}</p>
    </html>

Result:

    NAME : alex
    HEADER : localhost:8080
    USER AGENT:Mozilla/5.0 (Windows; U; Windows NT 5.1; 
    en-US; rv:1.9.0.15)Gecko/2009101601 Firefox/3.0.15 
    GTB5

In the above example we have used the implicit variables "param" and "header" to display the name entered, header, browser details etc.

Expression Language Implicit Variables in JSP.