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Expression Language


The Expression Language (EL) simplifies the accessibility of data stored in the Java Bean component, and other objects like request, session, application etc.

There are many implicit objects, operators and reserve words in EL.

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

 

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 }

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. <a href=“process.jsp”>visit</a>

process.jsp

  1. Value is ${ sessionScope.user }

Precedence of Operators in EL

There are many operators that have been provided in the Expression Language. Their precedence are as follows:

[] .
()
-(unary) not ! empty
* / div % mod
+ – (binary)
< <= > >= lt le gt ge
== != eq ne
&& and
|| or
?:

Reserve words in EL

There are many reserve words in the Expression Language. They are as follows:

lt le gt ge
eq ne true false
and or not instanceof
div mod empty null

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