JSP Expression Language
Expression Language(EL) was added to JSP 2.0 specification. The purpose of EL is to produce scriptless JSP pages. The syntax of EL in a JSP is as follows:
${expr}
Here expr is a valid EL expression. An expression can be mixed with static text/values and can also be combined with other expressions to form larger expression.
![expression language example]()
How EL expression is used?
EL expression can be used in two ways in a JSP page
- As attribute values in standard and custom tags. Example:
<jsp:include page="${location}">
Where location variable is separately defines in the jsp page.
Expressions can also be used in jsp:setProperty to set a properties value, using other bean properties like : If we have a bean named Square with properties length, breadth and area.
<jsp:setProperty name="square" property="area" value="${square.length*square.breadth}" />
- To output in HTML tag:
<h1>Welcome ${name}</h1>
To deactivate the evaluation of EL expressions, we specify the isELIgnored attribute of the page directive as below:
<%@ page isELIgnored ="true|false" %>
JSP EL Implicit Objects
Following are the implicit objects in EL :
| Implicit Object | Description |
|---|
| pageContext | It represents the PageContext object. |
| pageScope | It is used to access the value of any variable which is set in the Page scope |
| requestScope | It is used to access the value of any variable which is set in the Request scope. |
| sessionScope | It is used to access the value of any variable which is set in the Session scope |
| applicationScope | It is used to access the value of any variable which is set in the Application scope |
| param | Map a request parameter name to a single value |
| paramValues | Map a request parameter name to corresponding array of string values. |
| header | Map containing header names and single string values. |
| headerValues | Map containing header names to corresponding array of string values. |
| cookie | Map containing cookie names and single string values. |
Example of JSP EL
Let's take a simple example for understanding the JSP expression language,
index.jsp
<form method="POST" action="welcome.jsp">
Name <input type="text" name="user" >
<input type="submit" value="Submit">
</form>
welcome.jsp
<html>
<head>
<title>Welcome Page</title>
</head>
<body>
<h1>Welcome ${param.name}</h1>
</body>
</html>
Arithmetic Operations available in EL
Following are the arithmetic operators avilable in EL:
| Arithmetic Operation | Operator |
|---|
| Addition | + |
| Substraction | - |
| Multiplication | * |
| Division | / and div |
| Remainder | % and mod |
Logical and Relational Operators available in EL
Following are the logical operator and comparators avilable in EL:
| Logical and Relational Operator | Operator |
|---|
| Equals | == and eq |
| Not equals | != and ne |
| Less Than | < and lt |
| Greater Than | > and gt |
| Greater Than or Equal | >= and ge |
| Less Than or Equal | <= and le |
| and | && and and |
| or | || and or |
| not | ! and not |
