JSP Expression Language (EL)

What is Expression Language?

Expression Language (EL) was introduced in JSP 2.0 to simplify access to data stored in JavaBeans, request parameters, session attributes, and other objects. EL expressions use the syntax ${expression} and can be used directly in HTML without scriptlets.

EL makes JSP pages cleaner and easier to maintain by eliminating verbose Java code like <%= (String) session.getAttribute("user") %> and replacing it with ${sessionScope.user}.

EL Implicit Objects

EL Object	Type	Description
`param`	Map<String,String>	Request parameters (single value)
`paramValues`	Map<String,String[]>	Request parameters (multiple values)
`header`	Map<String,String>	HTTP request headers
`headerValues`	Map<String,String[]>	HTTP headers (multiple values)
`cookie`	Map<String,Cookie>	Cookies from the request
`pageScope`	Map	Page-scoped attributes
`requestScope`	Map	Request-scoped attributes
`sessionScope`	Map	Session-scoped attributes
`applicationScope`	Map	Application-scoped attributes
`initParam`	Map	Context init parameters from web.xml
`pageContext`	PageContext	Access to JSP page context

EL Syntax and Implicit Objects

<%@ page language="java" contentType="text/html; charset=UTF-8"%>
<%
    // Set attributes in different scopes
    request.setAttribute("message", "Hello from Request!");
    session.setAttribute("username", "Alice");
    session.setAttribute("age", 25);
    application.setAttribute("appVersion", "2.0");
%>
<html><body>

<h3>Accessing Scoped Attributes</h3>
<p>Request: ${requestScope.message}</p>
<p>Session username: ${sessionScope.username}</p>
<p>Session age: ${sessionScope.age}</p>
<p>App version: ${applicationScope.appVersion}</p>

<%-- EL searches all scopes automatically (page, request, session, app) --%>
<p>Auto-search: ${username}</p>

<h3>Request Parameters</h3>
<p>Name param: ${param.name}</p>
<p>Age param: ${param.age}</p>

<h3>Headers and Cookies</h3>
<p>User-Agent: ${header['User-Agent']}</p>
<p>Cookie value: ${cookie.JSESSIONID.value}</p>

<h3>pageContext</h3>
<p>Context path: ${pageContext.request.contextPath}</p>
<p>Server name: ${pageContext.request.serverName}</p>

</body></html>

EL Operators

EL supports arithmetic, relational, logical, and the empty operator:

EL Operators

<%@ page language="java" contentType="text/html; charset=UTF-8"%>
<html><body>

<h3>Arithmetic Operators</h3>
<p>10 + 5 = ${10 + 5}</p>
<p>10 - 3 = ${10 - 3}</p>
<p>4 * 3 = ${4 * 3}</p>
<p>10 / 3 = ${10 / 3}</p>
<p>10 mod 3 = ${10 mod 3}</p>

<h3>Relational Operators</h3>
<p>5 == 5: ${5 == 5}</p>
<p>5 != 3: ${5 != 3}</p>
<p>10 > 5: ${10 gt 5}</p>
<p>3 < 7: ${3 lt 7}</p>
<p>5 >= 5: ${5 ge 5}</p>

<h3>Logical Operators</h3>
<p>true && false: ${true and false}</p>
<p>true || false: ${true or false}</p>
<p>!true: ${not true}</p>

<h3>Empty Operator</h3>
<p>Is null empty: ${empty null}</p>
<p>Is "" empty: ${empty ""}</p>
<p>Is "hello" empty: ${empty "hello"}</p>

<h3>Ternary / Conditional</h3>
<p>${param.age gt 18 ? "Adult" : "Minor"}</p>

</body></html>

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JSP Expression Language (EL)

What is Expression Language?

EL Implicit Objects

EL Operators

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