JSP Tutorials - Herong's Tutorial Examples - Version 4.03, by Dr. Herong Yang
EL Expression Types and Usage
This section describes EL expression types and their usage. Rvalue Immediate Evaluated Value expressions are commonly used in JSP pages mixed in static text and tag attributes.
According to the EL 2.1 specification, an EL expression can be grouped in 3 ways:
Most commonly used EL expressions in JSP pages are Rvalue Immediate Evaluated Value expressions (Immediate Evaluation Expression, Value Expression and Rvalue Expression), which are expressed as:
${expression}
Since JSP 2.0, Rvalue Immediate Evaluated Value EL expressions can be used in 2 areas in JSP pages:
1. Using EL in Static Text - EL expressions can be used anywhere in the static text. Values resulted from EL expressions will be converted to String and inserted into the static text. For example, hello_el.jsp:
<html><body> ${"Hello world! - From EL"} </body></html>
2. Using EL in Tag Attributes - EL expressions can be used any tag attributes where expression is accepted. Values resulted from EL expressions will be passed to the tag class to determine how it will be used. For example, hello_tag_el.jsp:
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %> <html><body> <c:out value="${'Hello world! - From Tag EL'}"/> </body></html>
In this chapter, we will concentrate on using EL expressions in static text to learn basic elements of EL expressions.
Last update: 2012.
Table of Contents
JSP (JavaServer Pages) Overview
Tomcat 7 Installation on Windows Systems
Syntax of JSP Pages and JSP Documents
JavaBean Objects and "useBean" Action Elements
Managing HTTP Response Header Lines
Non-ASCII Characters Support in JSP Pages
What is EL (Expression Language)?
►EL Expression Types and Usage
Literal Data and Named Variables
Basic Operators and Operations
Collection Elements and Object Properties
Expression Examples in Static Text
Expression Examples in Static Text - Result
EL Variables Are pageContext Attributes
Overview of JSTL (JSP Standard Tag Libraries)