![Expression Language (EL)
Here expr specifies the expression itself. The most
common operators in JSP EL are . and []. These two
operators allow you to access various attributes of Java
Beans and built-in JSP objects.
For example above syntax <jsp:setProperty> tag can be
written with an expression like:
<jsp:setProperty name="box" property="perimeter"
value="${2*box.width+2*box.height}"/>
When the JSP compiler sees the ${} form in an attribute,
it generates code to evaluate the expression and
substitutes the value of expression.](https://image.slidesharecdn.com/javabeans-131114005559-phpapp01/85/Java-beans-5-320.jpg)
![Operators in EL
Operator
Description
.
Access a bean property or Map entry
[]
Access an array or List element
()
Group a sub-expression to change the evaluation order
+
Addition
-
Subtraction or negation of a value
*
Multiplication
/ or div
Division
%
Modulo (remainder)
== or eq
Test for equality
!= or ne
Test for inequality
< or lt
Test for less than
> or gt
Test for greater than
<= or le
Test for less than or equal
>= or gt
Test for greater than or equal](https://image.slidesharecdn.com/javabeans-131114005559-phpapp01/85/Java-beans-7-320.jpg)
Java beans
- 1. Java Beans
- 2. What are Java Beans? JavaBean is a specially constructed Java class written in the Java and coded according to the JavaBeans API specifications. Characteristics of a JavaBean: It provides a default, no-argument constructor. It should be serializable and implement the Serializable interface. It may have a number of properties which can be read or written. It may have a number of "getter" and "setter" methods for the properties.
- 3. JavaBeans Properties A JavaBean property may be read, write, read only, or write only. JavaBean properties are accessed through two methods getPropertyName() For example, if property name is firstName, your method name would be getFirstName() to read that property. This method is called accessor. setPropertyName() For example, if property name is firstName, your method name would be setFirstName() to write that property. This method is called mutator.
- 4. Expression Language (EL) Expression Language (EL) makes it possible to easily access application data stored in JavaBeans components. Arithmetic logical Within a JSP EL expression, you can use integers, floating point numbers, strings, the built-in constants true and false for boolean values, and null. JSP EL allows you to specify an expression for any of these attribute values. A simple syntax for JSP EL is as follows: ${expr}
- 5. Expression Language (EL) Here expr specifies the expression itself. The most common operators in JSP EL are . and []. These two operators allow you to access various attributes of Java Beans and built-in JSP objects. For example above syntax <jsp:setProperty> tag can be written with an expression like: <jsp:setProperty name="box" property="perimeter" value="${2*box.width+2*box.height}"/> When the JSP compiler sees the ${} form in an attribute, it generates code to evaluate the expression and substitutes the value of expression.
- 6. Expression Language (EL) You can include a JSP EL expression in the body of a <jsp:text> tag (or any other tag) with the same ${} syntax you use for attributes. <jsp:text> Box Perimeter is: ${2*box.width + 2*box.height} </jsp:text> To deactivate the evaluation of EL expressions, we specify the isELIgnored attribute of the page directive as below: <%@ page isELIgnored ="true|false" %> If it is true, EL expressions are ignored when they appear in static text or tag attributes. If it is false, EL expressions are evaluated by the container.
- 7. Operators in EL Operator Description . Access a bean property or Map entry [] Access an array or List element () Group a sub-expression to change the evaluation order + Addition - Subtraction or negation of a value * Multiplication / or div Division % Modulo (remainder) == or eq Test for equality != or ne Test for inequality < or lt Test for less than > or gt Test for greater than <= or le Test for less than or equal >= or gt Test for greater than or equal
- 8. Operators in EL Operator Description && or and Test for logical AND || or or Test for logical OR ! or not Unary Boolean complement empty Test for empty variable values