The Java EE 5 Tutorial (PDF) - Oracle Software Downloads

Unified Expression Language
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they accept and the type definitions of the attributes that must be added to the TLD. You cannot
use #{} syntax for a dynamic attribute, meaning an attribute that accepts
dynamically-calculated values at runtime. Section 2.3.2 of the JavaServer Pages 2.1 specification
refers to these attributes. Neither can you use the ${} syntax for a deferred attribute.
TABLE 5–2 Definitions of Tag Attributes That Accept EL Expressions
AttributeType Example Expression Type Attribute Definition
dynamic "literal" true
${literal} true
deferred value "literal"
java.lang.String
#{customer.age}
int
deferred method "literal"
java.lang.String submit()
#{customer.calcTotal}
double calcTotal(int, double)
In addition to the tag attribute types shown in Table 5–2, you can also define an attribute to
accept both dynamic and deferred expressions. In this case, the tag attribute definition contains
both an rtexprvalue definition set to true and either a deferred-value or deferred-method
definition.
Deactivating Expression Evaluation
Because the patterns that identify EL expressions, ${ } and #{ }, were not reserved in the JSP
specifications before JSP 2.0, there might exist applications in which such patterns are intended
to pass through verbatim. To prevent the patterns from being evaluated, you can deactivate EL
evaluation using one of the following methods:
■ Escape the #{ or ${ characters in the page.
■ Configure the application with a JSP Property Group.
The Java EE 5Tutorial • June 2010