Deactivating Expression Evaluation (The Java EE 5 Tutorial)

The Java EE 5 Tutorial

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.
Configure the page with the page directive.

To escape the #{ or ${ characters in the page, you use the \ character as follows:

some text \#{ some more\${ text
<my:tag someAttribute="sometext\#{more\${text" />

Another way to deactivate EL evaluation is by using a JSP property group to either allow the #{ characters as a String literal using the deferred-syntax-allowed-as-literal subelement, or to treat all expressions as literals using the el-ignored subelement:

<jsp-property-group>
    <deferred-syntax-allowed-as-literal>
        true
    </deferred-syntax-allowed-as-literal>
</jsp-property-group>

<jsp-property-group>
    <el-ignored>true</el-ignored>
</jsp-property-group>

Finally, you can configure the page with the page directive to either accept the #{ characters as String literals with the deferredSyntaxAllowedAsLiteral attribute, or to ignore all EL expressions using the isELIgnored attribute:

<%@page ... deferredSyntaxAllowedAsLiteral="true" %>

<%@ page isELIgnored ="true" %>

The valid values of these attributes are true and false. If isELIgnored 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 only if the attribute has rtexprvalue set to true or the expression is a deferred expression.

The default value of isELIgnored varies depending on the version of the web application deployment descriptor. The default mode for JSP pages delivered with a Servlet 2.4 descriptor is to evaluate EL expressions; this automatically provides the default that most applications want. The default mode for JSP pages delivered using a descriptor from Servlet 2.3 or before is to ignore EL expressions; this provides backward compatibility.