Setting Properties for Groups of JSP Pages - The J2EE 1.4 Tutorial

Setting Properties for Groups of JSP Pages

It is possible to specify certain properties for a group of JSP pages:

Expression language evaluation
Treatment of scripting elements (see Disabling Scripting)
Page encoding
Automatic prelude and coda includes

A JSP property group is defined by naming the group and specifying one or more URL patterns; all the properties in the group apply to the resources that match any of the URL patterns. If a resource matches URL patterns in more than one group, the pattern that is most specific applies. To define a property group using deploytool, follow these steps:

Select the WAR.
Select the JSP Properties tab.
Click the Add button next to the Name list.
Enter the name of the property group.
Click the Add button next to the URL Pattern list.
Enter the URL pattern (a regular expression, such as *.jsp).

The following sections discuss the properties and explain how they are interpreted for various combinations of group properties, individual page directives, and web application deployment descriptor versions.

Deactivating EL Expression Evaluation

Each JSP page has a default mode for EL expression evaluation. The default value varies depending on the version of the web application deployment descriptor. The default mode for JSP pages delivered using a Servlet 2.3 or earlier descriptor is to ignore EL expressions; this provides backward compatibility. 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. For tag files (see Encapsulating Reusable Content Using Tag Files), the default is to always evaluate expressions.

You can override the default mode through the isELIgnored attribute of the page directive in JSP pages and through the isELIgnored attribute of the tag directive in tag files. You can also explicitly change the default mode by setting the value of the EL Evaluation Ignored checkbox in the JSP Properties tab. Table 12-5 summarizes the EL evaluation settings for JSP pages and their meanings.

Table 12-5 EL Evaluation Settings for JSP Pages 

JSP Configuration	Page Directive isELIgnored	EL Encountered
Unspecified	Unspecified	Evaluated if 2.4 web.xml Ignored if <= 2.3 web.xml
false	Unspecified	Evaluated
true	Unspecified	Ignored
Overridden by page directive	false	Evaluated
Overridden by page directive	true	Ignored

Table 12-6 summarizes the EL evaluation settings for tag files and their meanings.

Table 12-6 EL Evaluation Settings for Tag Files 

Tag Directive isELIgnored	EL Encountered
Unspecified	Evaluated
false	Evaluated
true	Ignored

Declaring Page Encodings

You set the page encoding of a group of JSP pages by selecting a page encoding from the Page Encoding drop-down list. Valid values are the same as those of the pageEncoding attribute of the page directive. A translation-time error results if you define the page encoding of a JSP page with one value in the JSP configuration element and then give it a different value in a pageEncoding directive.

Defining Implicit Includes

You can implicitly include preludes and codas for a group of JSP pages by adding items to the Include Preludes and Codas lists. Their values are context-relative paths that must correspond to elements in the web application. When the elements are present, the given paths are automatically included (as in an include directive) at the beginning and end, respectively, of each JSP page in the property group. When there is more than one include or coda element in a group, they are included in the order they appear. When more than one JSP property group applies to a JSP page, the corresponding elements will be processed in the same order as they appear in the JSP configuration section.

For example, the Duke's Bookstore application uses the files /template/prelude.jspf and /template/coda.jspf to include the banner and other boilerplate in each screen. To add these files to the Duke's Bookstore property group using deploytool, follow these steps:

Define a property group with name bookstore2 and URL pattern *.jsp.
Click the Edit button next to the Include Preludes list.
Click Add.
Enter /template/prelude.jspf.
Click OK.
Click the Edit button next to the Include Codas list.
Click Add.
Enter /template/coda.jspf.
Click OK.

Preludes and codas can put the included code only at the beginning and end of each file. For a more flexible approach to building pages out of content chunks, see A Template Tag Library.

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