Setting Properties for Groups of JSP Pages

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 in a deployment descriptor, follow these steps:

Include a jsp-config element if the deployment descriptor doesn't already have one.

Add a jsp-property-group element inside the jsp-config element.

Add a display-name element inside the jsp-property-group element and give it a name.

Add a url-pattern element inside the jsp-property-group element and give it a 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, page 204), 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 adding an el-ignored element to the jsp-property-group element in the deployment descriptor. Table 4-8 summarizes the EL evaluation settings for JSP pages and their meanings.

Table 4-8 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 4-9 summarizes the EL evaluation settings for tag files and their meanings.

Table 4-9 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 adding a page-encoding element to the jsp-property-group element in the deployment descriptor and setting its value to one of the valid character encoding codes, which are the same as those accepted by 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 the deployment descriptor, follow these steps:

Add a jsp-property-group element with name bookstore2 and URL pattern *.jsp.

Add an include-prelude element to the jsp-property-group element and give it the name of the file to include, in this case, /template/prelude.jspf.

Add an include-code element to the jsp-property-group element and give it the name of the file to include, in this case, /template/coda.jspf.

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 (page 244).

Eliminating Extra White Space

Whitespaces included in the template text of JSP pages is preserved by default. This can have undesirable effects. For example, a carriage return added after a taglib directive would be added to the response output as an extra line.

If you want to eliminate the extra white space from the page, you can add a trim-directive-whitespaces element to a jsp-property-group element in the deployment descriptor and set it to true.

Alternatively, a page author can set the value of the trimDirectiveWhitespaces attribute of the page directive to true or false. This will override the value specified in the deployment descriptor.

Custom tag authors can eliminate white space from the output generated by a tag file by setting the trimDirectiveWhiteSpace attribute of the tag directive to true.