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Java Enterprise Best Practices
book

Java Enterprise Best Practices

by O'Reilly Java Authors
December 2002
Intermediate to advanced content levelIntermediate to advanced
288 pages
9h 46m
English
O'Reilly Media, Inc.
Content preview from Java Enterprise Best Practices

Consider Developing a Tag Library Validator

To make the page author’s life as easy as possible, you should consider implementing a tag library validator for your custom tag library. This type of validator was introduced in JSP 1.2, and it can do a much better job verifying that all custom actions are used correctly than the previous mechanism (the TagExtraInfo class) could.

You implement a tag library validator by extending javax.servlet.jsp.tagext.TagLibraryValidator and provide an implementation for the abstract validate( ) method:

public ValidationMessage[  ] validate(String prefix, String uri, PageData pd)

The container calls this method when it translates the page into a servlet. The parameters provide the validator with the tag library prefix, URI (declared by the taglib directive in the page), and, most importantly, a PageData instance. Through the PageData instance, the validator gains access to an XML representation of the complete page (called an XML view). With access to the full page in a format that’s easy to parse, it can make sure the actions are properly nested and appear in the right order, in addition to what’s always been possible: checking the proper use of all attributes for each individual custom action element.

The validate( ) method returns an array of ValidationMessage objects. Each object represents a validation error, containing a text message plus a unique element ID that the container can use to map the error message to the location of the corresponding ...

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Publisher Resources

ISBN: 0596003846Supplemental ContentErrata Page