| Translation-time validator class for a JSP page.
A validator operates on the XML view associated with the JSP page.
The TLD file associates a TagLibraryValidator class and some init
arguments with a tag library.
The JSP container is reponsible for locating an appropriate
instance of the appropriate subclass by
- new a fresh instance, or reuse an available one
- invoke the setInitParams(Map) method on the instance
once initialized, the validate(String, String, PageData) method will
be invoked, where the first two arguments are the prefix
and uri for this tag library in the XML View. The prefix is intended
to make it easier to produce an error message. However, it is not
always accurate. In the case where a single URI is mapped to more
than one prefix in the XML view, the prefix of the first URI is provided.
Therefore, to provide high quality error messages in cases where the
tag elements themselves are checked, the prefix parameter should be
ignored and the actual prefix of the element should be used instead.
TagLibraryValidators should always use the uri to identify elements
as beloning to the tag library, not the prefix.
A TagLibraryValidator instance
may create auxiliary objects internally to perform
the validation (e.g. an XSchema validator) and may reuse it for all
the pages in a given translation run.
The JSP container is not guaranteed to serialize invocations of
validate() method, and TagLibraryValidators should perform any
synchronization they may require.
As of JSP 2.0, a JSP container must provide a jsp:id attribute to
provide higher quality validation errors.
The container will track the JSP pages
as passed to the container, and will assign to each element
a unique "id", which is passed as the value of the jsp:id
attribute. Each XML element in the XML view available will
be extended with this attribute. The TagLibraryValidator
can then use the attribute in one or more ValidationMessage
objects. The container then, in turn, can use these
values to provide more precise information on the location
of an error.
The actual prefix of the id attribute may or may not be
jsp but it will always map to the namespace
http://java.sun.com/JSP/Page. A TagLibraryValidator
implementation must rely on the uri, not the prefix, of the id
attribute.
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