| Information on the scripting variables that are created/modified by
a tag (at run-time). This information is provided by TagExtraInfo
classes and it is used by the translation phase of JSP.
Scripting variables generated by a custom action have an associated
scope of either AT_BEGIN, NESTED, or AT_END.
The class name (VariableInfo.getClassName) in the returned objects
is used to determine the types of the scripting variables.
Note that because scripting variables are assigned their values
from scoped attributes which cannot be of primitive types,
"boxed" types such as java.lang.Integer must
be used instead of primitives.
The class name may be a Fully Qualified Class Name, or a short
class name.
If a Fully Qualified Class Name is provided, it should refer to a
class that should be in the CLASSPATH for the Web Application (see
Servlet 2.4 specification - essentially it is WEB-INF/lib and
WEB-INF/classes). Failure to be so will lead to a translation-time
error.
If a short class name is given in the VariableInfo objects, then
the class name must be that of a public class in the context of the
import directives of the page where the custom action appears.
The class must also be in the CLASSPATH for the Web Application
(see Servlet 2.4 specification - essentially it is WEB-INF/lib and
WEB-INF/classes). Failure to be so will lead to a translation-time
error.
Usage Comments
Frequently a fully qualified class name will refer to a class that
is known to the tag library and thus, delivered in the same JAR
file as the tag handlers. In most other remaining cases it will
refer to a class that is in the platform on which the JSP processor
is built (like J2EE). Using fully qualified class names in this
manner makes the usage relatively resistant to configuration
errors.
A short name is usually generated by the tag library based on some
attributes passed through from the custom action user (the author),
and it is thus less robust: for instance a missing import directive
in the referring JSP page will lead to an invalid short name class
and a translation error.
Synchronization Protocol
The result of the invocation on getVariableInfo is an array of
VariableInfo objects. Each such object describes a scripting
variable by providing its name, its type, whether the variable is
new or not, and what its scope is. Scope is best described through
a picture:
The JSP 2.0 specification defines the interpretation of 3 values:
- NESTED, if the scripting variable is available between
the start tag and the end tag of the action that defines it.
-
AT_BEGIN, if the scripting variable is available from the start tag
of the action that defines it until the end of the scope.
- AT_END, if the scripting variable is available after the end tag
of the action that defines it until the end of the scope.
The scope value for a variable implies what methods may affect its
value and thus where synchronization is needed as illustrated by
the table below. Note: the synchronization of the variable(s)
will occur after the respective method has been called.
Variable Synchronization
Points
|
| |
doStartTag() |
doInitBody() |
doAfterBody() |
doEndTag() |
doTag() |
Tag
|
AT_BEGIN, NESTED
|
|
|
AT_BEGIN, AT_END
|
|
IterationTag
|
AT_BEGIN, NESTED
|
|
AT_BEGIN, NESTED
|
AT_BEGIN, AT_END
|
|
BodyTag
|
AT_BEGIN, NESTED1
|
AT_BEGIN, NESTED1
|
AT_BEGIN, NESTED
|
AT_BEGIN, AT_END
|
|
SimpleTag
|
|
|
|
|
AT_BEGIN, AT_END
|
1 Called after doStartTag() if
EVAL_BODY_INCLUDE is returned, or after
doInitBody() otherwise.
Variable Information in the TLD
Scripting variable information can also be encoded directly for most cases
into the Tag Library Descriptor using the <variable> subelement of the
<tag> element. See the JSP specification.
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