The Java EE 5 Tutorial (PDF) - Oracle Software Downloads

ProgrammingTagsThat Accept Scripting Elements
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TagsThat DefineVariables
The mechanisms for defining variables in classic tags are similar to those described in
Chapter 8, “Custom Tags in JSP Pages.” You must declare the variable in a variable element of
the TLD or in a tag extra info class. Use PageContext().setAttribute(name,value) or
PageContext.setAttribute(name,value,scope) methods in the tag handler to create or
update an association between a name that is accessible in the page context and the object that is
the value of the variable. For classic tag handlers, Table 9–3 illustrates how the availability of a
variable affects when you may want to set or update the variable’s value.
TABLE 9–3 Variable Availability
Value Availability In Methods
NESTED Between the start tag and the end tag doStartTag, doInitBody, and doAfterBody
AT_BEGIN From the start tag until the end of the page doStartTag, doInitBody, doAfterBody, and
doEndTag
AT_END After the end tag until the end of the page doEndTag
A variable defined by a custom tag can also be accessed in a scripting expression. For example,
the web service described in the preceding section can be encapsulated in a custom tag that
returns the response in a variable named by the var attribute, and then var can be accessed in a
scripting expression as follows:
!
Remember that in situations where scripting is not allowed (in a tag body where the
body-content is declared as scriptless and in a page where scripting is specified to be
invalid), you wouldn’t be able to access the variable in a scriptlet or an expression. Instead, you
would have to use the JSP expression language to access the variable.
The Java EE 5Tutorial • June 2010