| bean |
This tag library contains tags useful in accessing beans and their
properties, as well as defining new beans (based on these accesses)
that are accessible to the remainder of the page via scripting variables
and page scope attributes. Convenient mechanisms to create new beans
based on the value of request cookies, headers, and parameters are also
provided.Many of the tags in this tag library will throw a
JspException at runtime when they are utilized incorrectly
(such as when you specify an invalid combination of tag attributes). JSP
allows you to declare an "error page" in the <%@ page %>
directive. If you wish to process the actual exception that caused the
problem, it is passed to the error page as a request attribute under key
org.apache.struts.action.EXCEPTION.If you are viewing this page from within the Struts Documentation
Application (or online at
http://struts.apache.org/), you can learn more about using
these tags in the
Bean Tags Developer's Guide.
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| logic |
This tag library contains tags that are useful in managing conditional
generation of output text, looping over object collections for
repetitive generation of output text, and application flow management.For tags that do value comparisons (equal,
greaterEqual, greaterThan, lessEqual,
lessThan, notEqual), the following rules apply:The specified value is examined. If it can be converted successfully
to a double or a long, it is assumed that the
ultimate comparison will be numeric (either floating point or integer).
Otherwise, a String comparison will be performed.The variable to be compared to is retrieved, based on the selector
attribute(s) (cookie, header,
name, parameter, property)
present on this tag. It will be converted to the appropriate type
for the comparison, as determined above.If the specified variable or property returns null, it will be
coerced to a zero-length string before the comparison occurs.The specific comparison for this tag will be performed, and the nested
body content of this tag will be evaluated if the comparison returns
a true result.For tags that do substring matching (match,
notMatch), the following rules apply:The specified variable is retrieved, based on the selector attribute(s)
(cookie, header, name,
parameter, property) present on this tag.
The variable is converted to a String, if necessary.A request time exception will be thrown if the specified variable
cannot be retrieved, or has a null value.The specified value is checked for existence as a substring of the
variable, in the position specified by the location
attribute, as follows: at the beginning (if location is set to
start), at the end (if location is set to
end), or anywhere (if location is not specified).Many of the tags in this tag library will throw a
JspException at runtime when they are utilized incorrectly
(such as when you specify an invalid combination of tag attributes). JSP
allows you to declare an "error page" in the <%@ page %>
directive. If you wish to process the actual exception that caused the
problem, it is passed to the error page as a request attribute under key
org.apache.struts.action.EXCEPTION.
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| nested |
[Since Struts 1.1]This tag library brings a nested context to the functionality of the
Struts custom tag library.It's written in a layer that extends the current Struts tags, building on
their logic and functionality. The layer enables the tags to be aware of the
tags which surround them so they can correctly provide the nesting property
reference to the Struts system.
It's all about nesting beans...
A bean holds a reference to another bean internally, and all access to that
bean is handled through the current bean. This act of having one bean's
access go through another bean is known as "nesting beans". The first bean
is known as the parent bean. The bean which it references, is known as a
child bean. The terms "parent" and "child" are commonly used to describe the
model's hierarchy.
A simple example...
Take an object which represents a monkey. The monkey's job is to pick
bunches of bananas. On each bunch picked hangs many bananas. If this case
was translated to bean objects, the monkey object would have a reference to
the bunch objects he picked, and each bunch object would hold a reference
to the bananas hanging in the bunch.
To describe this...
The monkey object is the parent to the bunch object, and the bunch object
is a child of the monkey object. The bunch object is parent to its child
banana objects, and the child banana objects children of the bunch object.
The monkey is higher in the hierarchy than the bananas, and the bananas
lower in the hierarchy to the bunches.
One special term to remember is for the most parent class, which is known
as the "root" object which starts the hierarchy.Nested tags are all about efficiently managing this style of hierarchy
structure within your JSP markup.Important Note: Nearly all these tags extend tags from
other libraries to bring their functionality into the nested context.
Nesting relies on the tags working against the one bean model, and managing
the properties so that they become relative to the properties they are
nested within. In doing so, the tags will set the "name" attribute internally
(where applicable), and in many cases will rely on the "property" attribute
being set so it can be updated internally to become nested. The original tags
on occasion provide options that don't use the "name" and "property"
attributes. These uses will then fall outside the nested context, and will
most likely cause error. To take advantage of these options, markup using
the original tag for these cases. For an example see the
<nested:options> tag.
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