[Jakarta-taglibs Wiki] Update of "ReusableDialogComponents/Tutorials/Composition" by RahulAkolkar

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The following page has been changed by RahulAkolkar:
http://wiki.apache.org/jakarta-taglibs/ReusableDialogComponents/Tutorials/Composition

New page:
''Where the whole is greater than the sum of its parts''

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Since all components use JSP 2.0 tag files for their implementations, it is possible to easily create components which are composed of smaller ones. Thus, a composite can embed functionality already provided by (usually, more than one) other components, and add value by enabling reuse, since a composite now becomes a first-class component in its own right, defining the dialog management across its children, the public data model that gets returned etc.

 * Example:
{{{
<rdc:mortgage id="myMortgage" />
}}}

 * Where composition comes in
The guts of the mortgage composite contains this:
{{{
<rdc:group id="mortgageGroup" strategy="org.apache.taglibs.rdc.dm.SimpleDirectedDialog">
  <rdc:mortgageType id="myMortgageType" ... />
  <rdc:percent id="myPercentageDownpayment" ... />
</rdc:group>
}}}
where ... stands for other tag attributes not relevant to this discussion.

 * Interpretation
{{{
Collect mortgage information, which due to the composition, means, collect a mortgage type and a percentage down payment (with constraints as specified by tag attributes), in that order.
}}}

Composites can contain other composites, so it is possible to recursively encapsulate larger bits of interaction within a single composite. The design decision regarding the optimum size of a component depends on factors such as how composition affects configurability, how much reuse across JSPs / applications is expected if further composition is pursued etc.

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