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Experiments with EJB3 annotation + DD merging in AS7
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created by <a href="http://community.jboss.org/people/jaikiran">jaikiran pai</a> in <i>JBoss AS7 Development</i> - <a href="http://community.jboss.org/docs/DOC-16688">View the full document</a>
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<div class="jive-rendered-content"><h4>Purpose:</h4><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>This document outlines the issues encountered while trying to implement merging of EJB3 deployment descriptor and annotations for AS 7.0.0.Beta2</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><h4>Details:</h4><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><h5>Pre-AS7 deployers and metdata merging:</h5><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>Typically the way we used to create a merged view of deployment descriptor (DD) values with annotation values involved the following:</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><ul><li>2 separate views were maintained during deployment processing. One view corresponding to DD values and the other for annotations</li><li>After a certain point, the 2 views would be merged into one </li><li>After that point, the deployers which required to work on the metadata, would start using the merged view of the metadata</li></ul><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><h5>AS7 Deployment Unit Processors (DUPs):</h5><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>The previous mentioned steps would ideally have worked out in the current AS7 DUP framework. However, most (all?) of the EE specific DUPs which work on annotations expect the metadata (== *ComponentDescription) to be available. For example, see the ResourceInjectionAnnotationParsingProcessor. It gets hold of a AbstractComponentDescription and starts looking for annotations on that component class. The AbstractComponentDescription is fetched from the EEModuleDescription and leads to a chicken and egg problem. For example, while working on EJB3 DD + annotation merging, this is what I initially tried:</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><ol><li>Various (ordered) EJB DD processing DUPs running first and creating the EJBComponentDescription(s).</li><li>Various (ordered) annotation DUPs running after the DD based DUPs and creating a parallel EJBComponentDescription(s).</li><li>A merging DUP which merges the EJBComponentDescription(s) created in #1 and #2 and then attaching each of these EJBComponentDescriptions to EEModuleDescription.</li><li>Rest of the DUPs then working off the merged EJBComponentDescription(s) by fetching them from the EEModuleDescription.</li></ol><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>The problem with this approach is that the DUPs like ResourceInjectionAnnotationParsingProcessor which scan for annotations require the EJBComponentDescription to be available in EEModuleDescription for it to fire. Effectively, until #3 is done (the merging of DD + annotations), such DUPs can't fire. However, for #3 (a.k.a merging) to be successfully completed we need the ResourceInjectionAnnotationParsingProcessor and such DUPs to fire. Effectively this leads to a chicken and egg issue.</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>There's one other approach which I tried out (with issues of its own), the one which is currently implemented (and broken) in upstream, for merging DD + annotations. That approach was more of a workaround for this main issue and isn't really relevant at this point. However, I can outline that approach here if required (just need to recap some finer details on why it is broken)</p></div>
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