[jbossseam-issues] [JBoss JIRA] Created: (JBSEAM-2221) Introduce way to retrieve proxy object of a Seam JavaBean Component
Introduce way to retrieve proxy object of a Seam JavaBean Component
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Key: JBSEAM-2221
URL: http://jira.jboss.com/jira/browse/JBSEAM-2221
Project: JBoss Seam
Issue Type: Feature Request
Reporter: Wolfgang Schwendt
The EJB programming model requires that a Session Bean never passes a
"this"-pointer to other client objects. Instead,
javax.ejb.SessionContext provides a method getBusinessObject(). If a SessionBean wants to
pass a reference pointing to itself to other clients, it first has to retrieve its own EJB
object reference by calling SessionContext.getBusinessObject() which it then can pass to
other beans. This reference returned by javax.ejb.SessionContext.getBusinessObject() is
the equivalent to Java's this pointer.
With respect to Seam's interceptor framework, such a feature is missing as far as
normal JavaBean components are concerned. It leads to subtle programming errors:
Consider the implementation of org.jboss.seam.framework.Query. getDataModel():
/**
* Wrap the result set in a JSF {@link DataModel}
*
* Delegates to {@link DataModels#getDataModel(Query)}
*
*/
@Transactional
public DataModel getDataModel()
{
if (dataModel==null)
{
dataModel = DataModels.instance().getDataModel(this);
}
return dataModel;
}
This method method passes a "this"-reference to the
org.jboss.seam.faces.dataModels Seam-component.
But this can lead to a behavior not expected by the programmer. If the
(Entity)Query-component gets instantiated as a conversation-scoped component, Seam wraps
the ManagedEntityIdentityInterceptor around this Query component.
After each method invocation intercepted by the ManagedEntityIdentityInterceptor, the
ManagedEntityIdentityInterceptor saves wrappers for all contained Entity references in the
conversation context and sets the corresponding reference fields in the Query component to
null.
Now, consider again above implementation of Query.getDataModel(). Because a
"this" pointer is passed to the dataModels-component, any calls conducted by the
datamodel-component via this reference won't (!) be routed through the
ManagedEntityIdentity interceptor. Hence, when the datamodel-component calls the
Query-component via the Java-this pointer it received previously, the
ManagedEntityIdentity won't be invoked and in turn the Entity reference fields in the
Query-component won't be restored.
This leads to a bug as described in JBSEAM-1814. In order to fix that bug, we would have
to change the implementation of Query. getDataModel(). Rather than passing the Java-this
pointer to the dataModels component, the correct implementation would be as follows. The
Query component would first have to retrieve a reference to its own proxy object, which it
then could pass to the dataModels component.
Summary: For JavaBean Seam components we need a feature similar to
SessionContext.getBusinessObject(), to enable a JavaBean Seam component to pass a proxy
reference to itself to other Seam components instead of passing directly the Java-this
pointer.
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