[jaxrs-dev] Request for extension with Application interface

[Ron Sigal <rsigal@xxxxxxxxxx>]

This issue came up in the context of 
https://issues.jboss.org/browse/RESTEASY-1709 "Same JAX-RS Application 
instance injected across applications".

Consider a WAR with two Application classes, Application1 and 
Application2, both derived from ApplicationAbstract and both of which 
reference a provider such as

@Provider
public class FooReader implements MessageBodyReader<Foo> {

   @Context
   ApplicationAbstract application;
   ...
}

The value of application should be either Application1 or Application2, 
depending on the resource being called. In accordance with Section 4.1 
"Lifecycle and Environment" of the JAX-RS 2.1 spec, which says, "By 
default a single instance of each provider class is instantiated for 
each JAX-RS application", RESTEasy creates two copies of FooReader at 
initialization time and injects the appropriate Application.

The complication arises when CDI is activated. With respect to CDI, the 
application scope of FooReader means that a single instance of FooReader 
will be created for the lifetime of the WAR, and injection into the 
application field will occur only once. Whichever value is injected will 
be correct some of the time and incorrect some of the time.

The natural solution would be to inject a proxy which retrieves the 
currently relevant Application, but, unfortunately, unlike all of the 
other @Context injectable types, Application is a class instead of an 
interface. In RESTEasy, we worked around that by using Javassist, which 
is able to create proxies for classes. It would be preferable, though, 
if it were possible to use pure Java proxies.

We propose something like

   public interface ApplicationInt {

      public Set<Class<?>> getClasses();

      public Set<Object> getSingletons();

      public Map<String, Object> getProperties();
   }

   public class Application implements ApplicationInt {
      ...

   }

-Ron Sigal