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Subject: Re: AsyncListeners and resource injection
From: David Jencks <david_jencks@yahoo.com>
In-Reply-To: <015C21FF-AC6C-4EF0-90C3-29F76E12E549@yahoo.com>
Date: Thu, 16 Sep 2010 13:26:29 -0700
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 <015C21FF-AC6C-4EF0-90C3-29F76E12E549@yahoo.com>
To: "Tomcat Developers List" <dev@tomcat.apache.org>


On Sep 15, 2010, at 10:51 PM, David Jencks wrote:

>=20
> On Sep 15, 2010, at 9:58 PM, David Jencks wrote:
>=20
>> I think this is how AsyncContextImpl creates async listeners (lines =
228ff)
>>=20
>>   @Override
>>   public <T extends AsyncListener> T createListener(Class<T> clazz)
>>           throws ServletException {
>>       T listener =3D null;
>>       try {
>>            listener =3D clazz.newInstance();
>>       } catch (InstantiationException e) {
>>           ServletException se =3D new ServletException(e);
>>           throw se;
>>       } catch (IllegalAccessException e) {
>>           ServletException se =3D new ServletException(e);
>>           throw se;
>>       }
>>       return listener;
>>   }
>>=20
>>=20
>>=20
>> but the 3.0 spec section 15.5 page 179 says
>>=20
>> Annotations must be supported on the following container managed =
classes that implement the following interfaces and are declared in the =
web application deployment descriptor or using the annotations defined =
in Section 8.1, =93Annotations and pluggability=94 on page 8-61 or added =
programmatically.
>>=20
>> and includes AsyncListener in the table following. =20
>>=20
>> So shouldn't this be using the instance manager to create the =
instance so the resource injection machinery can do its stuff?
>>=20
>>=20
>> Secondly, if you do try to register an AsyncListener with  the =
ServletContext so it can be scanned for annotations, aside from not =
actually scanning it, it quickly gets to this code (ApplicationContext =
lines 1262 ff)
>>=20
>>   @Override
>>   public <T extends EventListener> void addListener(T t) {
>>       if (!context.getState().equals(LifecycleState.STARTING_PREP)) {
>>           throw new IllegalStateException(
>>                   sm.getString("applicationContext.addListener.ise",
>>                           getContextPath()));
>>       }
>>=20
>>       // TODO SERVLET3
>>       // throw UnsupportedOperationException - if this context was =
passed to the
>>       // {@link =
ServletContextListener#contextInitialized(javax.servlet.ServletContextEven=
t)}
>>       // method of a {@link ServletContextListener} that was not =
declared
>>       // in web.xml, a web-fragment or annotated with {@link =
WebListener}.
>>=20
>>       boolean match =3D false;
>>       if (t instanceof ServletContextAttributeListener ||
>>               t instanceof ServletRequestListener ||
>>               t instanceof ServletRequestAttributeListener ||
>>               t instanceof HttpSessionAttributeListener) {
>>           context.addApplicationEventListener(t);
>>           match =3D true;
>>       }
>>=20
>>       if (t instanceof HttpSessionListener
>>               || (t instanceof ServletContextListener &&
>>                       newServletContextListenerAllowed)) {
>>           context.addApplicationLifecycleListener(t);
>>           match =3D true;
>>       }
>>=20
>>       if (match) return;
>>=20
>>       throw new IllegalArgumentException(sm.getString(
>>               "applicationContext.addListener.iae.wrongType",
>>               t.getClass().getName()));
>>=20
>>   }
>>=20
>>=20
>> which doesn't accept AsyncListeners.  (of course it shouldn't do =
anything with then).
>>=20
>> Thoughts?
>>=20
>> thanks
>> david jencks
>>=20
>=20
> BTW I opened bug 49937 with  fixes that work for me for these =
problems.
>=20
> david jencks
>=20

The situation seems to be more complicated than I thought at first.

As noted above, section 15.5 clearly indicates annotation based resource =
injection is supported for all servlet related listeners including =
AsyncListener, and that these can be specified in the xml deployment =
descriptor, via annotation, or by adding programatically.

However....=20

4.4.3 indicates that an AsyncListener cannot be added programatically

4.4.3.5 indicates that resource injection is not supported for listeners =
added programatically unless the listener is a managed bean.  I think =
this directly contradicts 15.5.

8.1.4 indicates that an AsyncListener cannot be annotated with =
@WebListener

11.3.2 says

Listener classes are declared in the Web application deployment =
descriptor using the listener element. They are listed by class name in =
the order in which they are to be invoked. Unlike other listeners, =
listeners of type AsyncListener may only be registered (with a =
ServletRequest) programmatically.

I can't figure out what this is supposed to mean.  It might mean that =
you aren't allowed to list an AsyncListener in your web.xml, or it might =
mean that you can, but to use it you have to explicitly add it to an =
AsyncContext.

Despite the contradictions in the spec, it seems pretty clear that an =
asyncListener can be a managed bean and thus be subject to resource =
injection.  It might also be possible for it to be listed in web.xml, =
have a @WebListener annotation, and be "added" programatically so it can =
be scanned for normal ee resource injection annotations (depending on =
how much weight you put on 15.5 compared with the other sections).  So, =
I think that the AsyncContext.createListener method should use the =
instance manager in any case.  I think it makes sense to relax the =
restrictions on @WebListener and programatically adding AsyncListeners =
as well (i.e. giving priority to 15.5 rather than all the other =
sections) since it doesn't break anything and is more powerful.

thanks
david jencks


>=20
>>=20
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>>=20
>=20
>=20
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>=20


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