[infinispan-dev] Cluster Listeners 7.0.0.Alpha1

[William Burns]

The way Listeners work they are only half typed, which is unfortunate.
 It determines what method to invoke solely on annotations, so
Listener methods can define any type for the Event that they want.
The developer using a Converter would have to be cognizant that they
should be the same or super type for the listener they use.
Specifically CacheEntryEvent<K, V> the type V must match or be a super
type of C defined on the Converter<K, V, C> if a converter is
provided, but there are no compile checks for this :(

Eg.

   @Listener
   class SomeListener {
      @CacheEntryCreated
      public void handleEvent(CacheEntryEvent<String, Integer> event) {
         ....
      }
   }

   SomeListener listener = ...
   Converter<String, String, Integer> converter = ...
   cache.addListener(listener, null, converter);

So a user may get a ClassCastException at runtime if they retrieve
those keys or values and they don't match.



The only types that are specifically checked are the Key/Value types
on both the KeyValueFilter and the Converter class and will throw a
checked exception if they don't match.

This example will have a checked exception, since we verify the types
for those.  Note the Filter has a type String for V but the Converter
has Integer for V.

Eg:

  KeyValueFilter<String, String> filter ..
  Converter<String, Integer, Integer> converter ...
  cache.addListener(listener, filter, converter);


One thing this made me think of though is that we don't match the
Cache variants with the filter and converter, this should be doable to
enhance the hierarchy to ensure those types match the cache as well,
but it might take a bit of refactoring to get it right.  I have logged
[1] to fix this.

[1] https://issues.jboss.org/browse/ISPN-4079

On Thu, Mar 6, 2014 at 10:02 AM, Vladimir Blagojevic
<vblagoje at redhat.com> wrote:
> Very cool stuff Will! Just to clarify, one could define clustered
> listener, filter and converter and tie them all up together. Such a
> listener will be invoked when filter criteria is met, and converter
> converts key/value to some C object which is then sent of to listener,
> right? So how do you define method on listener to be invoked with
> converted object C as a parameter?
>
>
> On 3/5/2014, 10:02 AM, William Burns wrote:
>> Hello everyone,
>>
>> I am happy to announce that the latest Infinispan 7.0.0.Alpha1 build
>> has the first pass of Cluster Listeners implemented.
>>
>> You can read all about the details at the blog post [1].
>>
>> You can get the latest build of Infinispan from our site [2].
>>
>> Try it out and let us know what you guys think.
>>
>> Happy listening!
>>
>>   - Will
>>
>>
>> [1] http://blog.infinispan.org/2014/03/embedded-cluster-listeners-in.html
>> [2] http://infinispan.org/download/
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