Red Hat
Sep 14, 2015
by Martin Kouba

Recently released JDK 8u60 has revealed a problem in Weld where not all synthetic members were ignored correctly. This has been fixed in 2.2.16.Final, 2.3.0.CR2 and 3.0.0.Alpha14 (not released yet). However, if not using a lambda referencing an event/disposed parameter inside an observer/disposer method, your application is most probably not affected. See also the related issue - WELD-2019.

Use case

If there is a lambda referencing an event/disposed parameter inside an observer/disposer method, the compiler creates a synthetic method with the event parameter as one of the method parameters. Since 8u60 the parameter annotations are preserved even for the synthetic method. And so Weld incorrectly recognizes these synthetic methods as observer/disposer methods.

Symptoms

You may get WELD-000409: Observer method for container lifecycle event can only…​ if using such a lambda in an extension or even WELD-001408 Unsatisfied dependencies for type…​ if using such a lambda in a regular observer and the lambda is using more references (i.e. not only event/disposed parameter) - these are also the method parameters of the synthetic method, and in CDI these additional parameters are injection points.

Example

class Foo {
        void observe(@Observes @Juicy String payload) {
          Arrays.asList("foo").stream().filter((s) -> s.equals(payload));
        }
      }

A synthetic method is created for the lambda and the event parameter is passed as a method parameter. The annotations are preserved. As a result Weld creates two observer methods having the same event parameter: @Observes @Juicy String payload.

Workaround

Instead of the event parameter reference use an additional local variable with the same value assigned:

public void observe(@Observes @Juicy String payload) {
         String p = payload;
         Arrays.asList("foo").stream().filter((s) -> s.equals(p));
      }
Original Post