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Overriding Tapestry IoC Services

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In this case, it is very easy to supply your own alternate implementation of a service, by contributing a Service Override in your module class (usually AppModule.java), like this:

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  @Contribute(ServiceOverride.class)
  public static void setupApplicationServiceOverrides(MappedConfiguration<Class,Object> configuration)
  {
    configuration.addInstance(SomeServiceType.class, SomeServiceTypeOverrideImpl.class);
  }

The name of the method is not important, as long as the @Contribute annotation is present on the method.

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Sometimes you'll want to define the override as a service of its own. This is useful if you want to inject a Logger specific to the service, or if the overriding implementation needs a service configuration:

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  public static void bind(ServiceBinder binder)
  {
    binder.bind(SomeServiceType.class, SomeServiceTypeOverrideImpl.class).withId("SomeServiceTypeOverride");
  }

  @Contribute(ServiceOverride.class)
  public static void setupApplicationServiceOverrides(MappedConfiguration<Class,Object> configuration, @Local SomeServiceType override)
  {
    configuration.add(SomeServiceType.class, override);
  }

Here we're defining a service using the module's bind() method.

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Alternately, this approach is useful to override a service that is matched using marker annotations.

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  public SomeServiceType decorateSomeServiceType(final SomeServiceType delegate)
  {
    return new SomeServiceType() { . . . };
  }

This decorate method is invoked because its name matches the service id of the original service, "SomeServiceType" (you have to adjust the name to match the service id).

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Note that the object passed in as delegate may be the core service implementation, or it may be some other interceptor from some other decorator for the same service.

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