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Overriding Tapestry IoC Services

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In most cases, services are injected by matching just the type; there is no @InjectService annotation, just a method or constructor parameter whose type matches the service's interface.

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:

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

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In this example, we are using addInstance() which will instantiate the indicated class and handle dependency resolution Footnote. (Be careful with this, because in some cases, resolving dependencies of the override class can require checking against the ServiceOverrides service, and you'll get a runtime exception about ServiceOverrides requiring itself!).

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

  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);
  }

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

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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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 display

 -footnotes

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