How to bind method interceptor to provider?

Question

Is there way to bind a method interceptor to a provider rather than an instance?

e.g. I use the code below to bind interceptors how would I bind INTERCEPTOR to a provider and then to the annotation?

bindInterceptor(
    Matchers.any(), Matchers.annotatedWith(ANNOTATION.class), new INTERCEPTOR());

Answer 1

Guice does not allow AOP on instances not built by Guice: Guice AOP Limitations

"Instances must be created by Guice by an @Inject-annotated or no-argument constructor"

This means that instances created with a provider will not be candidates for AOP.

On the flip side, as long as your Provider is instantiated by Guice under the conditions mentioned, your Provider may be a candidate for AOP.

Here's an example that demonstrates this:

AOP Annotation:

@Retention(RetentionPolicy.RUNTIME) @Target(ElementType.METHOD)
@interface AOPExample {}

Provider:

public class ExampleProvider implements Provider<Example> {

    @AOPExample
    public Example get() {
        System.out.println("Building...");
        return new Example();
    }
}

Target Example:

public class Example {

    @AOPExample
    public void tryMe() {
        System.out.println("example working...");
        try {
            Thread.sleep(1000L);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

}

Module:

public class ExampleModule extends AbstractModule {
    @Override
    protected void configure() {
        bindInterceptor(Matchers.any(), Matchers.annotatedWith(AOPExample.class), new LoggingAOP());

        bind(Example.class).toProvider(ExampleProvider.class);
    }
}

Test Code:

public class Test {

    public static void main(String[] args) {
        Injector injector = Guice.createInjector(new TestModule());

        ExampleProvider exampleProvider = injector.getInstance(ExampleProvider.class);
        Example example = exampleProvider.get();

        example.tryMe();

        Example directExample = injector.getInstance(Example.class);

        directExample.tryMe();

    }
}

Test Output:

start
Building...
end took: 3
example working...
start
Building...
end took: 0
example working...

Notice that the "example working..." is not surrounded by the timer code. The Provider.get ("Building...") is however.

If your question is: can the interceptor (new INTERCEPTOR()) be provided through a Guice Provider, the answer is no. The closest you may get to this functionality is calling the requestInjection() in the module configure method. This will inject your Interceptor with the appropriate code. From your interceptor you may be able to use Providers to avoid any sort of overhead that is causing you slowness during startup.

Here's what I mean:

Module:

public class TestModule extends AbstractModule {
    @Override
    protected void configure() {
        bind(String.class).toInstance("One");
        bind(String.class).annotatedWith(Names.named("two")).toInstance("Two");

        LoggingAOP loggingAOP = new LoggingAOP();

        bindInterceptor(Matchers.any(), Matchers.annotatedWith(AOPExample.class), loggingAOP);

        requestInjection(loggingAOP);

        bind(Example.class).toProvider(ExampleProvider.class);
    }
}

Interceptor:

public class LoggingAOP implements MethodInterceptor {

    @Inject
    private Provider<SomethingThatTakesALongTimeToInit> provider;

    public Object invoke(MethodInvocation invocation) throws Throwable {
        provider.get()...
        System.out.println("start");
        long start = System.currentTimeMillis();
        Object value =  invocation.proceed();
        System.out.println("end took: " + (System.currentTimeMillis() - start));
        return value;
    }
}

Hope this answers your question.