[FIXED] Spring-like PostProcessor Hook on Dynamically Registered Third-Party Bean

Issue

What Spring Framework hook do I use on dynamically registered third-party beans?

I have a href="https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/beans/factory/support/BeanDefinitionRegistryPostProcessor.html#postProcessBeanDefinitionRegistry-org.springframework.beans.factory.support.BeanDefinitionRegistry-" rel="nofollow noreferrer">BeanDefinitionRegistryPostProcessor that I am using to dynamically classpath-scan and instantiate multiple third-party beans (gRPC AbstractStub instances). I need to register ClientInterceptors on the stub so that the augmented AbstractStub is ready for application processing. I use dynamically-created *Stub @Beans to eliminate all the @Bean boilerplate and ensure consistent channel configurations.

Constraints

• The AbstractStub implementations are gRPC-generated classes. My classes extend AbstractStub.
• The preferred static factory method to use is the builder(Channel) method; this is what is used when manually boilerplating @Bean declarations.
• Each stub requires a Channel as a dependency. There are multiple Channel @Beans.

Attempts

I tried three approaches:

Approach 1: BeanDefinitionBuilder+ Supplier Function

BeanDefinitionBuilder.genericBeanDefinition(Class, Supplier) did not allow injecting the Channel dependency.

void registerBeanDefintion(final Class<S> clazz, final BeanDefinitionRegistry registry) {
    Supplier<S> stubSupplier = () -> {
        clazz.getConstructor({Channel.class});
        return BeanUtils.instantiateClass(constructor, null); // fails here; no Channel
    }
    BeanDefinitionBuilder builder =
        BeanDefinitionBuilder.genericBeanDefinition(clazz, stubSupplier);
    builder.addDependsOn(MANAGED_CHANNEL_BEAN_NAME);
    builder.addConstructorArgReference(MANAGED_CHANNEL_BEAN_NAME);
    registry.registerBeanDefinition(clazz.getName(), builder.getBeanDefinition());

Approach 2: BeanDefinitionBuilder with CallOption hooks

Unable to register a ClientInterceptor on a BeanDefinition.

void registerBeanDefintion(final Class<S> clazz, final BeanDefinitionRegistry registry) {
    builder.addDependsOn(MANAGED_CHANNEL_BEAN_NAME);
    builder.addConstructorArgReference(MANAGED_CHANNEL_BEAN_NAME);
    CallOptions callOptions = CallOptions.DEFAULT;
    // no hook in CallOptions to register ClientInterceptor
    registry.registerBeanDefinition(clazz.getName(), builder.getBeanDefinition());

Approach 3: postProcessBeanFactory()

postProcessBeanFactory doesn't operate on instantiated beans, so dependencies are not pre-resolved.

public void postProcessBeanFactory(ConfigurableListableBeanFactory configurableListableBeanFactory) throws BeansException {
    Iterator<String> iterator = configurableListableBeanFactory.getBeanNamesIterator();
    while (iterator.hasNext()) {
        String beanName = iterator.next();
        if (beanName.endsWith("Stub")) {
            AbstractStub stub = (AbstractStub) configurableListableBeanFactory.getBean(beanName); //fails
            stub.withInterceptors(newClientInterceptor()); // never gets executed
        }
    }
}

Solution

I was over-complicating it a bit since I had some separate modules: The solution is to use a simple BeanPostProcessor and invoke withInterceptors() for only the AbstractStub instances:

    @Override
    public Object postProcessAfterInitialization(final Object bean, final String beanName) throws BeansException {
        if (bean instanceof AbstractStub) {
            AbstractStub stub = (AbstractStub) bean;
            log.debug("modify bean '{}': add timeout client interceptor", beanName);
            ClientInterceptor timeoutClientInterceptor = this.newTimeoutClientInterceptor(stub);
            AbstractStub result = stub.withInterceptors(timeoutClientInterceptor);
            return result;
        }
        return bean;
    }

    ClientInterceptor newTimeoutClientInterceptor(final AbstractStub stub) {
        final Deadline deadline = this.getDeadlineTimeout(stub);
        return new ClientInterceptor() {
            @Override
            public <ReqT, RespT> ClientCall<ReqT, RespT> interceptCall(MethodDescriptor<ReqT, RespT> method, CallOptions callOptions, Channel next) {
                final ClientCall<ReqT, RespT> clientCall = next.newCall(method, callOptions.withDeadline(deadline));
                return new ClientInterceptors.CheckedForwardingClientCall<ReqT, RespT>(clientCall) {
                    @Override
                    protected void checkedStart(Listener<RespT> listener, Metadata metadata) {
                        log.debug("execute call with deadline {}", deadline);
                        delegate().start(listener, metadata);
                    }
                };
            }
        };
    }

Answered By - JJ Zabkar
Answer Checked By - Cary Denson (JavaFixing Admin)