Creating beans with BeanFactoryPostProcessor

Question

Spring BeanFactoryPostProcessor problem

I want to create a Spring BeanFactoryPostProcessor that add beans to the current ApplicationContext.

I have a lot of Web-Services definition in my spring-ws-config.xml and I want to reduce as much as possible.

XML Configuration

The configuration looks like:

<bean id="menu"
    class="org.springframework.ws.wsdl.wsdl11.DefaultWsdl11Definition"
    lazy-init="true">
    <property name="schemaCollection">
        <bean
            class="org.springframework.xml.xsd.commons.CommonsXsdSchemaCollection">
            <property name="inline" value="true" />
            <property name="xsds">
                <list>
                    <value>classpath:xsd.xsd</value>
                </list>
            </property>
        </bean>
    </property>
    <property name="portTypeName" value="portType" />
    <property name="serviceName" value="serviceName" />
    <property name="locationUri" value="/endpoints" />
</bean>

Java Configuration

So, I create a @Configuration class with the following bean definition:

@Bean
@Lazy
public DefaultWsdl11Definition webService() throws IOException {

    logger.info("Creating Web Service");
    DefaultWsdl11Definition toRet = new DefaultWsdl11Definition();
    toRet.setPortTypeName("portType");
    toRet.setServiceName("serviceName");

    CommonsXsdSchemaCollection collection = new CommonsXsdSchemaCollection();
    collection.setInline(true);
    collection.setXsds(new Resource[] { new ClassPathResource("path1") });
    collection.afterPropertiesSet();

    toRet.setSchemaCollection(collection);
    toRet.setLocationUri("/endpoints");
    return toRet;

}

This is much better!, but I want to reduce it more, so I want to create a annotation called @WebServiceDefinition, and add a BeanFactoryPostProcessor to create the beans automatically, so I wrote this:

BeanFactoryPostProcessor

@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory bf)
        throws BeansException {

    Map<String, Object> beans = bf.getBeansWithAnnotation(WebService.class);

    for (Entry<String, Object> entry : beans.entrySet()) {
        Object bean = entry.getValue();
        WebService ws = bean.getClass().getAnnotation(WebService.class);
        String name = getName(entry.getKey());
        DefaultWsdl11Definition newWS = createWebService(name, ws.xsds());

        bf.registerSingleton(name, newWS);
    }
}

But, this doesn't works!, I wrote a simple test, you can see it here

I see that the IOC don't work with the classes with the annotations, this is because the method: BeanFactory#getBeansWithAnnotation don't initialize it, mark it as created, and dont inject anything.

Workaround

I do a workaround: get all beans by name, get the corresponde class and use #bf.getBeansOfType(Class), (this method dont initialize it!).

My questions:

• This is a valid workaround?
• How I can use the method #getBeansWithAnnotation() and don't initialize the bean?

Answer 1

The problem is that the BeanFactoryPostProcessor can't work with instances, and the #getBeansWithAnnotation() returns instances, so, it is not recommended, here the relevant Javadoc:

A BeanFactoryPostProcessor may interact with and modify bean definitions, but never bean instances. Doing so may cause premature bean instantiation, violating the container and causing unintended side-effects. If bean instance interaction is required, consider implementing BeanPostProcessor instead.

So my solution is this:

@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory bf)
        throws BeansException {

    String[] beans = bf.getBeanDefinitionNames();
    for (String s : beans) {
        Class<?> beanType = bf.getType(s);
        WebService ws = AnnotationUtils.findAnnotation(beanType,
                WebService.class);
        if (ws != null) {
            String name = getName(s);
            DefaultWsdl11Definition newWS = createWebService(name,
                    ws.xsds());

            bf.registerSingleton(name, newWS);
        }
    }

}

Answer 2

The above pattern is what I've always used. However, Spring 4 now has the method ListableBeanFactory::getBeanNamesForAnnotation which would seem to offer the same functionality.

From the javadoc:

Find all names of beans whose {@code Class} has the supplied {@link Annotation} type, without creating any bean instances yet.

Update: unfortunately this method also seems to instanciate certain (factory) beans, which in my case caused problems with @Resource injection in my processed beans.

Answer 3

I had some success with following way:

@Bean
public BeanFactoryPostProcessor beanFactoryPostProcessor() {
    return bf -> {
        BeanDefinitionRegistry beanFactory = (BeanDefinitionRegistry) bf;
        IntStream.range(0, 10).forEach(i ->
                beanFactory.registerBeanDefinition(String.format("bean-name-%d", i),
                        createCustomBeanDefinition()));
    };
}

private BeanDefinition createCustomBeanDefinition() {
    return BeanDefinitionBuilder.genericBeanDefinition(MyBeanClass.class)
            .setFactoryMethodOnBean("create", "myFactory")
            .getBeanDefinition();
}

Especially the part about factory helped me because the bean was not so simple to instantiate so I could create a factory, initialize it and then use it to create instances.

Another important point to note is that using beanFactory.registerSingleton(name, newWS); means Spring won't call its init/destroy methods, won't autowire etc. Whereas with bean definition it should do all it normally does.

And one more thing. I struggled a bit on getting properties from application.properties hooked into the BeanFactoryPostProcessor. Turns out you can autowire org.springframework.core.env.Environment which is ready at that stage of context loading and call:

Integer numberOfBeans = environment.getRequiredProperty("myApp.numberOfBeans", 
                           Integer.class);