How to add bean programmatically to Spring context?

Question

I would like to create custom child context from some configuration and additionally add some beans to it programmatically.

I read answer https://stackoverflow.com/a/4540762/258483 about BeanDefinitionRegistryPostProcessor but don't understand how to use it. If I write implementation of BeanDefinitionRegistryPostProcessor then what to do with it next? Add to context? But this is the question: how to add bean to context! If I would be able to add BeanDefinitionRegistryPostProcessor to context, then why I would ask how to add beans?

The problem is that I have context and want to add bean to it.

I know I can instantiate beans and autowire them with

Context#getAutowireCapableBeanFactory().createBean(klass);

but this apparently just wires class, but not adds it to context?

Answer 1

From Spring 5.0 onwards, you can register your beans dynamically directly using the GenericApplicationContext.

GenericApplicationContext ac = ....;
// example
ac.registerBean("myspecialBean", Integer.class, () -> new Integer(100));
// using BeanDefinitionCustomizer
ac.registerBean("myLazySpecialBean", Integer.class, () -> new Integer(100), (bd) -> bd.setLazyInit(true));

See the javadoc here for different APIs for registerBean

Answer 2

Originally answered here by myself, repeating it here as well.

Actually AnnotationConfigApplicationContext derived from AbstractApplicationContext, which has empty postProcessBeanFactory method left for override

/**
 * Modify the application context's internal bean factory after its standard
 * initialization. All bean definitions will have been loaded, but no beans
 * will have been instantiated yet. This allows for registering special
 * BeanPostProcessors etc in certain ApplicationContext implementations.
 * @param beanFactory the bean factory used by the application context
 */
protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
}

To leverage this, Create AnnotationConfigApplicationContextProvider class which may look like following(given for Vertx instance example, you can use MyClass instead)...

public class CustomAnnotationApplicationContextProvider {
private final Vertx vertx;

public CustomAnnotationApplicationContextProvider(Vertx vertx) {
    this.vertx = vertx;
}

/**
 * Register all beans to spring bean factory
 *
 * @param beanFactory, spring bean factory to register your instances
 */
private void configureBeans(ConfigurableListableBeanFactory beanFactory) {
    beanFactory.registerSingleton("vertx", vertx);
}

/**
 * Proxy method to create {@link AnnotationConfigApplicationContext} instance with no params
 *
 * @return {@link AnnotationConfigApplicationContext} instance
 */
public AnnotationConfigApplicationContext get() {
    return new AnnotationConfigApplicationContext() {

        @Override
        protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
            super.postProcessBeanFactory(beanFactory);
            configureBeans(beanFactory);
        }
    };
}

/**
 * Proxy method to call {@link AnnotationConfigApplicationContext#AnnotationConfigApplicationContext(DefaultListableBeanFactory)} with our logic
 *
 * @param beanFactory bean factory for spring
 * @return
 * @see AnnotationConfigApplicationContext#AnnotationConfigApplicationContext(DefaultListableBeanFactory)
 */
public AnnotationConfigApplicationContext get(DefaultListableBeanFactory beanFactory) {
    return new AnnotationConfigApplicationContext(beanFactory) {

        @Override
        protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
            super.postProcessBeanFactory(beanFactory);
            configureBeans(beanFactory);
        }
    };
}

/**
 * Proxy method to call {@link AnnotationConfigApplicationContext#AnnotationConfigApplicationContext(Class[])} with our logic
 *
 * @param annotatedClasses, set of annotated classes for spring
 * @return
 * @see AnnotationConfigApplicationContext#AnnotationConfigApplicationContext(Class[])
 */
public AnnotationConfigApplicationContext get(Class<?>... annotatedClasses) {
    return new AnnotationConfigApplicationContext(annotatedClasses) {

        @Override
        protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
            super.postProcessBeanFactory(beanFactory);
            configureBeans(beanFactory);
        }
    };
}

/**
 * proxy method to call {@link AnnotationConfigApplicationContext#AnnotationConfigApplicationContext(String...)} with our logic
 *
 * @param basePackages set of base packages for spring
 * @return
 * @see AnnotationConfigApplicationContext#AnnotationConfigApplicationContext(String...)
 */
public AnnotationConfigApplicationContext get(String... basePackages) {
    return new AnnotationConfigApplicationContext(basePackages) {

        @Override
        protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
            super.postProcessBeanFactory(beanFactory);
            configureBeans(beanFactory);
        }
    };
}
}

While creating ApplicationContext you can create it using

Vertx vertx = ...; // either create or for vertx, it'll be passed to main verticle
ApplicationContext context = new CustomAnnotationApplicationContextProvider(vertx).get(ApplicationSpringConfig.class);

Answer 3

I'm using this in my current application, because I already have an object that I want to register. I can have applicationContext injected as a bean.

private void registerAsBean(
  ApplicationContext injectedApplicationContext, 
  MyClass objectToRegisterAsBean, 
  String beanName) {

    AutowireCapableBeanFactory beanFactory = 
      injectedApplicationContext.getAutowireCapableBeanFactory();
    beanFactory.initializeBean(objectToRegisterAsBean, beanName);
}