Spring Autowired null if not found

Question

Default @Autowired Spring implementation throws error when bean that should be autowired is not defined. Is it possible to configure Spring, that will assign null to object instead of throwing exception?

EDIT:

I've add required=false to Autowired but it still not working properly. Thats my code:

@Autowired
private ApplicationContext applicationContext;

@Autowired(required = false)
private HelloService helloService;

public HelloController() {
    message = "Hello World";
    System.out.println("Controller constructor");
}

@RequestMapping(method = RequestMethod.GET)
public ModelAndView helloWorld() {
    ModelAndView modelAndView = new ModelAndView("hello");
    if (helloService == null) {
        System.out.println(message);
    } else {
        helloService.hello();
        BeanDefinitionRegistry factory = (BeanDefinitionRegistry) applicationContext.getAutowireCapableBeanFactory();
        factory.removeBeanDefinition("helloService");
    }
    return modelAndView;
}

In first request it's autowired, but in next request after removing bean with factory.removeBeanDefinition("helloService"), controller bean is construct again, and i get NoSuchBeanDefinitionException

EDIT2:

I've created another controller with the following body:

@Autowired(required = false)
private TestService testService;

@RequestMapping(method = RequestMethod.GET)
public ModelAndView hello() {
    ModelAndView modelAndView = new ModelAndView("hello");
    return modelAndView;
}

and it works properly - Object is null and it doesn't get error. Maybe i should use different method to remove bean from Spring context?

Stacktrace:

org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'helloService' is defined
at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBeanDefinition(DefaultListableBeanFactory.java:698) ~[spring-beans-4.2.7.RELEASE.jar:4.2.7.RELEASE]
at org.springframework.beans.factory.support.AbstractBeanFactory.getMergedLocalBeanDefinition(AbstractBeanFactory.java:1175) ~[spring-beans-4.2.7.RELEASE.jar:4.2.7.RELEASE]
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:284) ~[spring-beans-4.2.7.RELEASE.jar:4.2.7.RELEASE]
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197) ~[spring-beans-4.2.7.RELEASE.jar:4.2.7.RELEASE]
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.resolvedCachedArgument(AutowiredAnnotationBeanPostProcessor.java:508) ~[spring-beans-4.2.7.RELEASE.jar:4.2.7.RELEASE]
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.access$200(AutowiredAnnotationBeanPostProcessor.java:115) ~[spring-beans-4.2.7.RELEASE.jar:4.2.7.RELEASE]
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:538) ~[spring-beans-4.2.7.RELEASE.jar:4.2.7.RELEASE] 
...

STEPS TO REPRODUCE:

https://github.com/nowszy94/Autowired-null

Answer 1

you can disable this, by setting the required attribute to false.

@Autowired(required=false)

If Spring can’t find bean, it will leave field unset as null.

Answer 2

The problem is that AutowiredAnnotationBeanPostProcessor cache injection result. So, when you delete bean from context, this class think that this object is actually exists(see private class AutowiredFieldElement extends InjectionMetadata.InjectedElement in AutowiredAnnotationBeanPostProcessor.class and method inject).So, you should clear that cache.

The most stupid way, that i found is, but looks like that you want to do

@Controller
@RequestMapping("/hello")
public class HelloController {

    @Autowired(required = false)
    private HelloService helloService;

    @Autowired
    private ApplicationContext applicationContext;

    @RequestMapping(method = RequestMethod.GET)
    public ModelAndView modelAndView() {
        ModelAndView modelAndView = new ModelAndView("hello");
        if (helloService != null) {
            helloService.hello();
            removeBean("helloService");
        }

        return modelAndView;
    }

    private void removeBean(String beanName) {
        BeanDefinitionRegistry factory = (BeanDefinitionRegistry) applicationContext
                .getAutowireCapableBeanFactory();
        factory.removeBeanDefinition(beanName);
        clearCache(factory);
    }

    private void clearCache(BeanDefinitionRegistry beanFactory){
        AutowiredAnnotationBeanPostProcessor processor = null;

        for (BeanPostProcessor beanPostProcessor : ((DefaultListableBeanFactory) beanFactory).getBeanPostProcessors()){
            if (beanPostProcessor.getClass().equals(AutowiredAnnotationBeanPostProcessor.class)){
                processor = (AutowiredAnnotationBeanPostProcessor) beanPostProcessor;
            }
        }

        try {
            Field injectionMetadataCache = processor.getClass().getDeclaredField("injectionMetadataCache");
            injectionMetadataCache.setAccessible(true);
            Method clear = Map.class.getMethod("clear");
            clear.invoke( injectionMetadataCache.get(processor));
        } catch (NoSuchFieldException e) {
            e.printStackTrace();
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        }


    }

}