Check, if a scoped bean is null

Question

In my Java-Configuration in Spring I have a bean, that is annotated as follows:

@Bean
@Scope(value = "request", proxyMode = ScopedProxyMode.INTERFACES)
public Object foo() { ... }

This method sometimes returns a null (if there is nothing to instanciate). In my code, I would like to check for this case like:

@Inject
Object foo

if (foo != null)
   foo.be_wise();

But this does not work, because foo is proxied and, hence, is never null! So, the only way to check for the null I could find is to trigger the NullPointerException like this:

try
{
  foo.dont_be_wise();
}
catch (NullPointerException e)
{
  be_wise();
}

I do not like that, because throwing exceptions is costly!

Is there another way to check the proxied bean for null?

Answer 1

This might work for retrieving the proxied instance. In Spring 4.2.4, this works for @Autowired -injected beans, which I think is basically the same thing.

((org.springframework.aop.framework.Advised) foo).getTargetSource().getTarget()

Answer 2

Support for unwrapping proxies has been added to the spring-test module (Spring 4.2.4). See the related commit https://github.com/spring-projects/spring-framework/commit/efe3a35da871a7ef34148dfb65d6a96cac1fccb9

Slightly modified example (see also AopUtils ):

if (AopUtils.isAopProxy(myBean) && (myBean instanceof Advised)) {
     MyFoo target ((Advised) myBean).getTargetSource().getTarget();
     if (target != null) {
         // ...
     }
}

Although this is a way to go there are alternative (and probably more elegant ways) to solve the problem:

Null Object

Introducing a NoOp implementation of your interface abstracts the null-ckecks away from your client code. See Null Object Design Pattern . In this case your @Bean method would never return null .

Conditional Bean Registration

Since Spring 4.0 beans can be instantiated on a @Conditional basis. Depending on your use-case this could be an option. See Conditionally include @Bean methods .