Why @Autowired(required=false) do not work on @Configuration beans?

Question

Let explain with an example:

Having this bean:

public class Foo {
    private String name;

    Foo(String name) {
        this.name = name;
    }

    public String getName() {
        return this.name;
    }
}

And this service:

public class FooService {
    private Foo foo;

    FooService(Foo foo) {
        this.foo = foo;
    }

    Foo getFoo() {
        return this.foo;
    }
}

Given the following Spring configuration:

@Configuration
public class SpringContext {
//    @Bean
//    Foo foo() {
//        return new Foo("foo");
//    }

    @Bean
    @Autowired(required = false)
    FooService fooService(Foo foo) {
        if (foo == null) {
            return new FooService(new Foo("foo"));
        }
        return new FooService(foo);
    }
}

For completeness here is a simple unit test:

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(classes = {SpringContext.class})
public class SpringAppTests {
    @Autowired
    private FooService fooService;

    @Test
    public void testGetName() {
        Assert.assertEquals("foo", fooService.getFoo().getName());
    }
}

Then loading the context will throw a NoSuchBeanDefinitionException (Foo).

Can anyone see anything wrong/missing on this example, or provide me a reason for that?

Thank you! Christian

Answer 1

In addition to the other answers:

The problem is that spring does not take the required=false into account when injecting parameters. See ConstructorResolver

return this.beanFactory.resolveDependency(
        new DependencyDescriptor(param, true), beanName, autowiredBeanNames, typeConverter);

The second argument is always true:

public DependencyDescriptor(MethodParameter methodParameter, boolean required)

EDIT: Spring uses the ConstructorResolver for

• "real" constuctor injection

  @Autowired(required=false) // required=false WILL NOT WORK
  public FooService(Foo foo){
      ...
  }
  

• factory methods

  @Bean
  @Autowired(required=false) // required=false WILL NOT WORK
  FooService fooService(Foo foo) {
       if (foo == null) {
           return new FooService(new Foo("foo"));
       }
       return new FooService(foo);
  }
  

Thus in both cases the required attribute is ignored.

Answer 2

You have your syntax wrong. The @Autowired(required = false) would need to be relating to the Foo.

For example:

@Configuration
public class SpringContext {

    @Autowired(required = false)
    private Foo foo;

    @Bean
    FooService fooService() {
        if (foo == null) {
            return new FooService(new Foo("foo"));
        }
        return new FooService(foo);
    }
}

Answer 3

required=false does work on @Configuration beans, however, the @Autowired annotation should be placed along with the constructor argument. This is the correct syntax:

@Bean
Test1 test1(@Autowired(required = false) Test2 test2){
    return new Test1(test2);
}

Answer 4

Try

@Configuration
public class SpringContext {
//    @Bean
//    Foo foo() {
//        return new Foo("foo");
//    }

    @Autowired(required = false)
    Foo foo;

    @Bean    
    FooService fooService() {
        if (this.foo == null) {
            return new FooService(new Foo("foo"));
        }
        return new FooService(this.foo);
    }
}