Retrieve a generic bean via BeanFactory.getBean(Class)

Question

With Spring 4.x I can easily autowire a generic bean and have Spring find it safely, even if the container bean is generic.

E.g. the following work (see also)

class MyBean {

    @Autowired
    private Dao<Entity> dao;

}

class MyBean<T> {

    @Autowired
    private Dao<T> dao;

}

However I sometimes need to retrieve beans at runtime during method execution instead of relying on autowiring (e.g. the beans may not be ready yet during context initialization)

private myCode() {

    BeanFactory beanFactory; //or ConfigurableListableBeanFactory too

    Dao<Entity> dao = beanFactory.getBean(....????....);
}

Considerations:

BeanFactory.getBean accepts a bean name and/or a type argument. I could or could not know the bean's name at runtime
Dao.class resolves to any generic implementation of Dao (e.g. Dao and Dao)

Questions is:

How do I invoke BeanFactory to get a bean instance that is bound to a given type?

Related: I know that Spring's RestTemplate requires a ParameterizedTypeReference when you need to bind a call to a return type of List<T> (when you know T)

score 5 · Accepted Answer · answered Dec 11 '17 at 11:36

5

The following workaround works. However I will NOT accept my answer because the workaround lacks readability and is affected by an unchecked cast

String[] names = beanFactory.getBeanNamesForType(ResolvableType.forClassWithGenerics(Dao.class, Entity.class));
Dao<Entity> dao = beanFactory.getBean(names[0], Dao.class);

Rationale: Spring allows to get bean names for a parameterized type. Under the assumption that the first call returns only one result, the second works by returning that bean. Unfortunately, the second call generates a compiler time warning

answered Dec 11 '17 at 11:36

usr-local-ΕΨΗΕΛΩΝ

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Accepted for lack of better answers – usr-local-ΕΨΗΕΛΩΝ Sep 05 '19 at 20:27
Works fine, +1. Seems no better alternatives exists. – Woland Nov 01 '19 at 06:55
Good job but yeah pity... at some point I would prefer code duplication with explicit types over voodoo and circumvent this altogether. – html_programmer Aug 27 '21 at 09:38

score 3 · Answer 2 · answered Sep 16 '20 at 16:41

Since Spring version 4.X.X you simply autowire the ApplicationContext as it now implements the BeanFactory interface. Example:

@Component     
public class BeanUtil {

    @Autowired
    private ApplicationContext applicationContext;     
    
    public Parent get() {
        ResolvableType resolvableType = ResolvableType.forClassWithGenerics(Parent.class, ResolvableType.forClass(Child.class));
        String[] beanNames = applicationContext.getBeanNamesForType(resolvableType);
        assert beanNames.length == 1;
        String beanName = beanNames[0];
        Parent parent = applicationContext.getBean(beanName, Parent.class);
        return parent;
    }         

}

Retrieve a generic bean via BeanFactory.getBean(Class)

How do I invoke BeanFactory to get a bean instance that is bound to a given type?

2 Answers2