如何在SpringAutowire泛型类型的Bean？

Question

@Configuration
public class AppConfig {

    @Bean
    public Item<String> stringItem() {
        return new StringItem();
    }

    @Bean
    public Item<Integer> integerItem() {
        return new IntegerItem();
    }

}

但是当我尝试@autowire item 时，我会遇到以下异常。

"No qualifying bean of type [Item] is defined: expected single matching bean but found 2: stringItem, integerItem"

我应该如何在Spring中Autowire泛型类型item ？

Answer 1

简单的解决方案是升级到Spring4.0，因为它会自动将泛型视为@qualifier的一种形式，如下所示：

@Autowired
private Item<String> strItem; // Injects the stringItem bean

@Autowired
private Item<Integer> intItem; // Injects the integerItem bean

事实上，在将嵌套泛型注入列表时，您甚至可以autowire嵌套泛型，如下所示：

// Inject all Item beans as long as they have an <Integer> generic
// Item<String> beans will not appear in this list
@Autowired
private List<Item<Integer>> intItems;

这是怎么运作的？

// Assuming 'field' refers to 'intItems' above
ResolvableType t1 = ResolvableType.forField(field); // List<Item<Integer>> 
ResolvableType t2 = t1.getGeneric(); // Item<Integer>
ResolvableType t3 = t2.getGeneric(); // Integer
Class<?> c = t3.resolve(); // Integer.class

// or more succinctly
Class<?> c = ResolvableType.forField(field).resolveGeneric(0, 0);

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