Spring：没有限定符的 Autowire bean

Question

是否可以在 spring 中自动装配没有给定限定符的 bean？用例是拥有所有 bean 的列表，但排除一个：

@Autowired
@NotQualifier("excludedBean")    // <-- can we do something like this?
List<SomeBean> someBeanList;


public class Bean1 implements SomeBean {}

public class Bean2 implements SomeBean {}

@Qualifier("excludedBean")
public class Bean3 implements SomeBean {}

在上面的例子中someList应该包含一个Bean1andBean2但不是的实例Bean3。

（备注：我知道相反的方法会起作用，即向Bean1and添加一些限定符Bean2，然后使用该限定符自动装配。）

编辑：一些进一步的说明：

• 所有 bean 都在 spring 上下文中（也被排除在外）。
• 配置需要基于注解，而不是基于 xml。因此，例如关闭 autowired-candidate不起作用。
• bean 的自动装配能力必须保持一般。换句话说，我想从注入点中排除 bean List<SomeBean> someBeanList;，但我想在其他地方自动装配它。

Answer 1

您可以使用元注释来引入您自己的@Conditional注释@Qualifier

@Target({ElementType.FIELD, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Qualifier
@Conditional(MyCondition.class)
public @interface ExcludeBean {

然后引入可以执行条件逻辑的类

public class MyCondition implements Condition {

    @Override
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        return !metadata.equals(ExcludeBean.class);
    }

}

在您的配置类中

  @Bean
  @ExcludeBean
  public BeanA beanA() {
      return new BeanA();
  }

autowire-candidate您还可以通过对特定 bean进行设置或指定来将 bean 排除在自动装配候选对象之外default-autowire-candidates="list of candidates here"

Answer 2

要点是它的排除 bean 是在上下文中，但没有注入到某些具有排除条件的情况中。

您可以使用自定义注释和 BeanPostProcessor 来排除带有限定符的 bean。（我做了简单案例的示例，用于 bean 类型的集合，但您可以扩展它）

排除的注释：

@Component
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface ExcludeBeanByQualifierForCollectionAutowired {

    String qualifierToExcludeValue();

    Class<?> aClass();
}

带注入的 Bean 后处理器

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.stereotype.Component;

import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.Collection;

@Component
public class ExcludeAutowiredBeanPostProcessor implements BeanPostProcessor {

    @Autowired
    private ConfigurableListableBeanFactory configurableBeanFactory;

    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) {
        Field[] fields = bean.getClass().getDeclaredFields();
        for (Field field : fields) {
            field.setAccessible(true);
            ExcludeBeanByQualifierForCollectionAutowired myAutowiredExcludeAnnotation = field.getAnnotation(ExcludeBeanByQualifierForCollectionAutowired.class);
            if (myAutowiredExcludeAnnotation != null) {

                Collection<Object> beanForInjection = new ArrayList<>();

                String[] beanNamesOfType = configurableBeanFactory.getBeanNamesForType(myAutowiredExcludeAnnotation.aClass());
                for (String injectedCandidateBeanName : beanNamesOfType) {

                    Object beanCandidate = configurableBeanFactory.getBean(injectedCandidateBeanName);

                    Qualifier qualifierForBeanCandidate = beanCandidate.getClass().getDeclaredAnnotation(Qualifier.class);

                    if (qualifierForBeanCandidate == null || !qualifierForBeanCandidate.value().equals(myAutowiredExcludeAnnotation.qualifierToExcludeValue())) {
                        beanForInjection.add(beanCandidate);
                    }
                }
                try {
                    field.set(bean, beanForInjection);
                } catch (IllegalAccessException e) {
                    e.printStackTrace();
                }
            }
        }

        return bean;
    }


    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) {
        return bean;
    }
}

和例子：

public class ParentBean {}

public class Bean1Included extends ParentBean {}

public class Bean2Included extends ParentBean {}

public class Bean3Included extends ParentBean {}

@Qualifier("excludedBean")
public class BeanExcluded extends ParentBean {}

配置

@Configuration
public class BeanConfiguration {

    @Bean
    public Bean1Included getBean1(){
        return new Bean1Included();
    }

    @Bean
    public Bean2Included getBean2(){
        return new Bean2Included();
    }

    @Bean
    public Bean3Included getBean3(){
        return new Bean3Included();
    }

    @Bean
    public BeanExcluded getExcludedBean(){
        return new BeanExcluded();
    }

    @Bean
    public ExcludeAutowiredBeanPostProcessor excludeAutowiredBeanPostProcessor(){
        return new ExcludeAutowiredBeanPostProcessor();
    }
}

和结果：

@ExtendWith(SpringExtension.class) // assumes Junit 5
@ContextConfiguration(classes = BeanConfiguration.class)
public class ExcludeConditionTest {

    @Autowired
    private ApplicationContext context;
    @Autowired
    private BeanExcluded beanExcluded;
    @ExcludeBeanByQualifierForCollectionAutowired(qualifierToExcludeValue = "excludedBean" , aClass = ParentBean.class)
    private List<ParentBean> beensWithoutExclude;

    @Test
    void should_not_inject_excluded_bean() {
        assertThat(context.getBeansOfType(ParentBean.class).values())
                .hasOnlyElementsOfTypes(Bean1Included.class,
                                        Bean2Included.class,
                                        Bean3Included.class,
                                        BeanExcluded.class);

        assertThat(beansWithoutExclude)
                .hasOnlyElementsOfTypes(Bean1Included.class,
                                        Bean2Included.class,
                                        Bean3Included.class)
                .doesNotHaveAnyElementsOfTypes(BeanExcluded.class);

        assertThat(beanExcluded).isNotNull();
    }
}