Question

@Bean
public TimedRepository timedRepository(RealRepository repo) {
    return new TimedRepository(repo, timer); // Adds some metrics
}

@Bean
public RealRepository realRepository(DataSource ds) {
    return new RealRepository(ds); // The real jdbc implementation
}

在旧的XML时代，我将真正的存储库配置为匿名内部bean。是否可以使用新的Java配置方法执行类似的操作？在timedRepository工厂方法中实例化实际存储库不是一个选项，因为我希望Spring在RealRepository上获取注释。

动机是避免任何其他bean获取真正的存储库实现。我还应该提到两个bean都实现了一个Repository接口，任何bean都可以根据存储库使用它（他们不应该知道TimedRepository或RealRepository。

Answer 1

在使用基于java的配置时，我不认为它们相当于内部或本地bean。我可能会尝试在TimedRepositories bean方法中创建RealRepository，同时请求方法签名中的所有依赖项。但是，如果您真的需要使用spring来处理RealRepository依赖项，则需要使用bean工厂。

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(loader=AnnotationConfigContextLoader.class)
public class ConfigTest {

    @Autowired TimedRepository timedRepo;

    @Test
    public void testRepository() {
        Assert.assertNotNull(timedRepo);
    }


    @Configuration
    static class TimedRepositoryConfiguration {

        @Autowired
        private AutowireCapableBeanFactory beanFactory;

        @Bean
        public TimedRepository timedRepository() {
            RealRepository realRepository = (RealRepository) beanFactory.createBean(RealRepository.class, AutowireCapableBeanFactory.AUTOWIRE_CONSTRUCTOR, true);
            return new TimedRepository(realRepository);
        }

        public RealRepository realRepository() {
            return new RealRepository();
        }
    }

    static class RealRepository {

    }

    static class TimedRepository {

        private RealRepository realRepo;

        public TimedRepository(RealRepository r) {
            this.realRepo = r;
        }
    }

}

Answer 2

您可以手动实例化bean：

public class BeanThatDependsOnRealRepository() {

  private final Repository repository;

  @Inject
  public BeanThatDependsOnRealRepository(DataSource dataSource) {
    this.repository = new RealRepository(dataSource);
  }
}

这实质上是匿名内部bean在XML中的作用。您只是显式构造它并在封闭类的构造函数中从Spring获取其依赖项。

Answer 3

最新答案，但这在Spring Core 4+（可能还有Spring Core 3）中可能会有些诡异。

虽然标准Spring语义不支持使用JavaConfig创建内部bean，但是可以利用内部bean周围的内部功能来产生相同的结果。

BeanDefinitionValueResolver（请参阅BeanDefinitionValueResolver#resolveValueIfNecessary）在属性值解析期间生成了内部bean。在Spring中，“内部bean”的概念主要包含在该值解析器（它是内部bean的唯一生产者）之内，并且在术语“包含的bean”（来自父类DefaultSingletonBeanRegistry）的bean工厂中也包含在内。 >

根据BeanDefinition中提出的解析策略，我们可以通过将属性定义为BeanDefinitionValueResolver来诱使Spring产生其他内部bean：

@Configuration
public class MyConfiguration {

    private static Logger logger = LoggerFactory.getLogger(MyConfiguration.class);

    private RealRepository realRepository;
    private Timer timer;


    public MyConfiguration(@SuppressWarnings("SpringJavaInjectionPointsAutowiringInspection") RealRepository realRepository, Timer timer) {
        this.realRepository = realRepository;
        this.timer = timer;
        logger.info("Constructed MyConfiguration {}", this);
    }


    @Bean
    public TimedRepository timedRepository() {
        TimedRepository timedRepository = new TimedRepository(this.realRepository, this.timer);
        logger.info("Created timed repo: {}", timedRepository);
        return timedRepository;
    }


    public RealRepository realRepository(DataSource dataSource) {
        RealRepository realRepository = new RealRepository(dataSource);
        logger.info("Created real repo: {}", realRepository);
        return realRepository;
    }


    @Override
    public String toString() {
        return "MyConfiguration{" +
                "realRepository=" + realRepository +
                ", timer=" + timer +
                '}';
    }
}

@Component
public class InnerBeanInjectionBeanFactoryPostProcessor implements BeanDefinitionRegistryPostProcessor, PriorityOrdered {

    @Override
    public int getOrder() {
        // Preempt execution of org.springframework.context.annotation.ConfigurationClassPostProcessor
        return 0;
    }


    @Override
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
        String[] beanDefinitionNameList = ((ConfigurableListableBeanFactory) registry).getBeanNamesForType(MyConfiguration.class, true, false);
        assert beanDefinitionNameList.length == 1;
        BeanDefinition configurationBeanDefinition = registry.getBeanDefinition(beanDefinitionNameList[0]);
        BeanDefinition realRepositoryBeanDefinition = BeanDefinitionBuilder.genericBeanDefinition(MyConfiguration.class)
                .setScope(BeanDefinition.SCOPE_SINGLETON)
                .setFactoryMethod("realRepository")
                .setAutowireMode(RootBeanDefinition.AUTOWIRE_CONSTRUCTOR)
                .getBeanDefinition();
        configurationBeanDefinition.getConstructorArgumentValues()
                .addGenericArgumentValue(realRepositoryBeanDefinition);
    }


    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
        // Do nothing
    }
}

此解决方案的一个明显问题是，它需要通过BeanDefinitionRegistryPostProcessor进行手动处理，这在此不费吹灰之力。我建议的是以下内容：

创建自定义注释（例如@InnerBean）
将此注释附加到@Configuration类中的方法和所需的候选组件类中
使BeanDefinitionRegistryPostProcessor适应扫描带有@InnerBean注释的静态方法的类（应在#postProcessBeanFactory中扫描组件类，并在#postProcessBeanDefinitionRegistry中扫描配置类）
将Bean定义附加到包含Bean定义的自动装配的构造函数字段（如果是您的约定，则为setter字段）

以下是示例：

@Target(ElementType.METHOD)
public @interface InnerBean {
}

@Configuration
public class MyConfiguration {

    private static Logger logger = LoggerFactory.getLogger(MyConfiguration.class);

    private RealRepository realRepository;
    private Timer timer;


    public MyConfiguration(@SuppressWarnings("SpringJavaInjectionPointsAutowiringInspection") RealRepository realRepository, Timer timer) {
        this.realRepository = realRepository;
        this.timer = timer;
        logger.info("Constructed MyConfiguration {}", this);
    }


    @Bean
    public TimedRepository timedRepository() {
        TimedRepository timedRepository = new TimedRepository(this.realRepository, this.timer);
        logger.info("Created timed repo: {}", timedRepository);
        return timedRepository;
    }


    @InnerBean
    public static RealRepository realRepository(DataSource dataSource) {
        RealRepository realRepository = new RealRepository(dataSource);
        logger.info("Created real repo: {}", realRepository);
        return realRepository;
    }


    @Override
    public String toString() {
        return "MyConfiguration{" +
                "realRepository=" + realRepository +
                ", timer=" + timer +
                '}';
    }
}

@Component
public class InnerBeanInjectionBeanFactoryPostProcessor implements BeanDefinitionRegistryPostProcessor, PriorityOrdered {

    private static Logger logger = LoggerFactory.getLogger(InnerBeanInjectionBeanFactoryPostProcessor.class);

    private Set<BeanDefinition> processedBeanDefinitionSet = new HashSet<>();


    @Override
    public int getOrder() {
        // Preempt execution of org.springframework.context.annotation.ConfigurationClassPostProcessor
        return 0;
    }


    @Override
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
        ConfigurableListableBeanFactory beanFactory = (ConfigurableListableBeanFactory) registry;
        String[] configBeanDefinitionNames = beanFactory.getBeanNamesForAnnotation(Configuration.class);
        Arrays.stream(configBeanDefinitionNames)
                .map(beanFactory::getBeanDefinition)
                .filter(this::isCandidateBean)
                .peek(this.processedBeanDefinitionSet::add)
                .forEach(this::autowireInnerBeans);
    }


    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
        Arrays.stream(beanFactory.getBeanDefinitionNames())
                .map(beanFactory::getBeanDefinition)
                .filter(this::isCandidateBean)
                .filter(beanDefinition -> !this.processedBeanDefinitionSet.contains(beanDefinition))
                .forEach(this::autowireInnerBeans);
    }


    private boolean isCandidateBean(BeanDefinition beanDefinition) {
        return beanDefinition.getBeanClassName() != null && beanDefinition.getBeanClassName().startsWith("com.example.demo.");
    }


    private void autowireInnerBeans(BeanDefinition beanDefinition) {
        // Get @InnerBean methods
        assert beanDefinition instanceof AnnotatedBeanDefinition;
        AnnotatedBeanDefinition annotatedBeanDefinition = (AnnotatedBeanDefinition) beanDefinition;
        Set<MethodMetadata> innerBeanMethods = annotatedBeanDefinition.getMetadata().getAnnotatedMethods(InnerBean.class.getName());

        // Attach inner beans as constructor parameters
        for (MethodMetadata method : innerBeanMethods) {
            String innerBeanName = method.getMethodName();
            if (!method.isStatic()) {
                logger.error("@InnerBean definition [{}] is non-static. Inner beans must be defined using static factory methods.", innerBeanName);
                continue;
            }

            BeanDefinition innerBeanDefinition = BeanDefinitionBuilder.genericBeanDefinition(beanDefinition.getBeanClassName())
                    .setScope(BeanDefinition.SCOPE_SINGLETON)
                    .setAutowireMode(RootBeanDefinition.AUTOWIRE_CONSTRUCTOR)
                    .setFactoryMethod(innerBeanName)
                    .getBeanDefinition();
            beanDefinition.getConstructorArgumentValues()
                    .addGenericArgumentValue(new ConstructorArgumentValues.ValueHolder(innerBeanDefinition, method.getReturnTypeName(), method.getMethodName()));
        }
    }
}

这样做会带来一些好处和警告。一个很大的好处是，bean的生命周期将由Spring IoC容器管理，这意味着将调用生命周期回调（例如@PostConstruct和@PreDestroy）。可以根据父代的生命周期自动对其进行管理。需要注意的是，不能将bean作为工厂方法参数注入（尽管您可以做一些工作，但您可能可以解决此问题），并且AOP代理将不会应用于@Configuration类中的这些方法（即{{ 1}}永远不要被调用，因为它不会引用单例内部Bean；相反，应始终引用实例字段）。为了应用此功能，需要添加进一步的代理（类似于ConfigurationClassEnhancer.BeanMethodInterceptor）。

Spring 3.1 Java配置和内部bean

3 个答案: