<beans default-autowire="byType />

意味着如果具有所需类型的 bean 不超过 1 个，bean 的所有字段将自动注入(inject)依赖项。

问题是当使用注解时它是如何工作的，它到底能不能工作。

我的测试表明即使我使用

@Resource(name="someConcreteFoo")
private Foo foo;

如果 Foo 有多个实现，上下文会尝试按类型 Autowiring 字段，但会失败.所以，就我所见，default-autowire不与注释混合。我在文档中找不到任何具体内容。

扩展问题 - 当使用 xml-only 时，spring 如何使用默认 Autowiring 。 IE。如果你有 <property> .属性注入(inject)是否覆盖默认值(应该是)。

我可以做更多的测试，但我更喜欢通过一些引用来确认行为。有什么见解吗？

最佳答案

我快速调试了这个问题，我认为这很可能是 spring 中的一个错误。在我看来，问题源于AbstractAutowireCapableBeanFactory中的以下代码

/**
 * Populate the bean instance in the given BeanWrapper with the property values
 * from the bean definition.
 * @param beanName the name of the bean
 * @param mbd the bean definition for the bean
 * @param bw BeanWrapper with bean instance
 */
protected void populateBean(String beanName, AbstractBeanDefinition mbd, BeanWrapper bw) {
    PropertyValues pvs = mbd.getPropertyValues();

    if (bw == null) {
        if (!pvs.isEmpty()) {
            throw new BeanCreationException(
                    mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance");
        }
        else {
            // Skip property population phase for null instance.
            return;
        }
    }

    // Give any InstantiationAwareBeanPostProcessors the opportunity to modify the
    // state of the bean before properties are set. This can be used, for example,
    // to support styles of field injection.
    boolean continueWithPropertyPopulation = true;

    if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
        for (BeanPostProcessor bp : getBeanPostProcessors()) {
            if (bp instanceof InstantiationAwareBeanPostProcessor) {
                InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
                if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
                    continueWithPropertyPopulation = false;
                    break;
                }
            }
        }
    }

    if (!continueWithPropertyPopulation) {
        return;
    }

    if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME ||
            mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
        MutablePropertyValues newPvs = new MutablePropertyValues(pvs);

        // Add property values based on autowire by name if applicable.
        if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) {
            autowireByName(beanName, mbd, bw, newPvs);
        }

        // Add property values based on autowire by type if applicable.
        if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
            autowireByType(beanName, mbd, bw, newPvs);
        }

        pvs = newPvs;
    }

    boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
    boolean needsDepCheck = (mbd.getDependencyCheck() != RootBeanDefinition.DEPENDENCY_CHECK_NONE);

    if (hasInstAwareBpps || needsDepCheck) {
        PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw);
        if (hasInstAwareBpps) {
            for (BeanPostProcessor bp : getBeanPostProcessors()) {
                if (bp instanceof InstantiationAwareBeanPostProcessor) {
                    InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
                    pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
                    if (pvs == null) {
                        return;
                    }
                }
            }
        }
        if (needsDepCheck) {
            checkDependencies(beanName, mbd, filteredPds, pvs);
        }
    }

    applyPropertyValues(beanName, mbd, bw, pvs);
}

我个人认为应用 Autowiring 和 InstantiationAwareBeanPostProcessor 的顺序是错误的，因为 @Resource 注释只会在 postProcessPropertyValues 中应用，所以在 Autowiring 之后(此时 Autowiring 已经失败)。

现在我不知道更改调用顺序是否会产生影响，以便在 Autowiring 之前解决 @Resource 注释，但这很可能是一个错误/修复(我使用按照加载我的测试应用程序上下文的方式来解决此问题):

    ApplicationContext ctx = new ClassPathXmlApplicationContext("test/appctx.xml") {
        protected org.springframework.beans.factory.support.DefaultListableBeanFactory createBeanFactory() {
            return new DefaultListableBeanFactory(getInternalParentBeanFactory()) {
                protected void populateBean(String beanName, org.springframework.beans.factory.support.AbstractBeanDefinition mbd, org.springframework.beans.BeanWrapper bw) {
                    PropertyValues pvs = mbd.getPropertyValues();

                    if (bw == null) {
                        if (!pvs.isEmpty()) {
                            throw new BeanCreationException(
                                    mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance");
                        }
                        else {
                            // Skip property population phase for null instance.
                            return;
                        }
                    }

                    // Give any InstantiationAwareBeanPostProcessors the opportunity to modify the
                    // state of the bean before properties are set. This can be used, for example,
                    // to support styles of field injection.
                    boolean continueWithPropertyPopulation = true;

                    if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
                        for (BeanPostProcessor bp : getBeanPostProcessors()) {
                            if (bp instanceof InstantiationAwareBeanPostProcessor) {
                                InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
                                if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
                                    continueWithPropertyPopulation = false;
                                    break;
                                }
                            }
                        }
                    }

                    if (!continueWithPropertyPopulation) {
                        return;
                    }

                    boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
                    boolean needsDepCheck = (mbd.getDependencyCheck() != RootBeanDefinition.DEPENDENCY_CHECK_NONE);

                    if (hasInstAwareBpps || needsDepCheck) {
                        PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw);
                        if (hasInstAwareBpps) {
                            for (BeanPostProcessor bp : getBeanPostProcessors()) {
                                if (bp instanceof InstantiationAwareBeanPostProcessor) {
                                    InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
                                    pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
                                    if (pvs == null) {
                                        return;
                                    }
                                }
                            }
                        }
                        if (needsDepCheck) {
                            checkDependencies(beanName, mbd, filteredPds, pvs);
                        }
                    }

                    if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME ||
                            mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
                        MutablePropertyValues newPvs = new MutablePropertyValues(pvs);

                        // Add property values based on autowire by name if applicable.
                        if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) {
                            autowireByName(beanName, mbd, bw, newPvs);
                        }

                        // Add property values based on autowire by type if applicable.
                        if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
                            autowireByType(beanName, mbd, bw, newPvs);
                        }

                        pvs = newPvs;
                    }

                    applyPropertyValues(beanName, mbd, bw, pvs);
                }
            };
        }
    };

希望对你有帮助

关于java - @Autowired 和 default-autowire 可以共存吗？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/5145351/