XML配置下Spring Bean的注入

主题

之前学习了@Autowired下SpringBean是怎么注入到属性中的.

https://www.cnblogs.com/abcwt112/p/12541783.html

现在学习下远古时代的XML是怎么注入的.

Ac初始化

入口是XML的AC.

new的时候回做refresh方法

refresh之前的文章分享过大致做了什么

https://www.cnblogs.com/abcwt112/p/12388982.html

 其中这一步会去掉BeanFactory的getBean方法去初始化配置的bean.

属性注入

BF的getBean里面有无数逻辑.其中注入属性的是这一段

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#populateBean

/**
     * 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 the BeanWrapper with bean instance
     */
    @SuppressWarnings("deprecation")  // for postProcessPropertyValues
    protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
        if (bw == null) {
            if (mbd.hasPropertyValues()) {
                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;
        }

        PropertyValues pvs = (mbd.hasPropertyValues() ? mbd.getPropertyValues() : null);

        int resolvedAutowireMode = mbd.getResolvedAutowireMode();
        if (resolvedAutowireMode == AUTOWIRE_BY_NAME || resolvedAutowireMode == AUTOWIRE_BY_TYPE) {
            MutablePropertyValues newPvs = new MutablePropertyValues(pvs);
            // Add property values based on autowire by name if applicable.
            if (resolvedAutowireMode == AUTOWIRE_BY_NAME) {
                autowireByName(beanName, mbd, bw, newPvs);
            }
            // Add property values based on autowire by type if applicable.
            if (resolvedAutowireMode == AUTOWIRE_BY_TYPE) {
                autowireByType(beanName, mbd, bw, newPvs);
            }
            pvs = newPvs;
        }

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

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

        if (pvs != null) {
            applyPropertyValues(beanName, mbd, bw, pvs);
        }
    }

如果XML里bean是这样配置的:

 其中最后91行的 applyPropertyValues(beanName, mbd, bw, pvs);

就是把对象中的属性(pvs)转化成对象,设置到bw(BeanWrapper.封装了原始对象)中去.

比如beanName是a.     pvs是a对象里的属性集,其中包含b

具体逻辑是调用Object resolvedValue = valueResolver.resolveValueIfNecessary(pv, originalValue); 来获取要注入的属性对应的bean.

 最终也是通过BF.getBean去取Bean.再set到beanwrapper上去.

XML配置中还有一种情况是使用默认的自动配置

这个时候bean的属性是不需要配置的.spring会自动根据类型(byType)或者名称(byName)去匹配.

原理是在org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#populateBean中

        int resolvedAutowireMode = mbd.getResolvedAutowireMode();
        if (resolvedAutowireMode == AUTOWIRE_BY_NAME || resolvedAutowireMode == AUTOWIRE_BY_TYPE) {
            MutablePropertyValues newPvs = new MutablePropertyValues(pvs);
            // Add property values based on autowire by name if applicable.
            if (resolvedAutowireMode == AUTOWIRE_BY_NAME) {
                autowireByName(beanName, mbd, bw, newPvs);
            }
            // Add property values based on autowire by type if applicable.
            if (resolvedAutowireMode == AUTOWIRE_BY_TYPE) {
                autowireByType(beanName, mbd, bw, newPvs);
            }
            pvs = newPvs;
        }

resolvedAutowireMode默认情况下是0.是不会自动装配的.如果配置了就会进对应的autowiredByXXX方法.会找出missing property values然后设置到MutablePropertyValues中.所以最后掉applyPropertyValues方法的时候还是会填充这些属性.