前言

喜欢我的文章的话就给个好评吧，你的肯定是我坚持写作最大的动力，来吧兄弟们，给我一点动力

这一章节我们来讨论创建Bean过程中的属性注入，在Spring的IOC容器启动过程中，会把定义的Bean封装成BeanDefinition注册到一个ConcurrentHashMap中，Bean注册完成后，就会对单利的且lazy-init=false 的Bean进行实例化。创建Bean的代码在 AbstractAutowireCapableBeanFactory#doCreateBean 中，当Bean创建成功之后，会调用AbstractAutowireCapableBeanFactory#populateBean 方法进行属性注入。本篇文章主要就是分析该方法是如何实现Bean的属性注入的。

这里先上一个属性注入的流程图，待会儿可以根据这个图来看代码

属性注入：AbstractAutowireCapableBeanFactory#populateBean

AbstractAutowireCapableBeanFactory#populateBean 方法的主要功能就是属性填充，源码如下

//使用 bean 定义中的属性值填充给定 BeanWrapper 中的 bean 实例。
    @SuppressWarnings("deprecation")  // for postProcessPropertyValues
    protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
   
   
        if (bw == null) {
   
   
            //判断是否有property属性
            if (mbd.hasPropertyValues()) {
   
   
                throw new BeanCreationException(
                        mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance");
            }
            else {
   
   
                //没有任何属性可以填充
                // 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.
        //让 InstantiationAwareBeanPostProcessors 也在属性注入之前改变Bean的状态
        if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
   
   
            for (BeanPostProcessor bp : getBeanPostProcessors()) {
   
   
                if (bp instanceof InstantiationAwareBeanPostProcessor) {
   
   
                    InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
                    if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
   
   
                        return;
                    }
                }
            }
        }
        //从 RootBeanDefinition 获取所有的PropertyValues
        PropertyValues pvs = (mbd.hasPropertyValues() ? mbd.getPropertyValues() : null);

        int resolvedAutowireMode = mbd.getResolvedAutowireMode();
        //根据名字获取根据type注入
        if (resolvedAutowireMode == AUTOWIRE_BY_NAME || resolvedAutowireMode == AUTOWIRE_BY_TYPE) {
   
   
            MutablePropertyValues newPvs = new MutablePropertyValues(pvs);
            // Add property values based on autowire by name if applicable.
            //如果适用，根据名称添加基于自动装配的属性值。
            if (resolvedAutowireMode == AUTOWIRE_BY_NAME) {
   
   
                autowireByName(beanName, mbd, bw, newPvs);
            }
            // Add property values based on autowire by type if applicable.
            //如果适用，根据类型添加基于自动装配的属性值
            if (resolvedAutowireMode == AUTOWIRE_BY_TYPE) {
   
   
                autowireByType(beanName, mbd, bw, newPvs);
            }
            pvs = newPvs;
        }
        //后置处理器是否已经注册,初始化好了
        boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
        //是否要检查依赖，默认false
        boolean needsDepCheck = (mbd.getDependencyCheck() != AbstractBeanDefinition.DEPENDENCY_CHECK_NONE);

        PropertyDescriptor[] filteredPds = null;
        if (hasInstAwareBpps) {
   
   
            if (pvs == null) {
   
   
                pvs = mbd.getPropertyValues();
            }
            //获取后置处理器
            for (BeanPostProcessor bp : getBeanPostProcessors()) {
   
   
                //如果是Bean实例化后置处理器
                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);
                        }
                        //对需要依赖检查的属性进行后置处理
                        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) {
   
   
            //依赖注入入口，讲属性应用到Bean中
            applyPropertyValues(beanName, mbd, bw, pvs);
        }
    }

方法中的重要代码

• autowireByName : 根据属性名进行注入
• autowireByType：根据类型注入Bean
• InstantiationAwareBeanPostProcessor.postProcessPropertyValues :该方法是在工厂将给定的属性值应用于给定的 bean 之前对给定的属性值进行处理，比如：RequiredAnnotationBeanPostProcessor类中对属性的验证。
• applyPropertyValues：属性的填充

AbstractAutowireCapableBeanFactory#autowireByName

autowireByName是根据名字注入，源码如下

protected void autowireByName(
            String beanName, AbstractBeanDefinition mbd, BeanWrapper bw, MutablePropertyValues pvs) {
   
   
        //寻找BeanWrapper中需要依赖的属性
        String[] propertyNames = unsatisfiedNonSimpleProperties(mbd, bw);
        for (String propertyName : propertyNames) {
   
   
            if (containsBean(propertyName)) {
   
   
                //递归实例化的Bean
                Object bean = getBean(propertyName);
                pvs.add(propertyName, bean);
                //注册依赖的Bean，加入 dependentBeanMap 中
                registerDependentBean(propertyName, beanName);
                if (logger.isTraceEnabled()) {
   
   
                    logger.trace("Added autowiring by name from bean name '" + beanName +
                            "' via property '" + propertyName + "' to bean named '" + propertyName + "'");
                }
            }
            else {
   
   
                if (logger.isTraceEnabled()) {
   
   
                    logger.trace("Not autowiring property '" + propertyName + "' of bean '" + beanName +
                            "' by name: no matching bean found");
                }
            }
        }
    }

这个方法很简单，就是先找到依赖的Bean，递归初始化，然后加入 pvs中

//定义“按类型自动装配”（按类型的 bean 属性）行为的抽象方法
    protected void autowireByType(
            String beanName, AbstractBeanDefinition mbd, BeanWrapper bw, MutablePropertyValues pvs) {
   
   
        //类型转换器
        TypeConverter converter = getCustomTypeConverter();
        if (converter == null) {
   
   
            converter = bw;
        }

        Set<String> autowiredBeanNames = new LinkedHashSet<>(4);
        //找到需要注入的属性
        String[] propertyNames = unsatisfiedNonSimpleProperties(mbd, bw);
        for (String propertyName : propertyNames) {
   
   
            try {
   
   
                //属性描述
                PropertyDescriptor pd = bw.getPropertyDescriptor(propertyName);
                // Don't try autowiring by type for type Object: never makes sense,
                // even if it technically is a unsatisfied, non-simple property.
                if (Object.class != pd.getPropertyType()) {
   
   
                    //获取对象的set方法
                    MethodParameter methodParam = BeanUtils.getWriteMethodParameter(pd);
                    // Do not allow eager init for type matching in case of a prioritized post-processor.

                    boolean eager = !(bw.getWrappedInstance() instanceof PriorityOrdered);
                    //依赖描述
                    DependencyDescriptor desc = new AutowireByTypeDependencyDescriptor(methodParam, eager);
                    //【重要】得到依赖的属性的值，存储到 autowiredBeanNames 集合中
                    //提供了对集合如：@Autowired private List<A> as; 支持，根据类型走到所有的Bean注入其中
                    Object autowiredArgument = resolveDependency(desc, beanName, autowiredBeanNames, converter);
                    if (autowiredArgument != null) {
   
   
                        //添加到pvs
                        pvs.add(propertyName, autowiredArgument);
                    }
                    for (String autowiredBeanName : autowiredBeanNames) {
   
   
                        //注入依赖的Bean
                        registerDependentBean(autowiredBeanName, beanName);
                        if (logger.isTraceEnabled()) {
   
   
                            logger.trace("Autowiring by type from bean name '" + beanName + "' via property '" +
                                    propertyName + "' to bean named '" + autowiredBeanName + "'");
                        }
                    }
                    //清理掉依赖
                    autowiredBeanNames.clear();
                }
            }
            catch (BeansException ex) {
   
   
                throw new UnsatisfiedDependencyException(mbd.getResourceDescription(), beanName, propertyName, ex);
            }
        }
    }

看到这，我们大概清楚了，其实在populateBean 方法中会先从RootBeanDefinition 中获取 Bean的属性(PropertyValues)，同时也会根据RootBeanDefinition的autowireMode自动注入模式来根据name或者type寻主Bean的依赖的属性。

根据类型注入和根据名字注入都是先从BeanWrapper 中找到Bean的依赖的属性，然后根据属性类型找到匹配的Bean，实现依赖注入。还提供了对集合如：@Autowired private List<A> as; 集合注入的支持。

属性寻找好之后都会封装成 PropertyValues，然后传给applyPropertyValues应用到Bean身上。

AbstractAutowireCapableBeanFactory#applyPropertyValues

我们可以认为前面的代码是在为当前Bean寻找依赖的的属性，封装到 PropertyValues中，在applyPropertyValues中才是把属性应用到当前Bean。

//处理对象之间的引用，使用深拷贝
    protected void applyPropertyValues(String beanName, BeanDefinition mbd, BeanWrapper bw, PropertyValues pvs) {
   
   
        if (pvs.isEmpty()) {
   
   
            return;
        }

        if (System.getSecurityManager() != null && bw instanceof BeanWrapperImpl) {
   
   
            ((BeanWrapperImpl) bw).setSecurityContext(getAccessControlContext());
        }

        MutablePropertyValues mpvs = null;
        List<PropertyValue> original;

        if (pvs instanceof MutablePropertyValues) {
   
   
            mpvs = (MutablePropertyValues) pvs;
            //判断mpvs中的值是否已经转成了对应的类型，已经转了就可以直接设置值到 BeanWrapper了
            if (mpvs.isConverted()) {
   
   
                // Shortcut: use the pre-converted values as-is.
                try {
   
   
                    //为实例化对象设置属性
                    bw.setPropertyValues(mpvs);
                    return;
                }
                catch (BeansException ex) {
   
   
                    throw new BeanCreationException(
                            mbd.getResourceDescription(), beanName, "Error setting property values", ex);
                }
            }
            //获取属性值的原始类型
            original = mpvs.getPropertyValueList();
        }
        else {
   
   
            //如果类型不是MutablePropertyValues ， 就使用原生属性获取方法
            original = Arrays.asList(pvs.getPropertyValues());
        }
        //获取用户自定义的型转换器
        TypeConverter converter = getCustomTypeConverter();
        if (converter == null) {
   
   
            converter = bw;
        }
        //解析器：用于 bean 工厂实现的 Helper 类，将 bean 定义对象中包含的值，解析为应用于目标 bean 实例的实际值。
        BeanDefinitionValueResolver valueResolver = new BeanDefinitionValueResolver(this, beanName, mbd, converter);

        // Create a deep copy, resolving any references for values.
        //存放类型转换过的属性，把Bean的属性解析值新建拷贝，把拷贝的数据注入到对象
        List<PropertyValue> deepCopy = new ArrayList<>(original.size());
        boolean resolveNecessary = false;
        //类型转换，把属性转换为对应的类型
        for (PropertyValue pv : original) {
   
   
            if (pv.isConverted()) {
   
   
            //属性值不需要转
                deepCopy.add(pv);
            }
            else {
   
   
                //属性名
                String propertyName = pv.getName();
                //原始属性值，它的类型是一个 如： RuntimeBeanReference<otherBean> 引用类型
                Object originalValue = pv.getValue();
                //转换属性值，将引用转换为 IOC 容器中实例化对象引用  OtherBean
                Object resolvedValue = valueResolver.resolveValueIfNecessary(pv, originalValue);
                Object convertedValue = resolvedValue;

                boolean convertible = bw.isWritableProperty(propertyName) &&
                        !PropertyAccessorUtils.isNestedOrIndexedProperty(propertyName);
                if (convertible) {
   
   
                    //使用用户自定义的转换器转换
                    convertedValue = convertForProperty(resolvedValue, propertyName, bw, converter);
                }
                // Possibly store converted value in merged bean definition,
                // in order to avoid re-conversion for every created bean instance.
                if (resolvedValue == originalValue) {
   
   
                    if (convertible) {
   
   
                        //设置转换之后的值到PV ，把依赖的Bean设置给PropertyValue
                        pv.setConvertedValue(convertedValue);
                    }
                    deepCopy.add(pv);
                }
                else if (convertible && originalValue instanceof TypedStringValue &&
                        !((TypedStringValue) originalValue).isDynamic() &&
                        !(convertedValue instanceof Collection || ObjectUtils.isArray(convertedValue))) {
   
   
                    pv.setConvertedValue(convertedValue);
                    deepCopy.add(pv);
                }
                else {
   
   
                    resolveNecessary = true;
                    //转换好的依赖的属性最终放到一个ArrayList中
                    deepCopy.add(new PropertyValue(pv, convertedValue));
                }
            }
        }
        if (mpvs != null && !resolveNecessary) {
   
   
            mpvs.setConverted();
        }

        // Set our (possibly massaged) deep copy.
        try {
   
   
            //把解析好的属性 设置到 BeanWrapper 中
            bw.setPropertyValues(new MutablePropertyValues(deepCopy));
        }
        catch (BeansException ex) {
   
   
            throw new BeanCreationException(
                    mbd.getResourceDescription(), beanName, "Error setting property values", ex);
        }
    }

这里主要进行属性转换，然后应用到Bean身上，这里的属性转换比如: 在BeanDefinition中属性可能是用字符串类型来描述的，需要把属性转成真实的原始属性类型。

• 首先判断属性是否需要转换类型，如果不需要转直接应用于Bean。比如：<property name="otherBean" ref="otherBean" /> 这种属性值其实是个字符串“otherBean” ，需要解析成容器中的OtherBean实例的引用。
• 如果属性值需要类型转换，比如：属性值是容器中的另外一个Bean，则需要根据属性值解析出引用的对象然后注入到对象的属性上，应用到Bean。

通过 BeanDefinitionValueResolver 类中的 resolveValueIfNecessary()方法中进行属性值的解析， 对属性值的注入是通过 bw.setPropertyValues()方法完成

解析： BeanDefinitionValueResolver#resolveValueIfNecessary

给定一个 PropertyValue根据属性值进行类型解析，必要时解析对工厂中其他 bean 的引用

@Nullable
    public Object resolveValueIfNecessary(Object argName, @Nullable Object value) {
   
   
        // We must check each value to see whether it requires a runtime reference
        // to another bean to be resolved.
        //对属性值是引用类型的解析
        if (value instanceof RuntimeBeanReference) {
   
   
            //比如：<property name="xx" ref="xxBean" 就是引用类型，会走这里
            RuntimeBeanReference ref = (RuntimeBeanReference) value;
            //对引用类型属性进行解析
            return resolveReference(argName, ref);
        }
        ///对属性值是引用容器中另一个 Bean 名称的解析
        else if (value instanceof RuntimeBeanNameReference) {
   
   
            String refName = ((RuntimeBeanNameReference) value).getBeanName();
            refName = String.valueOf(doEvaluate(refName));
            //判断容器中是否有这个Bean
            if (!this.beanFactory.containsBean(refName)) {
   
   
                throw new BeanDefinitionStoreException(
                        "Invalid bean name '" + refName + "' in bean reference for " + argName);
            }
            return refName;
        }
        else if (value instanceof BeanDefinitionHolder) {
   
   
            // Resolve BeanDefinitionHolder: contains BeanDefinition with name and aliases.
            //解析 BeanDefinitionHolder：包含带有名称和别名的 BeanDefinition
            BeanDefinitionHolder bdHolder = (BeanDefinitionHolder) value;
            //解析内部 Bean
            return resolveInnerBean(argName, bdHolder.getBeanName(), bdHolder.getBeanDefinition());
        }
        else if (value instanceof BeanDefinition) {
   
   
            // Resolve plain BeanDefinition, without contained name: use dummy name.
            //解析纯 BeanDefinition，不包含名称
            BeanDefinition bd = (BeanDefinition) value;
            String innerBeanName = "(inner bean)" + BeanFactoryUtils.GENERATED_BEAN_NAME_SEPARATOR +
                    ObjectUtils.getIdentityHexString(bd);
            return resolveInnerBean(argName, innerBeanName, bd);
        }
        //对数组类型解析
        else if (value instanceof ManagedArray) {
   
   
            // May need to resolve contained runtime references.
            ManagedArray array = (ManagedArray) value;
            Class<?> elementType = array.resolvedElementType;
            if (elementType == null) {
   
   
                String elementTypeName = array.getElementTypeName();
                if (StringUtils.hasText(elementTypeName)) {
   
   
                    try {
   
   
                        elementType = ClassUtils.forName(elementTypeName, this.beanFactory.getBeanClassLoader());
                        array.resolvedElementType = elementType;
                    }
                    catch (Throwable ex) {
   
   
                        // Improve the message by showing the context.
                        throw new BeanCreationException(
                                this.beanDefinition.getResourceDescription(), this.beanName,
                                "Error resolving array type for " + argName, ex);
                    }
                }
                else {
   
   
                    elementType = Object.class;
                }
            }
            return resolveManagedArray(argName, (List<?>) value, elementType);
        }
        //对集合类型解析
        else if (value instanceof ManagedList) {
   
   
            // May need to resolve contained runtime references.
            return resolveManagedList(argName, (List<?>) value);
        }
        //对Set类型解析
        else if (value instanceof ManagedSet) {
   
   
            // May need to resolve contained runtime references.
            return resolveManagedSet(argName, (Set<?>) value);
        }
        //对Map类型解析
        else if (value instanceof ManagedMap) {
   
   
            // May need to resolve contained runtime references.
            return resolveManagedMap(argName, (Map<?, ?>) value);
        }
        //对Properties解析
        else if (value instanceof ManagedProperties) {
   
   
            Properties original = (Properties) value;
            Properties copy = new Properties();
            original.forEach((propKey, propValue) -> {
   
   
                if (propKey instanceof TypedStringValue) {
   
   
                    propKey = evaluate((TypedStringValue) propKey);
                }
                if (propValue instanceof TypedStringValue) {
   
   
                    propValue = evaluate((TypedStringValue) propValue);
                }
                if (propKey == null || propValue == null) {
   
   
                    throw new BeanCreationException(
                            this.beanDefinition.getResourceDescription(), this.beanName,
                            "Error converting Properties key/value pair for " + argName + ": resolved to null");
                }
                copy.put(propKey, propValue);
            });
            return copy;
        }
        //解析字符串类型的属性值
        else if (value instanceof TypedStringValue) {
   
   
            // Convert value to target type here.
            TypedStringValue typedStringValue = (TypedStringValue) value;
            Object valueObject = evaluate(typedStringValue);
            try {
   
   
                //目标类型
                Class<?> resolvedTargetType = resolveTargetType(typedStringValue);
                if (resolvedTargetType != null) {
   
   
                    //目标类型进行解析
                    return this.typeConverter.convertIfNecessary(valueObject, resolvedTargetType);
                }
                else {
   
   
                    //类型没获取到，就返回Object类型
                    return valueObject;
                }
            }
            catch (Throwable ex) {
   
   
                // Improve the message by showing the context.
                throw new BeanCreationException(
                        this.beanDefinition.getResourceDescription(), this.beanName,
                        "Error converting typed String value for " + argName, ex);
            }
        }
        else if (value instanceof NullBean) {
   
   
            return null;
        }
        else {
   
   
            return evaluate(value);
        }
    }

这个方法中就是根据属性的值的类型进行解析，如：String，Array,List,Set,Map的类型，比较复杂的就是属性值依赖的是一个Bean，那么就需要根据依赖的Bean的名字找到容器中的Bean的实例，查找如下：

/**
     * Resolve a reference to another bean in the factory.
     */
     //关联对象的解析
    @Nullable
    private Object resolveReference(Object argName, RuntimeBeanReference ref) {
   
   
        try {
   
   
            Object bean;
            //引用对象的名称
            String refName = ref.getBeanName();
            refName = String.valueOf(doEvaluate(refName));
            //如果对象在父容器中，从父容器获取
            if (ref.isToParent()) {
   
   
                if (this.beanFactory.getParentBeanFactory() == null) {
   
   
                    throw new BeanCreationException(
                            this.beanDefinition.getResourceDescription(), this.beanName,
                            "Can't resolve reference to bean '" + refName +
                                    "' in parent factory: no parent factory available");
                }
                //如果对象在父容器中，从父容器获取
                bean = this.beanFactory.getParentBeanFactory().getBean(refName);
            }
            else {
   
   
                //[重要]根据依赖的Bean的名字，从当前容器中获取Bean
                bean = this.beanFactory.getBean(refName);
                //把依赖的Bean的实例和当前对象建议依赖关系，使用 dependentBeanMap 去维护关系
                this.beanFactory.registerDependentBean(refName, this.beanName);
            }
            if (bean instanceof NullBean) {
   
   
                bean = null;
            }
            return bean;
        }
        catch (BeansException ex) {
   
   
            throw new BeanCreationException(
                    this.beanDefinition.getResourceDescription(), this.beanName,
                    "Cannot resolve reference to bean '" + ref.getBeanName() + "' while setting " + argName, ex);
        }
    }



 * For each element in the managed array, resolve reference if necessary.
     */
     //解析数组
    private Object resolveManagedArray(Object argName, List<?> ml, Class<?> elementType) {
   
   
        Object resolved = Array.newInstance(elementType, ml.size());
        for (int i = 0; i < ml.size(); i++) {
   
   
            Array.set(resolved, i, resolveValueIfNecessary(new KeyedArgName(argName, i), ml.get(i)));
        }
        return resolved;
    }

    /**
     * For each element in the managed list, resolve reference if necessary.
     */
     //解析List
    private List<?> resolveManagedList(Object argName, List<?> ml) {
   
   
        List<Object> resolved = new ArrayList<>(ml.size());
        for (int i = 0; i < ml.size(); i++) {
   
   
            resolved.add(resolveValueIfNecessary(new KeyedArgName(argName, i), ml.get(i)));
        }
        return resolved;
    }

    /**
     * For each element in the managed set, resolve reference if necessary.
     */
     //解析set
    private Set<?> resolveManagedSet(Object argName, Set<?> ms) {
   
   
        Set<Object> resolved = new LinkedHashSet<>(ms.size());
        int i = 0;
        for (Object m : ms) {
   
   
            resolved.add(resolveValueIfNecessary(new KeyedArgName(argName, i), m));
            i++;
        }
        return resolved;
    }

    /**
     * For each element in the managed map, resolve reference if necessary.
     */
     //解析Map
    private Map<?, ?> resolveManagedMap(Object argName, Map<?, ?> mm) {
   
   
        Map<Object, Object> resolved = new LinkedHashMap<>(mm.size());
        mm.forEach((key, value) -> {
   
   
            Object resolvedKey = resolveValueIfNecessary(argName, key);
            Object resolvedValue = resolveValueIfNecessary(new KeyedArgName(argName, key), value);
            resolved.put(resolvedKey, resolvedValue);
        });
        return resolved;
    }

属性值解析完成之后 是封装成一个 MutablePropertyValues，通过 BeanWrapperImpl.setPropertyValues()方法完成值的注入，BeanWrapperImpl中注入方法又是由AbstractPropertyAccessor#setPropertyValue(java.lang.String, java.lang.Object)去完成。

AbstractPropertyAccessor#setPropertyValue

@Override
    public void setPropertyValues(PropertyValues pvs, boolean ignoreUnknown, boolean ignoreInvalid)
            throws BeansException {
   
   

        List<PropertyAccessException> propertyAccessExceptions = null;
        //拿到所有的属性列表
        List<PropertyValue> propertyValues = (pvs instanceof MutablePropertyValues ?
                ((MutablePropertyValues) pvs).getPropertyValueList() : Arrays.asList(pvs.getPropertyValues()));
        for (PropertyValue pv : propertyValues) {
   
   
            try {
   
   
                // This method may throw any BeansException, which won't be caught
                // here, if there is a critical failure such as no matching field.
                // We can attempt to deal only with less serious exceptions.
                //设置属性值
                setPropertyValue(pv);
            }
            ...省略...

@Override
    public void setPropertyValue(String propertyName, @Nullable Object value) throws BeansException {
   
   
        //属性访问器
        AbstractNestablePropertyAccessor nestedPa;
        try {
   
   
            nestedPa = getPropertyAccessorForPropertyPath(propertyName);
        }
        catch (NotReadablePropertyException ex) {
   
   
            throw new NotWritablePropertyException(getRootClass(), this.nestedPath + propertyName,
                    "Nested property in path '" + propertyName + "' does not exist", ex);
        }
        //属性助手
        PropertyTokenHolder tokens = getPropertyNameTokens(getFinalPath(nestedPa, propertyName));
        //通过属性访问器为属性设置值
        nestedPa.setPropertyValue(tokens, new PropertyValue(propertyName, value));
    }

这里看到，属性的注入交给了 AbstractNestablePropertyAccessor 属性访问器去完成

protected void setPropertyValue(PropertyTokenHolder tokens, PropertyValue pv) throws BeansException {
   
   
        if (tokens.keys != null) {
   
   
            processKeyedProperty(tokens, pv);
        }
        else {
   
   
            //走这里
            processLocalProperty(tokens, pv);
        }
    }

private void processLocalProperty(PropertyTokenHolder tokens, PropertyValue pv) {
   
   
        //属性处理器
        PropertyHandler ph = getLocalPropertyHandler(tokens.actualName);
        if (ph == null || !ph.isWritable()) {
   
   
            if (pv.isOptional()) {
   
   
                if (logger.isDebugEnabled()) {
   
   
                    logger.debug("Ignoring optional value for property '" + tokens.actualName +
                            "' - property not found on bean class [" + getRootClass().getName() + "]");
                }
                return;
            }
            else {
   
   
                throw createNotWritablePropertyException(tokens.canonicalName);
            }
        }

        Object oldValue = null;
        try {
   
   
            //原生值
            Object originalValue = pv.getValue();
            Object valueToApply = originalValue;
            ...省略...
            //这是重点，通过 PropertyHandler 把属性值设置给对象
            ph.setValue(valueToApply);
        }
        catch (TypeMismatchException ex) {
   
   
            throw ex;
        }

这里的属性值通过 PropertyHandler去设置

@Override
    public void setValue(@Nullable Object value) throws Exception {
   
   
        //得到属性的set方法
        Method writeMethod = (this.pd instanceof GenericTypeAwarePropertyDescriptor ?
                ((GenericTypeAwarePropertyDescriptor) this.pd).getWriteMethodForActualAccess() :
                this.pd.getWriteMethod());
        if (System.getSecurityManager() != null) {
   
   
            AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
   
   
                ReflectionUtils.makeAccessible(writeMethod);
                return null;
            });
            try {
   
   
                AccessController.doPrivileged((PrivilegedExceptionAction<Object>)
                        () -> writeMethod.invoke(getWrappedInstance(), value), acc);
            }
            catch (PrivilegedActionException ex) {
   
   
                throw ex.getException();
            }
        }
        else {
   
   
            //设置访问权限
            ReflectionUtils.makeAccessible(writeMethod);
            //调用set方法把属性值设置进去
            writeMethod.invoke(getWrappedInstance(), value);
        }
    }

这里就是得到属性的set方法，然后调用set方法把值注入进去。

构造器注入参数

在之前分析Bean的创建的时候我们就说到，在 AbstractAutowireCapableBeanFactory#createBeanInstance 中会通过反射获取到Bean的构造器，如果是有参构造就会走autowireConstructor 方法，通过有参构造创建实例

protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
   
   
        // Make sure bean class is actually resolved at this point.
        Class<?> beanClass = resolveBeanClass(mbd, beanName);

        ...省略...
        // Need to determine the constructor...
        Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
        if (ctors != null ||
                mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_CONSTRUCTOR ||
                mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args))  {
   
   
                //【重要】构造器注入参数
            return autowireConstructor(beanName, mbd, ctors, args);
        }

        // No special handling: simply use no-arg constructor.
        return instantiateBean(beanName, mbd);
    }

在autowireConstructor方法中会通过 ConstructorResolver 对构造器参数进行解析

protected BeanWrapper autowireConstructor(
            String beanName, RootBeanDefinition mbd, @Nullable Constructor<?>[] ctors, @Nullable Object[] explicitArgs) {
   
   
        //构造器解析器，注入
        return new ConstructorResolver(this).autowireConstructor(beanName, mbd, ctors, explicitArgs);
    }


public BeanWrapper autowireConstructor(final String beanName, final RootBeanDefinition mbd,
            @Nullable Constructor<?>[] chosenCtors, @Nullable final Object[] explicitArgs) {
   
   

        ...省略...
            else {
   
   
                //得到构造器参数
                ConstructorArgumentValues cargs = mbd.getConstructorArgumentValues();
                //得到构造器参数值
                resolvedValues = new ConstructorArgumentValues();
                //解析参数值【重要】
                minNrOfArgs = resolveConstructorArguments(beanName, mbd, bw, cargs, resolvedValues);
            }
        ...省略...
try {
   
   
            //实例化策略
            final InstantiationStrategy strategy = beanFactory.getInstantiationStrategy();
            Object beanInstance;

            if (System.getSecurityManager() != null) {
   
   
                final Constructor<?> ctorToUse = constructorToUse;
                final Object[] argumentsToUse = argsToUse;
                beanInstance = AccessController.doPrivileged((PrivilegedAction<Object>) () ->
                        strategy.instantiate(mbd, beanName, beanFactory, ctorToUse, argumentsToUse),
                        beanFactory.getAccessControlContext());
            }
            else {
   
   
                //实例化对象，根据有参构造器，使用反射创建实例
                beanInstance = strategy.instantiate(mbd, beanName, this.beanFactory, constructorToUse, argsToUse);
            }

            bw.setBeanInstance(beanInstance);
            return bw;
        }

resolveConstructorArguments 方法中又通过 BeanDefinitionValueResolver来解析属性值，有参数的值了，就会走反射，根据有参构造器创建实例返回。

private int resolveConstructorArguments(String beanName, RootBeanDefinition mbd, BeanWrapper bw,
            ConstructorArgumentValues cargs, ConstructorArgumentValues resolvedValues) {
   
   

        TypeConverter customConverter = this.beanFactory.getCustomTypeConverter();
        TypeConverter converter = (customConverter != null ? customConverter : bw);
        //属性值的解析器
        BeanDefinitionValueResolver valueResolver =
                new BeanDefinitionValueResolver(this.beanFactory, beanName, mbd, converter);

        ...省略...
        for (ConstructorArgumentValues.ValueHolder valueHolder : cargs.getGenericArgumentValues()) {
   
   
            if (valueHolder.isConverted()) {
   
   
                resolvedValues.addGenericArgumentValue(valueHolder);
            }
            else {
   
   
            //为构造器参数值做解析，这里和之前分析的set注入的属性值解析就一样了
                Object resolvedValue =
                        valueResolver.resolveValueIfNecessary("constructor argument", valueHolder.getValue());
                ConstructorArgumentValues.ValueHolder resolvedValueHolder = new ConstructorArgumentValues.ValueHolder(
                        resolvedValue, valueHolder.getType(), valueHolder.getName());
                resolvedValueHolder.setSource(valueHolder);
                resolvedValues.addGenericArgumentValue(resolvedValueHolder);
            }
        }

        return minNrOfArgs;
    }

因为之前 resolveValueIfNecessary方法已经分析过了，这里就不多说了。

总结

到这里属性注入的流程就分析完了，总结都在这个图上

喜欢的话就给个好评吧，你的肯定是我坚持写作最大的动力，来吧兄弟们，给我一点动力