前言:
眼前大家对“java赋值对象”大体比较珍视,各位老铁们都想要剖析一些“java赋值对象”的相关资讯。那么小编在网络上网罗了一些对于“java赋值对象””的相关知识,希望你们能喜欢,咱们一起来了解一下吧!目录
1. 属性赋值概述2. 流程概览3. 源码分析3.1 收集@PostConstruct @PreDestroy注解的方法3.2 收集@Resource注解的属性与方法3.3 @Autowired注解的属性与方法收集3.4 属性赋值4. 总结
每次进入源码的世界,就像完成一场奇妙的旅行!
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1. 属性赋值概述
上一篇讲述了bean实例化中的创建实例过程,实例化后就需要对类中的属性进行依赖注入操作,本篇将重点分析属性赋值相关流程。其中属性赋值,体现在AbstractAutowireCapableBeanFactory类中的doCreateBean方法中的populateBean(beanName, mbd, instanceWrapper)这行代码;在赋值之前还做了收集属性的相关操作,下面就通过源码来分析。
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2. 流程概览
流程中分为三步:
step1:通过BeanPostProcessor的实现类,实现了带注解的属性收集,CommonAnnotationBeanPostProcessor 支持了@PostContructor、@PreDestroy、@Resource的收集;AutowiredAnnotationBeanPostProcessor支持@Autowired、@value注解的属性收集;
step2:将收集有注解属性和方法封装到对应的容器中;
step3:遍历容器中的属性,注入到对应的bean实例中。
3. 源码分析3.1 收集@PostConstruct @PreDestroy注解的方法
首先AbstractAutowireCapableBeanFactory类中的doCreateBean`方法:
protected Object doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) throws BeanCreationException { // Instantiate the bean. BeanWrapper instanceWrapper = null; if (mbd.isSingleton()) { instanceWrapper = this.factoryBeanInstanceCache.remove(beanName); } if (instanceWrapper == null) { //创建对象实例 instanceWrapper = createBeanInstance(beanName, mbd, args); } Object bean = instanceWrapper.getWrappedInstance(); Class<?> beanType = instanceWrapper.getWrappedClass(); if (beanType != NullBean.class) { mbd.resolvedTargetType = beanType; } // Allow post-processors to modify the merged bean definition. synchronized (mbd.postProcessingLock) { if (!mbd.postProcessed) { try { // 收集注解 // BeanPostProcessor典型应用 // CommonAnnotationBeanPostProcessor 支持了@PostContructor @PreDestroy @Resource // AutowiredAnnotationBeanPostProcessor 支持@Autowired @value 注解 applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName); } catch (Throwable ex) { throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Post-processing of merged bean definition failed", ex); } mbd.postProcessed = true; } } // Eagerly cache singletons to be able to resolve circular references // even when triggered by lifecycle interfaces like BeanFactoryAware. boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences && isSingletonCurrentlyInCreation(beanName)); if (earlySingletonExposure) { if (logger.isTraceEnabled()) { logger.trace("Eagerly caching bean '" + beanName + "' to allow for resolving potential circular references"); } addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean)); } // Initialize the bean instance. Object exposedObject = bean; try { // 属性赋值 populateBean(beanName, mbd, instanceWrapper); // 初始化bean exposedObject = initializeBean(beanName, exposedObject, mbd); } catch (Throwable ex) { if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) { throw (BeanCreationException) ex; } else { throw new BeanCreationException( mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex); } } if (earlySingletonExposure) { Object earlySingletonReference = getSingleton(beanName, false); if (earlySingletonReference != null) { if (exposedObject == bean) { exposedObject = earlySingletonReference; } else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) { String[] dependentBeans = getDependentBeans(beanName); Set<String> actualDependentBeans = new LinkedHashSet<>(dependentBeans.length); for (String dependentBean : dependentBeans) { if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) { actualDependentBeans.add(dependentBean); } } if (!actualDependentBeans.isEmpty()) { throw new BeanCurrentlyInCreationException(beanName, "Bean with name '" + beanName + "' has been injected into other beans [" + StringUtils.collectionToCommaDelimitedString(actualDependentBeans) + "] in its raw version as part of a circular reference, but has eventually been " + "wrapped. This means that said other beans do not use the final version of the " + "bean. This is often the result of over-eager type matching - consider using " + "'getBeanNamesForType' with the 'allowEagerInit' flag turned off, for example."); } } } } // Register bean as disposable. try { registerDisposableBeanIfNecessary(beanName, bean, mbd); } catch (BeanDefinitionValidationException ex) { throw new BeanCreationException( mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex); } return exposedObject; }
createBeanInstance上一篇已经讲完,完成bean的创建,创建完后,bean只是在堆内存中申请了一块内存空间,还没有对其属性赋值,而在属性赋值前,优先收集标注了注解的属性,收集过程在applyMergedBeanDefinitionPostProcessors方法中完成,进入该方法:
protected void applyMergedBeanDefinitionPostProcessors(RootBeanDefinition mbd, Class<?> beanType, String beanName) { // 遍历当前类中的所有BeanPostProcessors for (BeanPostProcessor bp : getBeanPostProcessors()) { if (bp instanceof MergedBeanDefinitionPostProcessor) { MergedBeanDefinitionPostProcessor bdp = (MergedBeanDefinitionPostProcessor) bp; bdp.postProcessMergedBeanDefinition(mbd, beanType, beanName); } } }
遍历当前类中的实现了BeanPostProcessor接口的类,再次进入postProcessMergedBeanDefinition方法,会看到有几个典型的实现类,首先是 CommonAnnotationBeanPostProcessor类,这个类完成了@Resource注解的属性或者方法的收集,这个类还对@PostConstruct和@PreDestory支持。具体的收集过程如下:
public void postProcessMergedBeanDefinition(RootBeanDefinition beanDefinition, Class<?> beanType, String beanName) { // 扫描@PostConstructor @PreDestroy super.postProcessMergedBeanDefinition(beanDefinition, beanType, beanName); // 扫描属性与方法上的@Resource注解,收集到InjectionMetadata容器中 InjectionMetadata metadata = findResourceMetadata(beanName, beanType, null); metadata.checkConfigMembers(beanDefinition); }
回到CommonAnnotationBeanPostProcessor类的构造方法,完成@PostConstruct和@PreDestory注解的设置,分别塞到initAnnotationType与destroyAnnotationType属性中:
public CommonAnnotationBeanPostProcessor() { setOrder(Ordered.LOWEST_PRECEDENCE - 3); setInitAnnotationType(PostConstruct.class); setDestroyAnnotationType(PreDestroy.class); ignoreResourceType("javax.xml.ws.WebServiceContext"); }
点击进入其父类InitDestroyAnnotationBeanPostProcessor的postProcessMergedBeanDefinition方法
public void postProcessMergedBeanDefinition(RootBeanDefinition beanDefinition, Class<?> beanType, String beanName) { LifecycleMetadata metadata = findLifecycleMetadata(beanType); metadata.checkConfigMembers(beanDefinition); }
点击findLifecycleMetadata进入方法:
private LifecycleMetadata findLifecycleMetadata(Class<?> clazz) { if (this.lifecycleMetadataCache == null) { // Happens after deserialization, during destruction... return buildLifecycleMetadata(clazz); } // Quick check on the concurrent map first, with minimal locking. LifecycleMetadata metadata = this.lifecycleMetadataCache.get(clazz); if (metadata == null) { synchronized (this.lifecycleMetadataCache) { metadata = this.lifecycleMetadataCache.get(clazz); if (metadata == null) { // 构建生命周期相关的元数据 metadata = buildLifecycleMetadata(clazz); this.lifecycleMetadataCache.put(clazz, metadata); } return metadata; } } return metadata; }
再次进入构建生命周期相关的元数据的方法buildLifecycleMetadata:
private LifecycleMetadata buildLifecycleMetadata(final Class<?> clazz) { if (!AnnotationUtils.isCandidateClass(clazz, Arrays.asList(this.initAnnotationType, this.destroyAnnotationType))) { return this.emptyLifecycleMetadata; } List<LifecycleElement> initMethods = new ArrayList<>(); List<LifecycleElement> destroyMethods = new ArrayList<>(); Class<?> targetClass = clazz; do { final List<LifecycleElement> currInitMethods = new ArrayList<>(); final List<LifecycleElement> currDestroyMethods = new ArrayList<>(); //遍历类中的方法,找到@PostConstruct注解的方法 ReflectionUtils.doWithLocalMethods(targetClass, method -> { if (this.initAnnotationType != null && method.isAnnotationPresent(this.initAnnotationType)) { LifecycleElement element = new LifecycleElement(method); currInitMethods.add(element); if (logger.isTraceEnabled()) { logger.trace("Found init method on class [" + clazz.getName() + "]: " + method); } } //遍历类中的方法,找到@PreDestroy注解的方法 if (this.destroyAnnotationType != null && method.isAnnotationPresent(this.destroyAnnotationType)) { currDestroyMethods.add(new LifecycleElement(method)); if (logger.isTraceEnabled()) { logger.trace("Found destroy method on class [" + clazz.getName() + "]: " + method); } } }); // @PostConstruct注解的方法加到initMethods initMethods.addAll(0, currInitMethods); // @PreDestroy注解的方法加到destroyMethods destroyMethods.addAll(currDestroyMethods); targetClass = targetClass.getSuperclass(); } while (targetClass != null && targetClass != Object.class); return (initMethods.isEmpty() && destroyMethods.isEmpty() ? this.emptyLifecycleMetadata : new LifecycleMetadata(clazz, initMethods, destroyMethods)); }
循环遍历类中的所有的方法,判断方法上是否有@PostConstruct注解如果有的话加入到initMethods集合,判断方法上是否有@PreDestroy注解,如果有加入到destroyMethods集合中去。
3.2 收集@Resource注解的属性与方法
进入上述findResourceMetadata方法:
private InjectionMetadata findResourceMetadata(String beanName, final Class<?> clazz, @Nullable PropertyValues pvs) { // Fall back to class name as cache key, for backwards compatibility with custom callers. String cacheKey = (StringUtils.hasLength(beanName) ? beanName : clazz.getName()); // 查看缓存里面有没有InjectionMetadata实例. InjectionMetadata metadata = this.injectionMetadataCache.get(cacheKey); if (InjectionMetadata.needsRefresh(metadata, clazz)) { synchronized (this.injectionMetadataCache) { metadata = this.injectionMetadataCache.get(cacheKey); if (InjectionMetadata.needsRefresh(metadata, clazz)) { if (metadata != null) { metadata.clear(pvs); } // 构建@Resource元数据 metadata = buildResourceMetadata(clazz); this.injectionMetadataCache.put(cacheKey, metadata); } } } return metadata; }
step1:看缓存里面有没有 InjectionMetadata 对象;
step2:构建@Resource元数据;
再次进入buildResourceMetadata方法:
private InjectionMetadata buildResourceMetadata(final Class<?> clazz) { if (!AnnotationUtils.isCandidateClass(clazz, resourceAnnotationTypes)) { return InjectionMetadata.EMPTY; } List<InjectionMetadata.InjectedElement> elements = new ArrayList<>(); Class<?> targetClass = clazz; do { final List<InjectionMetadata.InjectedElement> currElements = new ArrayList<>(); // 遍历所有field,判断有没有Resource注解 ReflectionUtils.doWithLocalFields(targetClass, field -> { if (webServiceRefClass != null && field.isAnnotationPresent(webServiceRefClass)) { if (Modifier.isStatic(field.getModifiers())) { throw new IllegalStateException("@WebServiceRef annotation is not supported on static fields"); } currElements.add(new WebServiceRefElement(field, field, null)); } else if (ejbClass != null && field.isAnnotationPresent(ejbClass)) { if (Modifier.isStatic(field.getModifiers())) { throw new IllegalStateException("@EJB annotation is not supported on static fields"); } currElements.add(new EjbRefElement(field, field, null)); } else if (field.isAnnotationPresent(Resource.class)) { if (Modifier.isStatic(field.getModifiers())) { throw new IllegalStateException("@Resource annotation is not supported on static fields"); } if (!this.ignoredResourceTypes.contains(field.getType().getName())) { currElements.add(new ResourceElement(field, field, null)); } } }); // 遍历所有方法,判断有没有@Resource注解 ReflectionUtils.doWithLocalMethods(targetClass, method -> { Method bridgedMethod = BridgeMethodResolver.findBridgedMethod(method); if (!BridgeMethodResolver.isVisibilityBridgeMethodPair(method, bridgedMethod)) { return; } if (method.equals(ClassUtils.getMostSpecificMethod(method, clazz))) { if (webServiceRefClass != null && bridgedMethod.isAnnotationPresent(webServiceRefClass)) { if (Modifier.isStatic(method.getModifiers())) { throw new IllegalStateException("@WebServiceRef annotation is not supported on static methods"); } if (method.getParameterCount() != 1) { throw new IllegalStateException("@WebServiceRef annotation requires a single-arg method: " + method); } PropertyDescriptor pd = BeanUtils.findPropertyForMethod(bridgedMethod, clazz); currElements.add(new WebServiceRefElement(method, bridgedMethod, pd)); } else if (ejbClass != null && bridgedMethod.isAnnotationPresent(ejbClass)) { if (Modifier.isStatic(method.getModifiers())) { throw new IllegalStateException("@EJB annotation is not supported on static methods"); } if (method.getParameterCount() != 1) { throw new IllegalStateException("@EJB annotation requires a single-arg method: " + method); } PropertyDescriptor pd = BeanUtils.findPropertyForMethod(bridgedMethod, clazz); currElements.add(new EjbRefElement(method, bridgedMethod, pd)); } else if (bridgedMethod.isAnnotationPresent(Resource.class)) { if (Modifier.isStatic(method.getModifiers())) { throw new IllegalStateException("@Resource annotation is not supported on static methods"); } Class<?>[] paramTypes = method.getParameterTypes(); if (paramTypes.length != 1) { throw new IllegalStateException("@Resource annotation requires a single-arg method: " + method); } if (!this.ignoredResourceTypes.contains(paramTypes[0].getName())) { PropertyDescriptor pd = BeanUtils.findPropertyForMethod(bridgedMethod, clazz); currElements.add(new ResourceElement(method, bridgedMethod, pd)); } } } }); elements.addAll(0, currElements); targetClass = targetClass.getSuperclass(); } while (targetClass != null && targetClass != Object.class); return InjectionMetadata.forElements(elements, clazz); }
step1:从类中获取所有 Field 对象,循环 field 对象,判断 field 有没有@Resource 注解,如果有注解封装成 ResourceElement 对象;
step2:从类中获取所有 Method对象,循环 Method对象,判断 Method有没有@Resource 注解,如果有注解封装成 ResourceElement 对象;
step3:最终把两个 field 和 Method 封装的对象集合封装到 InjectionMetadata 对象中。
3.3 @Autowired注解的属性与方法收集
AutowiredAnnotationBeanPostProcessor类对@Autowired和@Value注解的属性和方法的收集,收集支持的注解类型可以在构造函数或者 Static 静态块中找。收集过程基本上跟@Resource注解的收集差不多。下面先看AutowiredAnnotationBeanPostProcessor的构造函数:
public AutowiredAnnotationBeanPostProcessor() { this.autowiredAnnotationTypes.add(Autowired.class); this.autowiredAnnotationTypes.add(Value.class); try { this.autowiredAnnotationTypes.add((Class<? extends Annotation>) ClassUtils.forName("javax.inject.Inject", AutowiredAnnotationBeanPostProcessor.class.getClassLoader())); logger.trace("JSR-330 'javax.inject.Inject' annotation found and supported for autowiring"); } catch (ClassNotFoundException ex) { // JSR-330 API not available - simply skip. } }
收集了@Autowired和@Value注解并设置到autowiredAnnotationTypes类型中。后面流程与@Resource收集一样,也是收集Field和Method上面的注解,然后放到InjectionMetadata对象中。
private InjectionMetadata buildAutowiringMetadata(final Class<?> clazz) { if (!AnnotationUtils.isCandidateClass(clazz, this.autowiredAnnotationTypes)) { return InjectionMetadata.EMPTY; } List<InjectionMetadata.InjectedElement> elements = new ArrayList<>(); Class<?> targetClass = clazz; do { final List<InjectionMetadata.InjectedElement> currElements = new ArrayList<>(); // 循环收集Field上面是否有@Autowired注解 ReflectionUtils.doWithLocalFields(targetClass, field -> { MergedAnnotation<?> ann = findAutowiredAnnotation(field); if (ann != null) { if (Modifier.isStatic(field.getModifiers())) { if (logger.isInfoEnabled()) { logger.info("Autowired annotation is not supported on static fields: " + field); } return; } boolean required = determineRequiredStatus(ann); currElements.add(new AutowiredFieldElement(field, required)); } }); // 循环收集Method上面是否有@Autowired注解 ReflectionUtils.doWithLocalMethods(targetClass, method -> { Method bridgedMethod = BridgeMethodResolver.findBridgedMethod(method); if (!BridgeMethodResolver.isVisibilityBridgeMethodPair(method, bridgedMethod)) { return; } MergedAnnotation<?> ann = findAutowiredAnnotation(bridgedMethod); if (ann != null && method.equals(ClassUtils.getMostSpecificMethod(method, clazz))) { if (Modifier.isStatic(method.getModifiers())) { if (logger.isInfoEnabled()) { logger.info("Autowired annotation is not supported on static methods: " + method); } return; } if (method.getParameterCount() == 0) { if (logger.isInfoEnabled()) { logger.info("Autowired annotation should only be used on methods with parameters: " + method); } } boolean required = determineRequiredStatus(ann); PropertyDescriptor pd = BeanUtils.findPropertyForMethod(bridgedMethod, clazz); currElements.add(new AutowiredMethodElement(method, required, pd)); } }); // 放入容器elements,而elements本身是InjectionMetadata类型下的InjectedElement属性 elements.addAll(0, currElements); targetClass = targetClass.getSuperclass(); } while (targetClass != null && targetClass != Object.class); return InjectionMetadata.forElements(elements, clazz); }3.4 属性赋值
收集完@Resource和@Autowired注解以后就开始依赖注入,进入populateBean方法:
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. if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) { for (BeanPostProcessor bp : getBeanPostProcessors()) { if (bp instanceof InstantiationAwareBeanPostProcessor) { InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp; if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) { 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; // 依赖注入的过程,@Autowired支持 @Resource支持 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); } }
该方法的核心工作就是完成依赖注入,进入postProcessProperties方法:
public PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName) { InjectionMetadata metadata = findAutowiringMetadata(beanName, bean.getClass(), pvs); try { // 依赖注入 metadata.inject(bean, beanName, pvs); } catch (BeanCreationException ex) { throw ex; } catch (Throwable ex) { throw new BeanCreationException(beanName, "Injection of autowired dependencies failed", ex); } return pvs; }
最后通过metadata.inject方法把容器中收集的属性注入:
public void inject(Object target, @Nullable String beanName, @Nullable PropertyValues pvs) throws Throwable { Collection<InjectedElement> checkedElements = this.checkedElements; Collection<InjectedElement> elementsToIterate = (checkedElements != null ? checkedElements : this.injectedElements); if (!elementsToIterate.isEmpty()) { for (InjectedElement element : elementsToIterate) { if (logger.isTraceEnabled()) { logger.trace("Processing injected element of bean '" + beanName + "': " + element); } // 循环调用每个方法依赖一次处理 element.inject(target, beanName, pvs); } } }
点击进入inject方法:
protected void inject(Object target, @Nullable String requestingBeanName, @Nullable PropertyValues pvs) throws Throwable { if (this.isField) { Field field = (Field) this.member; ReflectionUtils.makeAccessible(field); // 设置属性,getResourceToInject会触发getBean field.set(target, getResourceToInject(target, requestingBeanName)); } else { if (checkPropertySkipping(pvs)) { return; } try { Method method = (Method) this.member; ReflectionUtils.makeAccessible(method); // 设置方法 method.invoke(target, getResourceToInject(target, requestingBeanName)); } catch (InvocationTargetException ex) { throw ex.getTargetException(); } } }
看到属性与方法通过反射地注入到所需的实例中,如果注入的是引用类型,会通过调用getResourceToInject方法优先拿到引用类型的实例,底层是通过BeanFactory.getBean方式拿到应用的属性的:
protected Object getResourceToInject(Object target, @Nullable String requestingBeanName) { if (StringUtils.hasLength(this.beanName)) { if (beanFactory != null && beanFactory.containsBean(this.beanName)) { // Local match found for explicitly specified local bean name. // 通过getBean方式拿引用类型的值 Object bean = beanFactory.getBean(this.beanName, this.lookupType); if (requestingBeanName != null && beanFactory instanceof ConfigurableBeanFactory) { ((ConfigurableBeanFactory) beanFactory).registerDependentBean(this.beanName, requestingBeanName); } return bean; } else if (this.isDefaultName && !StringUtils.hasLength(this.mappedName)) { throw new NoSuchBeanDefinitionException(this.beanName, "Cannot resolve 'beanName' in local BeanFactory. Consider specifying a general 'name' value instead."); } }4. 总结
本篇讲述了实例化后属性的收集与赋值过程,通过典型的BeanPostProccessor应用,完成相关注解的收集,并完成依赖注入,最终完成属性赋值,后续将继续分析初始化流程。
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