基于springboot bean的实例化过程和属性注入过程
目录
- bean的实例化过程和属性注入过程
- bean实例化流程说明
bean的实例化过程和属性注入过程
了解过springboot的加载流程的都知道springboot初始化bean都在refresh方法中。
这个方法代码如下:
// Prepare this context for refreshing. prepareRefresh(); // Tell the subclass to refresh the internal bean factory.新建beanFactory ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory(); // Prepare the bean factory for use in this context. prepareBeanFactory(beanFactory); try { // Allows post-processing of the bean factory in context subclasses. postProcessBeanFactory(beanFactory); // Invoke factory processors registered as beans in the context. // 加载实现beanFactoryPostProcessor的bean,bean定义的时候执行 invokeBeanFactoryPostProcessors(beanFactory); // Register bean processors that intercept bean creation. // 加载实现了beanPostProcessor,在bean实例化前、后执行 registerBeanPostProcessors(beanFactory); // Initialize message source for this context. initMessageSource(); // Initialize event multicaster for this context. initApplicationEventMulticaster(); // Initialize other special beans in specific context subclasses. onRefresh(); // Check for listener beans and register them. registerListeners(); // Instantiate all remaining (non-lazy-init) singletons. //实例化非懒加载的bean、bean封装、属性注入、注解注入(主要使用BeanPostProcessor或子类实现)等 finishBeanFactoryInitialization(beanFactory); // Last step: publish corresponding event. finishRefresh();
这里我们主要看下finishBeanfactoryInitialization方法。此方法实现了bean的实例和属性注入等。进入此方法的最后一行。
// Instantiate all remaining (non-lazy-init) singletons. beanFactory.preInstantiateSingletons();
注释写的很清楚,实例化剩余非懒加载的bean。此方法的实现是核心类DefaultLisListableBeanFactory实现。这个方法中有个判断:bean是否是beanFactory的实现类。
如果是则获取bean的时候会从beanFactory实现类的getObject中获取,我们重点看看getBean这个方法。
getBean是spring中最重要、最牛逼的方法之一,具体的逻辑是通过doGetBean方法处理的。
我们看下doGetBean方法,方法很长。我们分成几个部分去看。
1、先判断是否已经存在缓存中,代码如下:
if (sharedInstance != null && args == null) { if (logger.isDebugEnabled()) { if (isSingletonCurrentlyInCreation(beanName)) { logger.debug("Returning eagerly cached instance of singleton bean '" + beanName + "' that is not fully initialized yet - a consequence of a circular reference"); } else { logger.debug("Returning cached instance of singleton bean '" + beanName + "'"); } } bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
2、从父beanfactory中获取
BeanFactory parentBeanFactory = getParentBeanFactory(); if (parentBeanFactory != null && !containsBeanDefinition(beanName)) { // Not found -> check parent. String nameToLookup = originalBeanName(name); if (parentBeanFactory instanceof AbstractBeanFactory) { return ((AbstractBeanFactory) parentBeanFactory).doGetBean( nameToLookup, requiredType, args, typeCheckOnly); } else if (args != null) { // Delegation to parent with explicit args. return (T) parentBeanFactory.getBean(nameToLookup, args); } else { // No args -> delegate to standard getBean method. return parentBeanFactory.getBean(nameToLookup, requiredType); } }
3、直接创建RootBeanDefinition
//mark 给此bean 马克一下。防止重复创建 if (!typeCheckOnly) { markBeanAsCreated(beanName); } try { final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName); checkMergedBeanDefinition(mbd, beanName, args); // Guarantee initialization of beans that the current bean depends on. String[] dependsOn = mbd.getDependsOn(); if (dependsOn != null) { for (String dep : dependsOn) { if (isDependent(beanName, dep)) { throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Circular depends-on relationship between '" + beanName + "' and '" + dep + "'"); } registerDependentBean(dep, beanName); getBean(dep); } }
4、是singleton还是prototype类型的,根据不同类型去实例化bean,代码只贴了单例的类型:
// Create bean instance. if (mbd.isSingleton()) { sharedInstance = getSingleton(beanName, () -> { try { return createBean(beanName, mbd, args); } catch (BeansException ex) { // Explicitly remove instance from singleton cache: It might have been put there // eagerly by the creation process, to allow for circular reference resolution. // Also remove any beans that received a temporary reference to the bean. destroySingleton(beanName); throw ex; } }); bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
5、检查bean的类型是否匹配
// Check if required type matches the type of the actual bean instance. if (requiredType != null && !requiredType.isInstance(bean)) { try { T convertedBean = getTypeConverter().convertIfNecessary(bean, requiredType); if (convertedBean == null) { throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass()); } return convertedBean; } catch (TypeMismatchException ex) { if (logger.isDebugEnabled()) { logger.debug("Failed to convert bean '" + name + "' to required type '" + ClassUtils.getQualifiedName(requiredType) + "'", ex); } throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass()); } }
整个doGetBean方法改成这5个部分,重点看下第4个部分中的createBean和getObjectForBeanInstance方法。
1、createBean方法,里面主要是2个部分,bean直接是通过BeanPostProcessor的postProcessBeforeIntantiation方法获取的。
注释也是描述的很清楚:Give BeanPostProcessors a chance to return a proxy instead of the bean instance(英语渣渣不敢瞎翻译误导大家,理解就好)
代码如下:
try { // Give BeanPostProcessors a chance to return a proxy instead of the target bean instance. Object bean = resolveBeforeInstantiation(beanName, mbdToUse); if (bean != null) { return bean; } } catch (Throwable ex) { throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName, "BeanPostProcessor before instantiation of bean failed", ex); }
第一个部分自己实现,那么createBean方法第2个部分毋庸置疑肯定是spring去实例化bean,代码如下:
try { Object beanInstance = doCreateBean(beanName, mbdToUse, args); if (logger.isDebugEnabled()) { logger.debug("Finished creating instance of bean '" + beanName + "'"); } return beanInstance; }
又是do开头的方法,说明这个也是一个创建方法,spring中一般do开头的都是用于创建某个对象。跟着代码走,看下doCreateBean方法,在查看此方法之前,可能需要了解下BeanWarpper这个封装类。bean的封装、属性注入等都是用BeanWarpper去完成的。
看下代码:
// Instantiate the bean. BeanWrapper instanceWrapper = null; if (mbd.isSingleton()) { instanceWrapper = this.factoryBeanInstanceCache.remove(beanName); } if (instanceWrapper == null) { instanceWrapper = createBeanInstance(beanName, mbd, args); }
进入createBeanInstance方法中,就是调用构造器去实例化bean,返回beanWrapper。通过构造器获取实例代码如下:
// Need to determine the constructor... Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName); if (ctors != null || mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_CONSTRUCTOR || mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) { return autowireConstructor(beanName, mbd, ctors, args); } // No special handling: simply use no-arg constructor. return instantiateBean(beanName, mbd);
这里实例化我一开始以为就是简单的反射,后面我点进去时候发现里面一直提策略实例化,我目前了解的是可以解决Override的问题等。如果有兴趣的可以自行查看。到这里为止。我们终于实例化bean了。下面看下第二步bean的属性注入等。
代码如下:
Object exposedObject = bean; try { populateBean(beanName, mbd, instanceWrapper); 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); } }
populateBean方法名称就暴露他是干啥的:填充bean。我放一段比较重要的部分:
if (hasInstAwareBpps || needsDepCheck) { if (pvs == null) { pvs = mbd.getPropertyValues(); } PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching); 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); } }
这段代码貌似没有什么注入、填充什么的,我们看下InstantiationAwareBeanPostProcessor这个接口,发现这个接口有个很熟悉的实现类是:AutowiredAnnotationBeanPostProcessor。这个类的方法中我们看到终于看到了jnject方法。但是在inject之前需要调用下findAutowiringMatedata方法获取一下元数据:
// Fall back to class name as cache key, for backwards compatibility with custom callers. String cacheKey = (StringUtils.hasLength(beanName) ? beanName : clazz.getName()); // Quick check on the concurrent map first, with minimal locking. 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); } metadata = buildAutowiringMetadata(clazz); this.injectionMetadataCache.put(cacheKey, metadata); } } } return metadata;
那么问题又来了,这个injectionMetadataCache集合值是从那里来的呢?AutowiredAnnotationBeanPostProcessor实现了MergeBeandefinitionPostProcessor,那么就好了,肯定是在bean实例的时候调用了postProcessMergedBeanDefintion这个方法。
果然在doCreateBean方法中有这么一段:
// Allow post-processors to modify the merged bean definition. synchronized (mbd.postProcessingLock) { if (!mbd.postProcessed) { try { //通过 BeanPostProcessor将需要注解的元数据 放到Map中 applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName); } catch (Throwable ex) { throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Post-processing of merged bean definition failed", ex); } mbd.postProcessed = true; } }
哎,spring缜密啊。元数据有了,下面我们看下element.inject()方法是如何操作的:
if (this.isField) { Field field = (Field) this.member; ReflectionUtils.makeAccessible(field); field.set(target, getResourceToInject(target, requestingBeanName)); } else { if (checkPropertySkipping(pvs)) { return; } try { Method method = (Method) this.member; ReflectionUtils.makeAccessible(method); method.invoke(target, getResourceToInject(target, requestingBeanName)); } catch (InvocationTargetException ex) { throw ex.getTargetException(); } }
方法简单明了,直接使用反射将值set到属性中,至此 bean的实例、属性注入基本完成,下面我们回头来看doGetBean的另一个方法getObjectForBeanInstance。
2、getObjectForBeanInstance方法。对于是FactoryBean类型的 bean通过getObject获取到bean的代理实例,跟着方法一直走下去会到getObejct()方法中。
if (System.getSecurityManager() != null) { AccessControlContext acc = getAccessControlContext(); try { object = AccessController.doPrivileged((PrivilegedExceptionAction<Object>) factory::getObject, acc); } catch (PrivilegedActionException pae) { throw pae.getException(); } } else { //从FactoryBean实现bean中getObejct获取到bean object = factory.getObject(); }
到此 finishBeanfactoryInitialization方法执行结束!
bean实例化流程说明
bean实例化流程流程是在onRefresh方法的finishBeanFactoryInitialization中。进入该方法
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) { // Initialize conversion service for this context. if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) && beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) { beanFactory.setConversionService( beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)); } // Register a default embedded value resolver if no bean post-processor // (such as a PropertyPlaceholderConfigurer bean) registered any before: // at this point, primarily for resolution in annotation attribute values. if (!beanFactory.hasEmbeddedValueResolver()) { beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal)); } // Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early. String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false); for (String weaverAwareName : weaverAwareNames) { getBean(weaverAwareName); } // Stop using the temporary ClassLoader for type matching. beanFactory.setTempClassLoader(null); // Allow for caching all bean definition metadata, not expecting further changes. beanFactory.freezeConfiguration(); // Instantiate all remaining (non-lazy-init) singletons. beanFactory.preInstantiateSingletons(); }
1、beanFactory.freezeConfiguration(); 标记正在实例化
当前有183个bean正在实例化中。
2、调用beanFactory.preInstantiateSingletons(); 实例化bean
以上为个人经验,希望能给大家一个参考,也希望大家多多支持我们。