BeanFactory後置處理器 - ConfigurationClassPostProcessor#postProcessBeanFactory
demo和springIOC - ConfigurationClassPostProcessor - full / lite裡面是同一個.
暫且先不管 full , lite 有什麼作用, 也不管spring是如何做到的, 如果是自己做, 怎麼可以實現那種效果.
demo:
public class Parent { public IndexDao1 indexDao1() { System.out.println("parent indexDao1"); return new IndexDao1(); } public IndexDao2 indexDao2() { System.out.println("parent indexDao2"); indexDao1(); return new IndexDao2(); } }
這裡, 我有兩個方法 indexDao1 和 indexDao2, 方法indexDao2中呼叫了 indexDao1方法. 現在這種情況, 會導致 IndexDao1 被建立兩次.
那麼通過什麼辦法, 可以讓 IndexDao1 只建立一次呢?
方法一:
再寫一個類Son, 來繼承 Parent 類, 然後通過 重寫他的 indexDao1 和 indexDao2 方法來改變他們的行為.
同時, 我還需要引入一個map, 來儲存建立的物件. 在執行方法之前, 先從map中獲取
-> 獲取到了, 則直接返回這個物件
-> 沒獲取到, 則執行父類中的方法, 來獲取物件, 存入 map 中.
public class Son extends Parent { Map<String , Object> map = new HashMap<>(); @Override public IndexDao1 indexDao1() { System.out.println("son indexDao1"); if(map.get("indexDao1") != null){return (IndexDao1) map.get("indexDao1"); } IndexDao1 indexDao1 = super.indexDao1(); map.put("indexDao1", indexDao1); return indexDao1; } @Override public IndexDao2 indexDao2() { System.out.println("son indexDao2"); //Parent中, 執行的 indexDao1() 已經被 Son 重寫, 所以會執行 Son 中的 indexDao1() if(map.get("indexDao2") != null){ return (IndexDao2) map.get("indexDao2"); } IndexDao2 indexDao2 = super.indexDao2(); map.put("indexDao2", indexDao2); return indexDao2; } }
測試程式碼:
public static void main(String[] args) { printf(); Son son = new Son(); son.indexDao1(); printf(); son.indexDao2(); } private static void printf(){ System.out.println("================"); }
結果:
方法二:
通過cglib代理的方式, 來建立一個繼承Parent的類也是可以達到效果的.
public class ParentMethodInceptor implements MethodInterceptor { Map<String, Object> map = new HashMap<>(); @Override public Object intercept(Object obj, Method method, Object[] args, MethodProxy methodProxy) throws Throwable { System.out.println("proxy --- " + method.getName()); if (map.get(method.getName()) != null) { return map.get(method.getName()); } Object res = methodProxy.invokeSuper(obj, args); map.put(method.getName(), res); return res; } }
測試程式碼:
public static void main(String[] args) { Enhancer enhancer = new Enhancer(); enhancer.setSuperclass(Parent.class); enhancer.setCallback(new ParentMethodInceptor()); Parent proxy = (Parent) enhancer.create(); printf(); proxy.indexDao1(); printf(); proxy.indexDao2(); } private static void printf(){ System.out.println("================"); }
結果:
如果 Parent 類中的 indexDao1 變成一個靜態方法: public static IndexDao1 indexDao1{}
那麼不管是方法一,還是方法二, 都是不能實現只建立一次的效果.
方法一 中, 不能對靜態方法進行重寫覆蓋
方法二 中, 不能對靜態方法進行代理
不過, 我測試過 spring , 他也是辦不到的, 也會建立兩次.
原始碼:
ConfigurationClassPostProcessor 的postProcessBeanDefinitionRegistry 呼叫結束之後,
就會呼叫他的postProcessBeanFactory 方法.
@Override public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) { int factoryId = System.identityHashCode(beanFactory); if (this.factoriesPostProcessed.contains(factoryId)) { throw new IllegalStateException( "postProcessBeanFactory already called on this post-processor against " + beanFactory); } this.factoriesPostProcessed.add(factoryId); if (!this.registriesPostProcessed.contains(factoryId)) { // BeanDefinitionRegistryPostProcessor hook apparently not supported... // Simply call processConfigurationClasses lazily at this point then. processConfigBeanDefinitions((BeanDefinitionRegistry) beanFactory); } //給配置類產生cglib代理 //為什麼需要產生cglib代理? enhanceConfigurationClasses(beanFactory); beanFactory.addBeanPostProcessor(new ImportAwareBeanPostProcessor(beanFactory)); }
除了產生了一次 cglib 代理外, 還向容器中註冊了一個後置處理器:ImportAwareBeanPostProcessor
這裡主要還是看這個 cglib 代理, 它是根據是否有 @Configuration 註解來判斷是否要進行的.
此例中, 主要是對 配置類 StartConfig 產生cglib代理的.
那麼為什麼要對 StartConfig 產生 cglib 代理呢?
是不是想要達到 上面 demo 中的效果呢? 讓 IndexDao1 只建立一遍?
public void enhanceConfigurationClasses(ConfigurableListableBeanFactory beanFactory) { Map<String, AbstractBeanDefinition> configBeanDefs = new LinkedHashMap<>();
//解析拿到容器中的配置類(加了@Configuration註解的), 放在 configBeanDefs 中 for (String beanName : beanFactory.getBeanDefinitionNames()) { BeanDefinition beanDef = beanFactory.getBeanDefinition(beanName); //判斷是否是一個全註解類 //掃描是全註解類?full和lite的關係 if (ConfigurationClassUtils.isFullConfigurationClass(beanDef)) { if (!(beanDef instanceof AbstractBeanDefinition)) { throw new BeanDefinitionStoreException("Cannot enhance @Configuration bean definition '" + beanName + "' since it is not stored in an AbstractBeanDefinition subclass"); } else if (logger.isInfoEnabled() && beanFactory.containsSingleton(beanName)) { logger.info("Cannot enhance @Configuration bean definition '" + beanName + "' since its singleton instance has been created too early. The typical cause " + "is a non-static @Bean method with a BeanDefinitionRegistryPostProcessor " + "return type: Consider declaring such methods as 'static'."); } configBeanDefs.put(beanName, (AbstractBeanDefinition) beanDef); } } if (configBeanDefs.isEmpty()) { // nothing to enhance -> return immediately return; } ConfigurationClassEnhancer enhancer = new ConfigurationClassEnhancer(); for (Map.Entry<String, AbstractBeanDefinition> entry : configBeanDefs.entrySet()) { AbstractBeanDefinition beanDef = entry.getValue(); // If a @Configuration class gets proxied, always proxy the target class beanDef.setAttribute(AutoProxyUtils.PRESERVE_TARGET_CLASS_ATTRIBUTE, Boolean.TRUE); try { // Set enhanced subclass of the user-specified bean class Class<?> configClass = beanDef.resolveBeanClass(this.beanClassLoader); if (configClass != null) { //完成對全註解類的cglib代理 Class<?> enhancedClass = enhancer.enhance(configClass, this.beanClassLoader); if (configClass != enhancedClass) { if (logger.isTraceEnabled()) { logger.trace(String.format("Replacing bean definition '%s' existing class '%s' with " + "enhanced class '%s'", entry.getKey(), configClass.getName(), enhancedClass.getName())); } beanDef.setBeanClass(enhancedClass); } } } catch (Throwable ex) { throw new IllegalStateException("Cannot load configuration class: " + beanDef.getBeanClassName(), ex); } } }
從上面這段程式碼來看, 只有載入了 @Configuration 的配置類, 才會進行cglib代理.
那前面的 full / lite 屬性設定的意義, 在這裡就體現出來了.
1. full 模式下, 會進行配置類的 cglib 代理.
2. lite模式下, 此處就直接返回了.
enhance
org.springframework.context.annotation.ConfigurationClassEnhancer#enhance
public Class<?> enhance(Class<?> configClass, @Nullable ClassLoader classLoader) { //判斷是否被代理過 if (EnhancedConfiguration.class.isAssignableFrom(configClass)) { if (logger.isDebugEnabled()) { logger.debug(String.format("Ignoring request to enhance %s as it has " + "already been enhanced. This usually indicates that more than one " + "ConfigurationClassPostProcessor has been registered (e.g. via " + "<context:annotation-config>). This is harmless, but you may " + "want check your configuration and remove one CCPP if possible", configClass.getName())); } return configClass; } //沒有被代理cglib代理 Class<?> enhancedClass = createClass(newEnhancer(configClass, classLoader)); if (logger.isTraceEnabled()) { logger.trace(String.format("Successfully enhanced %s; enhanced class name is: %s", configClass.getName(), enhancedClass.getName())); } return enhancedClass; }
EnhancedConfiguration
這裡通過 EnhancedConfiguration 來判斷, 配置類是否被代理過.
為什麼能這麼判斷呢?
org.springframework.context.annotation.ConfigurationClassEnhancer.EnhancedConfiguration
public interface EnhancedConfiguration extends BeanFactoryAware {}
看原始碼, 知道他是一個空介面, 啥也不幹.
如果在進行 cglib 代理的時候, 讓生成的動態代理類實現這個介面, 那麼就可以通過判斷配置類是否實現這個介面, 來確定是否被代理了.
newEnhancer
這裡做了建立代理類前的屬性配置
org.springframework.context.annotation.ConfigurationClassEnhancer#newEnhancer
private Enhancer newEnhancer(Class<?> configSuperClass, @Nullable ClassLoader classLoader) { Enhancer enhancer = new Enhancer(); //增強父類,cglib是基於繼承來的 enhancer.setSuperclass(configSuperClass); //增強介面,為什麼要增強介面? //便於判斷,表示一個類以及被增強了 enhancer.setInterfaces(new Class<?>[] {EnhancedConfiguration.class}); //不繼承Factory介面 enhancer.setUseFactory(false); enhancer.setNamingPolicy(SpringNamingPolicy.INSTANCE); // BeanFactoryAwareGeneratorStrategy是一個生成策略 // 主要為生成的CGLIB類中新增成員變數$$beanFactory // 同時基於介面EnhancedConfiguration的父介面BeanFactoryAware中的setBeanFactory方法, // 設定此變數的值為當前Context中的beanFactory,這樣一來我們這個cglib代理的物件就有了beanFactory //有了factory就能獲得物件,而不用去通過方法獲得物件了,因為通過方法獲得物件不能控制器過程 //該BeanFactory的作用是在this呼叫時攔截該呼叫,並直接在beanFactory中獲得目標bean enhancer.setStrategy(new BeanFactoryAwareGeneratorStrategy(classLoader)); //過濾方法,不能每次都去new enhancer.setCallbackFilter(CALLBACK_FILTER); enhancer.setCallbackTypes(CALLBACK_FILTER.getCallbackTypes()); return enhancer; }
從這段程式碼看, spring確實是, 將 EnhancedConfiguration 放到了動態代理類中. 讓動態代理類實現它.
createClass
正式建立代理類, 設定 MethodInterceptor
org.springframework.context.annotation.ConfigurationClassEnhancer#createClass
private Class<?> createClass(Enhancer enhancer) { Class<?> subclass = enhancer.createClass(); // Registering callbacks statically (as opposed to thread-local) // is critical for usage in an OSGi environment (SPR-5932)... Enhancer.registerStaticCallbacks(subclass, CALLBACKS); return subclass; }
org.springframework.context.annotation.ConfigurationClassEnhancer#CALLBACKS
private static final Callback[] CALLBACKS = new Callback[] { //增強方法,主要控制 bean 的作用域 //不每一次都去呼叫new new BeanMethodInterceptor(), //設定一個beanFactory new BeanFactoryAwareMethodInterceptor(), NoOp.INSTANCE };
BeanMethodInterceptor實現了MethodInterceptor
熟悉cglib的應該知道, 他是一個方法攔截器, 會對被代理的目標方法進行攔截包裝.
其效果跟 上面demo中的方法二一樣. 可以改變目標方法的邏輯
BeanMethodInterceptor
public Object intercept(Object enhancedConfigInstance, Method beanMethod, Object[] beanMethodArgs, MethodProxy cglibMethodProxy) throws Throwable { //enhancedConfigInstance 代理 // 通過enhancedConfigInstance中cglib生成的成員變數$$beanFactory獲得beanFactory。 ConfigurableBeanFactory beanFactory = getBeanFactory(enhancedConfigInstance); String beanName = BeanAnnotationHelper.determineBeanNameFor(beanMethod); // Determine whether this bean is a scoped-proxy if (BeanAnnotationHelper.isScopedProxy(beanMethod)) { String scopedBeanName = ScopedProxyCreator.getTargetBeanName(beanName); if (beanFactory.isCurrentlyInCreation(scopedBeanName)) { beanName = scopedBeanName; } } // To handle the case of an inter-bean method reference, we must explicitly check the // container for already cached instances. // First, check to see if the requested bean is a FactoryBean. If so, create a subclass // proxy that intercepts calls to getObject() and returns any cached bean instance. // This ensures that the semantics of calling a FactoryBean from within @Bean methods // is the same as that of referring to a FactoryBean within XML. See SPR-6602. if (factoryContainsBean(beanFactory, BeanFactory.FACTORY_BEAN_PREFIX + beanName) && factoryContainsBean(beanFactory, beanName)) { Object factoryBean = beanFactory.getBean(BeanFactory.FACTORY_BEAN_PREFIX + beanName); if (factoryBean instanceof ScopedProxyFactoryBean) { // Scoped proxy factory beans are a special case and should not be further proxied } else { // It is a candidate FactoryBean - go ahead with enhancement return enhanceFactoryBean(factoryBean, beanMethod.getReturnType(), beanFactory, beanName); } } //一個非常牛逼的判斷 //判斷到底是new 還是get //判斷執行的方法和呼叫方法是不是同一個方法 if (isCurrentlyInvokedFactoryMethod(beanMethod)) { // The factory is calling the bean method in order to instantiate and register the bean // (i.e. via a getBean() call) -> invoke the super implementation of the method to actually // create the bean instance. if (logger.isInfoEnabled() && BeanFactoryPostProcessor.class.isAssignableFrom(beanMethod.getReturnType())) { logger.info(String.format("@Bean method %s.%s is non-static and returns an object " + "assignable to Spring's BeanFactoryPostProcessor interface. This will " + "result in a failure to process annotations such as @Autowired, " + "@Resource and @PostConstruct within the method's declaring " + "@Configuration class. Add the 'static' modifier to this method to avoid " + "these container lifecycle issues; see @Bean javadoc for complete details.", beanMethod.getDeclaringClass().getSimpleName(), beanMethod.getName())); }
//呼叫父類的相應方法 return cglibMethodProxy.invokeSuper(enhancedConfigInstance, beanMethodArgs); } return resolveBeanReference(beanMethod, beanMethodArgs, beanFactory, beanName); }
isCurrentlyInvokedFactoryMethod
//org.springframework.context.annotation.ConfigurationClassEnhancer.BeanMethodInterceptor#isCurrentlyInvokedFactoryMethod private boolean isCurrentlyInvokedFactoryMethod(Method method) { Method currentlyInvoked = SimpleInstantiationStrategy.getCurrentlyInvokedFactoryMethod(); return (currentlyInvoked != null && method.getName().equals(currentlyInvoked.getName()) && Arrays.equals(method.getParameterTypes(), currentlyInvoked.getParameterTypes())); }
在上面的demo中, 判斷是否要執行建立過程的邏輯是: 從map中獲取物件, 有則不建立, 沒有則建立.
顯然, spring在這裡, 並不是這麼幹的.
執行 indexDao1() 時, 通過除錯可以知道, method 是indexDao1(), currentlyInvoked 也是 indexDao1().
執行 indexDao2() 時, 會進入此方法兩次, 第一次是對 indexDao2() 本身的攔截, 第二次是對 他呼叫的 indexDao1() 的攔截.
第一次時:method 是indexDao2(), currentlyInvoked 也是 indexDao2().
第二次時:method 是indexDao1(), 但是 currentlyInvoked 卻變成了 indexDao2().
從這裡可以看出, spring 是通過方法名, 來進行是否要走父類方法的判斷的.
resolveBeanReference
這裡是通過spring工廠來獲取物件的. 暫時可以理解成, 上面demo中的map.
private Object resolveBeanReference(Method beanMethod, Object[] beanMethodArgs, ConfigurableBeanFactory beanFactory, String beanName) { // The user (i.e. not the factory) is requesting this bean through a call to // the bean method, direct or indirect. The bean may have already been marked // as 'in creation' in certain autowiring scenarios; if so, temporarily set // the in-creation status to false in order to avoid an exception. //判斷他是否正在建立 boolean alreadyInCreation = beanFactory.isCurrentlyInCreation(beanName); try { if (alreadyInCreation) { beanFactory.setCurrentlyInCreation(beanName, false); } boolean useArgs = !ObjectUtils.isEmpty(beanMethodArgs); if (useArgs && beanFactory.isSingleton(beanName)) { // Stubbed null arguments just for reference purposes, // expecting them to be autowired for regular singleton references? // A safe assumption since @Bean singleton arguments cannot be optional... for (Object arg : beanMethodArgs) { if (arg == null) { useArgs = false; break; } } } //beanFactory.getBean 通過容器來拿 Object beanInstance = (useArgs ? beanFactory.getBean(beanName, beanMethodArgs) : beanFactory.getBean(beanName)); if (!ClassUtils.isAssignableValue(beanMethod.getReturnType(), beanInstance)) { // Detect package-protected NullBean instance through equals(null) check if (beanInstance.equals(null)) { if (logger.isDebugEnabled()) { logger.debug(String.format("@Bean method %s.%s called as bean reference " + "for type [%s] returned null bean; resolving to null value.", beanMethod.getDeclaringClass().getSimpleName(), beanMethod.getName(), beanMethod.getReturnType().getName())); } beanInstance = null; } else { String msg = String.format("@Bean method %s.%s called as bean reference " + "for type [%s] but overridden by non-compatible bean instance of type [%s].", beanMethod.getDeclaringClass().getSimpleName(), beanMethod.getName(), beanMethod.getReturnType().getName(), beanInstance.getClass().getName()); try { BeanDefinition beanDefinition = beanFactory.getMergedBeanDefinition(beanName); msg += " Overriding bean of same name declared in: " + beanDefinition.getResourceDescription(); } catch (NoSuchBeanDefinitionException ex) { // Ignore - simply no detailed message then. } throw new IllegalStateException(msg); } } Method currentlyInvoked = SimpleInstantiationStrategy.getCurrentlyInvokedFactoryMethod(); if (currentlyInvoked != null) { String outerBeanName = BeanAnnotationHelper.determineBeanNameFor(currentlyInvoked); beanFactory.registerDependentBean(beanName, outerBeanName); } return beanInstance; } finally { if (alreadyInCreation) { beanFactory.setCurrentlyInCreation(beanName, true); } } }