Spring源碼之Spring后置處理器詳解

本文轉載自查看原文 2020-06-07 17:46 2773 spring源碼學習

什么是Spring的后置處理器？

　　Spring的后置處理器貫穿了整個springBean的實例化前后。

Spring后置處理器都有哪些類，哪些方法？

　　一.InstantiationAwareBeanPostProcessor

　　InstantiationAwareBeanPostProcessor接口繼承BeanPostProcessor接口，它內部提供了3個方法，再加上BeanPostProcessor接口內部的2個方法，所以實現這個接口需要實現5個方法。InstantiationAwareBeanPostProcessor接口的主要作用在於目標對象的實例化過程中需要處理的事情，包括實例化對象的前后過程以及實例的屬性設置在org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#createBean()方法的Object bean = resolveBeforeInstantiation(beanName, mbdToUse);方法里面執行了這個后置處理器。

　　1、postProcessBeforeInstantiation

　　在目標對象實例化之前調用，方法的返回值類型是Object，我們可以返回任何類型的值。由於這個時候目標對象還未實例化，所以這個返回值可以用來代替原本該生成的目標對象的實例(一般都是代理對象)。如果該方法的返回值代替原本該生成的目標對象，后續只有postProcessAfterInitialization方法會調用，其它方法不再調用；否則按照正常的流程走。

　　2、postProcessAfterInstantiation

　　方法在目標對象實例化之后調用，這個時候對象已經被實例化，但是該實例的屬性還未被設置，都是null。如果該方法返回false，會忽略屬性值的設置；如果返回true，會按照正常流程設置。

　　3、postProcessPropertyValues

　　方法對屬性值進行修改(這個時候屬性值還未被設置，但是我們可以修改原本該設置進去的屬性值)。如果postProcessAfterInstantiation方法返回false，該方法不會被調用。可以在該方法內對屬性值進行修改。

　　4、postProcessBeforeInitialization&postProcessAfterInitialization

　　父接口BeanPostProcessor的2個方法postProcessBeforeInitialization和postProcessAfterInitialization都是在目標對象被實例化之后，並且屬性也被設置之后調用的。

　　二、SmartInstantiationAwareBeanPostProcessor

　　智能實例化Bean后置處理器（繼承InstantiationAwareBeanPostProcessor）

　　1、determineCandidateConstructors

　　檢測Bean的構造器，可以檢測出多個候選構造器。

　　2、getEarlyBeanReference

　　循環引用的后置處理器，這個東西比較復雜，獲得提前暴露的bean引用。主要用於解決循環引用的問題，只有單例對象才會調用此方法。

　　3、predictBeanType

　　預測bean的類型。

　　三、MergedBeanDefinitionPostProcessor

　　1、postProcessMergedBeanDefinition

　　緩存bean的注入信息的后置處理器，僅僅是緩存或者干脆叫做查找更加合適，沒有完成注入，注入是另外一個后置處理器的作用。

Spring后置處理器源碼展現：

　　第一次執行后置處理器：

　　代碼路徑：org/springframework/beans/factory/support/AbstractAutowireCapableBeanFactory.java

　　　　　　AbstractAutowireCapableBeanFactory.createBean()--resolveBeforeInstantiation() ---這里是springbean的生命周期開始的地方

　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　-applyBeanPostProcessorsBeforeInstantiation()

　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　--applyBeanPostProcessorsAfterInitialization()

 1 protected Object resolveBeforeInstantiation(String beanName, RootBeanDefinition mbd) {
 2         Object bean = null;
 3         if (!Boolean.FALSE.equals(mbd.beforeInstantiationResolved)) {
 4             // Make sure bean class is actually resolved at this point.
 5             if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
 6                 Class<?> targetType = determineTargetType(beanName, mbd);
 7                 if (targetType != null) {
 8                     // 第一個后置處理器執行
 9                     bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName);
10                     if (bean != null) {
11                         bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
12                     }
13                 }
14             }
15             mbd.beforeInstantiationResolved = (bean != null);
16         }
17         return bean;
18     }

applyBeanPostProcessorsBeforeInstantiation()：

 1 protected Object applyBeanPostProcessorsBeforeInstantiation(Class<?> beanClass, String beanName) {
 2         //getBeanPostProcessors:拿到容器中所有實現了BeanPostProcessors接口的類
 3         for (BeanPostProcessor bp : getBeanPostProcessors()) {
 4             if (bp instanceof InstantiationAwareBeanPostProcessor) {
 5                 //第一個后置處理器
 6                 InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
 7                 Object result = ibp.postProcessBeforeInstantiation(beanClass, beanName);
 8                 if (result != null) {
 9                     return result;
10                 }
11             }
12         }
13         return null;
14     }

InstantiationAwareBeanPostProcessor.postProcessBeforeInstantiation();

　　第二次執行后置處理器：

　　　　代碼路徑：org/springframework/beans/factory/support/AbstractAutowireCapableBeanFactory.java

　　　　　　　　　AbstractAutowireCapableBeanFactory.createBeanInstance()--Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);---第二次執行后置處理器使用的地方
　　　　SmartInstantiationAwareBeanPostProcessor.determineCandidateConstructors()

 1 protected Constructor<?>[] determineConstructorsFromBeanPostProcessors(@Nullable Class<?> beanClass, String beanName)
 2             throws BeansException {
 3 
 4         if (beanClass != null && hasInstantiationAwareBeanPostProcessors()) {
 5             for (BeanPostProcessor bp : getBeanPostProcessors()) {
 6                 if (bp instanceof SmartInstantiationAwareBeanPostProcessor) {
 7                     SmartInstantiationAwareBeanPostProcessor ibp = (SmartInstantiationAwareBeanPostProcessor) bp;
 8                     Constructor<?>[] ctors = ibp.determineCandidateConstructors(beanClass, beanName);
 9                     if (ctors != null) {
10                         return ctors;
11                     }
12                 }
13             }
14         }
15         return null;
16     }

SmartInstantiationAwareBeanPostProcessor.determineCandidateConstructors()

第三次執行后置處理器：

　　代碼路徑：org/springframework/beans/factory/support/AbstractAutowireCapableBeanFactory.java

　　AbstractAutowireCapableBeanFactory.applyMergedBeanDefinitionPostProcessors()---第三次執行后置處理器

1 protected void applyMergedBeanDefinitionPostProcessors(RootBeanDefinition mbd, Class<?> beanType, String beanName) {
2         for (BeanPostProcessor bp : getBeanPostProcessors()) {
3             if (bp instanceof MergedBeanDefinitionPostProcessor) {
4                 MergedBeanDefinitionPostProcessor bdp = (MergedBeanDefinitionPostProcessor) bp;
5                 bdp.postProcessMergedBeanDefinition(mbd, beanType, beanName);
6             }
7         }
8     }

　　org/springframework/beans/factory/annotation/AutowiredAnnotationBeanPostProcessor.java

1 public void postProcessMergedBeanDefinition(RootBeanDefinition beanDefinition, Class<?> beanType, String beanName) {
2         InjectionMetadata metadata = findAutowiringMetadata(beanName, beanType, null);
3         metadata.checkConfigMembers(beanDefinition);
4     }

第四次執行后置處理器：

　　代碼路徑：org/springframework/beans/factory/support/AbstractAutowireCapableBeanFactory.java

　　　　　　　　AbstractAutowireCapableBeanFactory.getEarlyBeanReference()---第四次執行后置處理器

 1 protected Object getEarlyBeanReference(String beanName, RootBeanDefinition mbd, Object bean) {
 2         Object exposedObject = bean;
 3         if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
 4             for (BeanPostProcessor bp : getBeanPostProcessors()) {
 5                 if (bp instanceof SmartInstantiationAwareBeanPostProcessor) {
 6                     SmartInstantiationAwareBeanPostProcessor ibp = (SmartInstantiationAwareBeanPostProcessor) bp;
 7                     exposedObject = ibp.getEarlyBeanReference(exposedObject, beanName);
 8                 }
 9             }
10         }
11         return exposedObject;
12     }

　　SmartInstantiationAwareBeanPostProcessor.getEarlyBeanReference()//解決循環依賴的

1 @Override
2     public Object getEarlyBeanReference(Object bean, String beanName) throws BeansException {
3         return bean;
4     }

第五次執行后置處理器：

　　代碼路徑：

org/springframework/beans/factory/support/AbstractAutowireCapableBeanFactory.java
AbstractAutowireCapableBeanFactory.populateBean()--InstantiationAwareBeanPostProcessor.postProcessAfterInstantiation()---第五次執行后置處理器

 1 protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
 2         if (bw == null) {
 3             if (mbd.hasPropertyValues()) {
 4                 throw new BeanCreationException(
 5                         mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance");
 6             }
 7             else {
 8                 // Skip property population phase for null instance.
 9                 return;
10             }
11         }
12 
13         // Give any InstantiationAwareBeanPostProcessors the opportunity to modify the
14         // state of the bean before properties are set. This can be used, for example,
15         // to support styles of field injection.
16         boolean continueWithPropertyPopulation = true;
17         // ***第五次執行后置處理器***
18         if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
19             for (BeanPostProcessor bp : getBeanPostProcessors()) {
20                 if (bp instanceof InstantiationAwareBeanPostProcessor) {
21                     InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
22                     if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
23                         continueWithPropertyPopulation = false;
24                         break;
25                     }
26                 }
27             }
28         }
29 
30         if (!continueWithPropertyPopulation) {
31             return;
32         }
33 
34         PropertyValues pvs = (mbd.hasPropertyValues() ? mbd.getPropertyValues() : null);
35 
36         if (mbd.getResolvedAutowireMode() == AUTOWIRE_BY_NAME || mbd.getResolvedAutowireMode() == AUTOWIRE_BY_TYPE) {
37             MutablePropertyValues newPvs = new MutablePropertyValues(pvs);
38             // Add property values based on autowire by name if applicable.
39             if (mbd.getResolvedAutowireMode() == AUTOWIRE_BY_NAME) {
40                 autowireByName(beanName, mbd, bw, newPvs);
41             }
42             // Add property values based on autowire by type if applicable.
43             if (mbd.getResolvedAutowireMode() == AUTOWIRE_BY_TYPE) {
44                 autowireByType(beanName, mbd, bw, newPvs);
45             }
46             pvs = newPvs;
47         }
48 
49         boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
50         boolean needsDepCheck = (mbd.getDependencyCheck() != AbstractBeanDefinition.DEPENDENCY_CHECK_NONE);
51 
52         PropertyDescriptor[] filteredPds = null;
53         if (hasInstAwareBpps) {
54             if (pvs == null) {
55                 pvs = mbd.getPropertyValues();
56             }
57             for (BeanPostProcessor bp : getBeanPostProcessors()) {
58                 if (bp instanceof InstantiationAwareBeanPostProcessor) {
59                     InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
60                     //
61                     PropertyValues pvsToUse = ibp.postProcessProperties(pvs, bw.getWrappedInstance(), beanName);
62                     if (pvsToUse == null) {
63                         if (filteredPds == null) {
64                             filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
65                         }
66                         // ***第六次執行后置處理器***
67                         pvsToUse = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
68                         if (pvsToUse == null) {
69                             return;
70                         }
71                     }
72                     pvs = pvsToUse;
73                 }
74             }
75         }
76         if (needsDepCheck) {
77             if (filteredPds == null) {
78                 filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
79             }
80             checkDependencies(beanName, mbd, filteredPds, pvs);
81         }
82 
83         if (pvs != null) {
84             applyPropertyValues(beanName, mbd, bw, pvs);
85         }
86     }

InstantiationAwareBeanPostProcessor.postProcessAfterInstantiation();

1 @Override
2     public boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {
3         return true;
4     }

第六次執行后置處理器：

　　代碼路徑：org/springframework/beans/factory/support/AbstractAutowireCapableBeanFactory.java

　　　　AbstractAutowireCapableBeanFactory.populateBean()--InstantiationAwareBeanPostProcessor.postProcessPropertyValues()---第六次執行后置處理器

populateBean（）//同上面第五次調用后置處理器

　　InstantiationAwareBeanPostProcessor.postProcessPropertyValues();

1 public PropertyValues postProcessPropertyValues(
2             PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) {
3 
4         return postProcessProperties(pvs, bean, beanName);
5     }

第七次執行后置處理器：

　　代碼路徑：org/springframework/beans/factory/support/AbstractAutowireCapableBeanFactory.java

　　　　AbstractAutowireCapableBeanFactory.initializeBean()--applyBeanPostProcessorsBeforeInitialization()--BeanPostProcessor.postProcessBeforeInitialization()---第七次執行后置處理器

 1 protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) {
 2         if (System.getSecurityManager() != null) {
 3             AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
 4                 invokeAwareMethods(beanName, bean);
 5                 return null;
 6             }, getAccessControlContext());
 7         }
 8         else {
 9             invokeAwareMethods(beanName, bean);
10         }
11 
12         Object wrappedBean = bean;
13         if (mbd == null || !mbd.isSynthetic()) {
14             //***第七次調用后置處理器***
15             wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
16         }
17 
18         try {
19             invokeInitMethods(beanName, wrappedBean, mbd);
20         }
21         catch (Throwable ex) {
22             throw new BeanCreationException(
23                     (mbd != null ? mbd.getResourceDescription() : null),
24                     beanName, "Invocation of init method failed", ex);
25         }
26         if (mbd == null || !mbd.isSynthetic()) {
27             //***第八次調用后置處理器***
28             wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
29         }
30 
31         return wrappedBean;
32     }

 1 public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
 2             throws BeansException {
 3 
 4         Object result = existingBean;
 5         for (BeanPostProcessor processor : getBeanPostProcessors()) {
 6             Object current = processor.postProcessBeforeInitialization(result, beanName);
 7             if (current == null) {
 8                 return result;
 9             }
10             result = current;
11         }
12         return result;
13     }

第八次執行后置處理器：

　　代碼路徑：org/springframework/beans/factory/support/AbstractAutowireCapableBeanFactory.java

　　　　　　AbstractAutowireCapableBeanFactory.initializeBean()--applyBeanPostProcessorsAfterInitialization()--BeanPostProcessor.postProcessAfterInitialization()---第八次執行后置處理器

 1 public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
 2             throws BeansException {
 3 
 4         Object result = existingBean;
 5         for (BeanPostProcessor processor : getBeanPostProcessors()) {
 6             Object current = processor.postProcessAfterInitialization(result, beanName);
 7             if (current == null) {
 8                 return result;
 9             }
10             result = current;
11         }
12         return result;
13     }

第九次執行后置處理器：

　　bean銷毀的時候執行的后置處理器。

Spring執行BeanPostProcessor的時間和作用：

　　當一個bean實例化的過程中，首先會初始化bean的構造方法，然后執行BeanPostProcessor.postProcessBeforeInitialization()方法，然后執行添加@PostConstruct注解的方法，然后執行BeanPostProcessor.postProcessAfterInitialization()的方法。（spring-aop的實行原理）

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