Spring的BeanFactoryPostProcessor和BeanPostProcessor

轉載：http://blog.csdn.net/caihaijiang/article/details/35552859

BeanFactoryPostProcessor和BeanPostProcessor，這兩個接口，都是spring初始化bean時對外暴露的擴展點。兩個接口名稱看起來很相似，但作用及使用場景卻不同，分析如下：

1、BeanFactoryPostProcessor接口

該接口的定義如下：

public interface BeanFactoryPostProcessor {

    /**
     * Modify the application context's internal bean factory after its standard
     * initialization. All bean definitions will have been loaded, but no beans
     * will have been instantiated yet. This allows for overriding or adding
     * properties even to eager-initializing beans.
     * @param beanFactory the bean factory used by the application context
     * @throws org.springframework.beans.BeansException in case of errors
     */
    void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException;

}

實現該接口，可以在spring的bean創建之前，修改bean的定義屬性。也就是說，Spring允許BeanFactoryPostProcessor在容器實例化任何其它bean之前讀取配置元數據，並可以根據需要進行修改，例如可以把bean的scope從singleton改爲prototype，也可以把property的值給修改掉。可以同時配置多個BeanFactoryPostProcessor，並通過設置'order'屬性來控制各個BeanFactoryPostProcessor的執行次序。
注意：BeanFactoryPostProcessor是在spring容器加載了bean的定義文件之後，在bean實例化之前執行的。接口方法的入參是ConfigurrableListableBeanFactory，使用該參數，可以獲取到相關bean的定義信息，例子：

1）spring bean的定義：

<?xml version="1.0" encoding="UTF-8" ?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
    xmlns:p="http://www.springframework.org/schema/p" xmlns:tx="http://www.springframework.org/schema/tx"
    xmlns:aop="http://www.springframework.org/schema/aop"
    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
                http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd
                http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd"
    default-autowire="byName">

    <bean id="myJavaBean" class="com.ali.caihj.postprocessor.MyJavaBean">
        <property name="desc" value="測試一下啦" />
        <property name="remark" value="這是備註信息啦啦啦" />
    </bean>
    <bean id="myBeanFactoryPostProcessor" class="com.ali.caihj.postprocessor.MyBeanFactoryPostProcessor" />
</beans>

2）自定義的BeanFactoryPostProcessor：

public class MyBeanFactoryPostProcessor implements BeanFactoryPostProcessor {

    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        System.out.println("調用MyBeanFactoryPostProcessor的postProcessBeanFactory");
        BeanDefinition bd = beanFactory.getBeanDefinition("myJavaBean");
        System.out.println("屬性值============" + bd.getPropertyValues().toString());
        MutablePropertyValues pv =  bd.getPropertyValues();
        if (pv.contains("remark")) {
            pv.addPropertyValue("remark", "把備註信息修改一下");
        }
        bd.setScope(BeanDefinition.SCOPE_PROTOTYPE);
    }

}

spring中，有內置的一些BeanFactoryPostProcessor實現類，常用的有：

• org.springframework.beans.factory.config.PropertyPlaceholderConfigurer
• org.springframework.beans.factory.config.PropertyOverrideConfigurer
• org.springframework.beans.factory.config.CustomEditorConfigurer：用來註冊自定義的屬性編輯器
  

2、BeanPostProcessor接口

該接口的定義如下：

public interface BeanPostProcessor {

    /**
     * Apply this BeanPostProcessor to the given new bean instance <i>before</i> any bean
     * initialization callbacks (like InitializingBean's <code>afterPropertiesSet</code>
     * or a custom init-method). The bean will already be populated with property values.
     * The returned bean instance may be a wrapper around the original.
     * @param bean the new bean instance
     * @param beanName the name of the bean
     * @return the bean instance to use, either the original or a wrapped one
     * @throws org.springframework.beans.BeansException in case of errors
     * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
     */
    Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException;

    /**
     * Apply this BeanPostProcessor to the given new bean instance <i>after</i> any bean
     * initialization callbacks (like InitializingBean's <code>afterPropertiesSet</code>
     * or a custom init-method). The bean will already be populated with property values.
     * The returned bean instance may be a wrapper around the original.
     * <p>In case of a FactoryBean, this callback will be invoked for both the FactoryBean
     * instance and the objects created by the FactoryBean (as of Spring 2.0). The
     * post-processor can decide whether to apply to either the FactoryBean or created
     * objects or both through corresponding <code>bean instanceof FactoryBean</code> checks.
     * <p>This callback will also be invoked after a short-circuiting triggered by a
     * {@link InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation} method,
     * in contrast to all other BeanPostProcessor callbacks.
     * @param bean the new bean instance
     * @param beanName the name of the bean
     * @return the bean instance to use, either the original or a wrapped one
     * @throws org.springframework.beans.BeansException in case of errors
     * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
     * @see org.springframework.beans.factory.FactoryBean
     */
    Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException;

}

BeanPostProcessor，可以在spring容器實例化bean之後，在執行bean的初始化方法前後，添加一些自己的處理邏輯。這裏說的初始化方法，指的是下面兩種：

1）bean實現了InitializingBean接口，對應的方法爲afterPropertiesSet

2）在bean定義的時候，通過init-method設置的方法

注意：BeanPostProcessor是在spring容器加載了bean的定義文件並且實例化bean之後執行的。BeanPostProcessor的執行順序是在BeanFactoryPostProcessor之後。

spring中，有內置的一些BeanPostProcessor實現類，例如：

• org.springframework.context.annotation.CommonAnnotationBeanPostProcessor：支持@Resource註解的注入
• org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor：支持@Required註解的注入
• org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor：支持@Autowired註解的注入
• org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor：支持@PersistenceUnit和@PersistenceContext註解的注入
• org.springframework.context.support.ApplicationContextAwareProcessor：用來爲bean注入ApplicationContext等容器對象
  

這些註解類的BeanPostProcessor，在spring配置文件中，可以通過這樣的配置 <context:component-scan base-package="*.*" /> ，自動進行註冊。（spring通過ComponentScanBeanDefinitionParser類來解析該標籤）

3、下面通過完整的一個例子，來加深理解

1）定義一個JavaBean

public class MyJavaBean implements InitializingBean {
    private String desc;
    private String remark;

    public MyJavaBean() {
        System.out.println("MyJavaBean的構造函數被執行啦");
    }
    public String getDesc() {
        return desc;
    }
    public void setDesc(String desc) {
        System.out.println("調用setDesc方法");
        this.desc = desc;
    }
    public String getRemark() {
        return remark;
    }
    public void setRemark(String remark) {
        System.out.println("調用setRemark方法");
        this.remark = remark;
    }
    public void afterPropertiesSet() throws Exception {
        System.out.println("調用afterPropertiesSet方法");
        this.desc = "在初始化方法中修改之後的描述信息";
    }
    public void initMethod() {
        System.out.println("調用initMethod方法");
    }
    public String toString() {
        StringBuilder builder = new StringBuilder();
        builder.append("[描述：").append(desc);
        builder.append("， 備註：").append(remark).append("]");
        return builder.toString();
    }
}

2）定義一個BeanFactoryPostProcessor

public class MyBeanFactoryPostProcessor implements BeanFactoryPostProcessor {

    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        System.out.println("調用MyBeanFactoryPostProcessor的postProcessBeanFactory");
        BeanDefinition bd = beanFactory.getBeanDefinition("myJavaBean");
        MutablePropertyValues pv =  bd.getPropertyValues();
        if (pv.contains("remark")) {
            pv.addPropertyValue("remark", "在BeanFactoryPostProcessor中修改之後的備忘信息");
        }
    }

}

3）定義一個BeanPostProcessor

public class MyBeanPostProcessor implements BeanPostProcessor {

    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("BeanPostProcessor，對象" + beanName + "調用初始化方法之前的數據： " + bean.toString());
        return bean;
    }
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("BeanPostProcessor，對象" + beanName + "調用初始化方法之後的數據：" + bean.toString());
        return bean;
    }
}

4）spring的配置

<?xml version="1.0" encoding="UTF-8" ?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
    xmlns:p="http://www.springframework.org/schema/p" xmlns:tx="http://www.springframework.org/schema/tx"
    xmlns:aop="http://www.springframework.org/schema/aop"
    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
                http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd
                http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd"
    default-autowire="byName">

    <bean id="myJavaBean" class="com.ali.caihj.postprocessor.MyJavaBean" init-method="initMethod">
        <property name="desc" value="原始的描述信息" />
        <property name="remark" value="原始的備註信息" />
    </bean>

    <bean id="myBeanPostProcessor" class="com.ali.caihj.postprocessor.MyBeanPostProcessor" />
    <bean id="myBeanFactoryPostProcessor" class="com.ali.caihj.postprocessor.MyBeanFactoryPostProcessor" />
</beans>

5）測試類

public class PostProcessorMain {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("config/postprocessor.xml");
        MyJavaBean bean = (MyJavaBean) context.getBean("myJavaBean");
        System.out.println("===============下面輸出結果============");
        System.out.println("描述：" + bean.getDesc());
        System.out.println("備註：" + bean.getRemark());

    }
}

6）運行結果如下：

7）分析

從上面的結果可以看出，BeanFactoryPostProcessor在bean實例化之前執行，之後實例化bean（調用構造函數，並調用set方法注入屬性值），然後在調用兩個初始化方法前後，執行了BeanPostProcessor。初始化方法的執行順序是，先執行afterPropertiesSet，再執行init-method。

4、進一步深入分析

在使用ApplicationContext啓動spring容器的時候，在AbstractApplicationContext.refresh()方法中，完成相關初始化工作：

1）BeanFactoryPostProcessor.postProcessBeanFactory，是在第5步執行的，invokeBeanFactoryPostProcessors方法實現如下：

/**
     * Instantiate and invoke all registered BeanFactoryPostProcessor beans,
     * respecting explicit order if given.
     * <p>Must be called before singleton instantiation.
     */
    protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
        // Invoke factory processors registered with the context instance.
        for (Iterator it = getBeanFactoryPostProcessors().iterator(); it.hasNext();) {
            BeanFactoryPostProcessor factoryProcessor = (BeanFactoryPostProcessor) it.next();
            factoryProcessor.postProcessBeanFactory(beanFactory);
        }

        // Do not initialize FactoryBeans here: We need to leave all regular beans
        // uninitialized to let the bean factory post-processors apply to them!
        String[] postProcessorNames =
                beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);

        // Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
        // Ordered, and the rest.
        List priorityOrderedPostProcessors = new ArrayList();
        List orderedPostProcessorNames = new ArrayList();
        List nonOrderedPostProcessorNames = new ArrayList();
        for (int i = 0; i < postProcessorNames.length; i++) {
            if (isTypeMatch(postProcessorNames[i], PriorityOrdered.class)) {
                priorityOrderedPostProcessors.add(beanFactory.getBean(postProcessorNames[i]));
            }
            else if (isTypeMatch(postProcessorNames[i], Ordered.class)) {
                orderedPostProcessorNames.add(postProcessorNames[i]);
            }
            else {
                nonOrderedPostProcessorNames.add(postProcessorNames[i]);
            }
        }

        // First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
        Collections.sort(priorityOrderedPostProcessors, new OrderComparator());
        invokeBeanFactoryPostProcessors(beanFactory, priorityOrderedPostProcessors);

        // Next, invoke the BeanFactoryPostProcessors that implement Ordered.
        List orderedPostProcessors = new ArrayList();
        for (Iterator it = orderedPostProcessorNames.iterator(); it.hasNext();) {
            String postProcessorName = (String) it.next();
            orderedPostProcessors.add(getBean(postProcessorName));
        }
        Collections.sort(orderedPostProcessors, new OrderComparator());
        invokeBeanFactoryPostProcessors(beanFactory, orderedPostProcessors);

        // Finally, invoke all other BeanFactoryPostProcessors.
        List nonOrderedPostProcessors = new ArrayList();
        for (Iterator it = nonOrderedPostProcessorNames.iterator(); it.hasNext();) {
            String postProcessorName = (String) it.next();
            nonOrderedPostProcessors.add(getBean(postProcessorName));
        }
        invokeBeanFactoryPostProcessors(beanFactory, nonOrderedPostProcessors);
    }

    /**
     * Invoke the given BeanFactoryPostProcessor beans.
     */
    private void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory, List postProcessors) {
        for (Iterator it = postProcessors.iterator(); it.hasNext();) {
            BeanFactoryPostProcessor postProcessor = (BeanFactoryPostProcessor) it.next();
            postProcessor.postProcessBeanFactory(beanFactory);
        }
    }

通過beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false)，獲取spring配置文件中定義的所有實現BeanFactoryPostProcessor接口的bean，然後根據優先級進行排序，之後對於每個BeanFactoryPostProcessor，調用postProcessBeanFactory方法。

2）而BeanPostProcessor的執行，取決於配置文件中bean的定義，如果定義的bean是singleton並且不是抽象類，也不延遲初始化，則BeanPostProcessor是在第11步中執行；而對於prototype的bean，BeanPostProcessor是在程序getBean的時候執行的。在第6步中，調用registerBeanPostProcessors方法，註冊所有實現BeanPostProcessor接口的bean，該方法的實現如下：

protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
        String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);

        // Register BeanPostProcessorChecker that logs an info message when
        // a bean is created during BeanPostProcessor instantiation, i.e. when
        // a bean is not eligible for getting processed by all BeanPostProcessors.
        int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
        beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));

        // Separate between BeanPostProcessors that implement PriorityOrdered,
        // Ordered, and the rest.
        List priorityOrderedPostProcessors = new ArrayList();
        List orderedPostProcessorNames = new ArrayList();
        List nonOrderedPostProcessorNames = new ArrayList();
        for (int i = 0; i < postProcessorNames.length; i++) {
            if (isTypeMatch(postProcessorNames[i], PriorityOrdered.class)) {
                priorityOrderedPostProcessors.add(beanFactory.getBean(postProcessorNames[i]));
            }
            else if (isTypeMatch(postProcessorNames[i], Ordered.class)) {
                orderedPostProcessorNames.add(postProcessorNames[i]);
            }
            else {
                nonOrderedPostProcessorNames.add(postProcessorNames[i]);
            }
        }

        // First, register the BeanPostProcessors that implement PriorityOrdered.
        Collections.sort(priorityOrderedPostProcessors, new OrderComparator());
        registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);

        // Next, register the BeanPostProcessors that implement Ordered.
        List orderedPostProcessors = new ArrayList();
        for (Iterator it = orderedPostProcessorNames.iterator(); it.hasNext();) {
            String postProcessorName = (String) it.next();
            orderedPostProcessors.add(getBean(postProcessorName));
        }
        Collections.sort(orderedPostProcessors, new OrderComparator());
        registerBeanPostProcessors(beanFactory, orderedPostProcessors);

        // Finally, register all other BeanPostProcessors.
        List nonOrderedPostProcessors = new ArrayList();
        for (Iterator it = nonOrderedPostProcessorNames.iterator(); it.hasNext();) {
            String postProcessorName = (String) it.next();
            nonOrderedPostProcessors.add(getBean(postProcessorName));
        }
        registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);
    }

在第11步中，調用finishBeanFactoryInitialization方法，該方法通過調用DefaultListableBeanFactory.preInstantiateSingletons()，進行相關初始化工作：

從上面的代碼可以看出，對於非抽象類、非延遲初始化的單例bean，在spring容器啓動的時候調用getBean方法來實例化bean，並進行相關初始化工作，getBean方法最終調用AbstractAutowireCapableBeanFactory.doCreateBean方法，該方法的實現如下：

protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args) {
        // Instantiate the bean.
        BeanWrapper instanceWrapper = null;
        if (mbd.isSingleton()) {
            instanceWrapper = (BeanWrapper) this.factoryBeanInstanceCache.remove(beanName);
        }
        if (instanceWrapper == null) {
            instanceWrapper = createBeanInstance(beanName, mbd, args);
        }
        final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
        Class beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null);

        // Allow post-processors to modify the merged bean definition.
        synchronized (mbd.postProcessingLock) {
            if (!mbd.postProcessed) {
                applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
                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.isDebugEnabled()) {
                logger.debug("Eagerly caching bean '" + beanName +
                        "' to allow for resolving potential circular references");
            }
            addSingletonFactory(beanName, new ObjectFactory() {
                public Object getObject() throws BeansException {
                    return getEarlyBeanReference(beanName, mbd, bean);
                }
            });
        }

        // Initialize the bean instance.
        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);
            }
        }

        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 actualDependentBeans = new LinkedHashSet(dependentBeans.length);
                    for (int i = 0; i < dependentBeans.length; i++) {
                        String dependentBean = dependentBeans[i];
                        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 " +
                                "'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.");
                    }
                }
            }
        }

        // Register bean as disposable.
        registerDisposableBeanIfNecessary(beanName, bean, mbd);

        return exposedObject;
    }

在該方法中，首先調用createBeanInstance方法，創建bean實例對象（這個時候執行bean的構造方法），然後調用populateBean方法，對bean進行填充，注入相關依賴，之後再調用方法initializeBean，進行相關初始化工作，initializeBean方法的實現如下：

protected Object initializeBean(String beanName, Object bean, RootBeanDefinition mbd) {
        if (bean instanceof BeanNameAware) {
            ((BeanNameAware) bean).setBeanName(beanName);
        }

        if (bean instanceof BeanClassLoaderAware) {
            ((BeanClassLoaderAware) bean).setBeanClassLoader(getBeanClassLoader());
        }

        if (bean instanceof BeanFactoryAware) {
            ((BeanFactoryAware) bean).setBeanFactory(this);
        }

        Object wrappedBean = bean;
        if (mbd == null || !mbd.isSynthetic()) {
            wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
        }

        try {
            invokeInitMethods(beanName, wrappedBean, mbd);
        }
        catch (Throwable ex) {
            throw new BeanCreationException(
                    (mbd != null ? mbd.getResourceDescription() : null),
                    beanName, "Invocation of init method failed", ex);
        }

        if (mbd == null || !mbd.isSynthetic()) {
            wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
        }
        return wrappedBean;
    }

從上面的實現可以看出，先調用applyBeanPostProcessorsBeforeInitialization方法，執行每個BeanPostProcessor的postProcessBeforeInitialization，然後調用invokeInitMethods方法，執行bean的初始化方法，最後調用applyBeanPostProcessorsAfterInitialization方法，執行每個BeanPostProcessor的postProcessAfterInitialization方法。這三個方法的實現如下：

    public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
            throws BeansException {

        Object result = existingBean;
        for (Iterator it = getBeanPostProcessors().iterator(); it.hasNext();) {
            BeanPostProcessor beanProcessor = (BeanPostProcessor) it.next();
            result = beanProcessor.postProcessBeforeInitialization(result, beanName);
        }
        return result;
    }

    public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
            throws BeansException {

        Object result = existingBean;
        for (Iterator it = getBeanPostProcessors().iterator(); it.hasNext();) {
            BeanPostProcessor beanProcessor = (BeanPostProcessor) it.next();
            result = beanProcessor.postProcessAfterInitialization(result, beanName);
        }
        return result;
    }
protected void invokeInitMethods(String beanName, Object bean, RootBeanDefinition mbd)
            throws Throwable {

        boolean isInitializingBean = (bean instanceof InitializingBean);
        if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod("afterPropertiesSet"))) {
            if (logger.isDebugEnabled()) {
                logger.debug("Invoking afterPropertiesSet() on bean with name '" + beanName + "'");
            }
            ((InitializingBean) bean).afterPropertiesSet();
        }

        String initMethodName = (mbd != null ? mbd.getInitMethodName() : null);
        if (initMethodName != null && !(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&
                !mbd.isExternallyManagedInitMethod(initMethodName)) {
            invokeCustomInitMethod(beanName, bean, initMethodName, mbd.isEnforceInitMethod());
        }
    }

從invokeInitMethods方法的實現可以看出，先執行afterPropertiesSet方法，然後再通過反射，執行init-method指定的方法。

http://jinnianshilongnian.iteye.com/blog/1762632

問題

如下方式可以成功掃描到@Controller註解的Bean，不會掃描@Service/@Repository的Bean。正確

 

 <context:component-scan base-package="org.bdp.system.test.controller">
     <context:include-filter type="annotation" expression="org.springframework.stereotype.Controller"/>
</context:component-scan>

  

但是如下方式，不僅僅掃描@Controller，還掃描@Service/@Repository的Bean，可能造成一些問題

 

 <context:component-scan base-package="org.bdp">
     <context:include-filter type="annotation" expression="org.springframework.stereotype.Controller"/>
</context:component-scan>

 

這個尤其在springmvc+spring+hibernate等集成時最容易出問題的地，最典型的錯誤就是：

事務不起作用

 

這是什麼問題呢？

分析

1、<context:component-scan>會交給org.springframework.context.config.ContextNamespaceHandler處理；

 

registerBeanDefinitionParser("component-scan", new ComponentScanBeanDefinitionParser());

 

2、ComponentScanBeanDefinitionParser會讀取配置文件信息並組裝成org.springframework.context.annotation.ClassPathBeanDefinitionScanner進行處理；

3、如果沒有配置<context:component-scan>的use-default-filters屬性，則默認爲true，在創建ClassPathBeanDefinitionScanner時會根據use-default-filters是否爲true來調用如下代碼：

 

  protected void registerDefaultFilters() {
this.includeFilters.add(new AnnotationTypeFilter(Component.class));
ClassLoader cl = ClassPathScanningCandidateComponentProvider.class.getClassLoader();
try {
    this.includeFilters.add(new AnnotationTypeFilter(
            ((Class<? extends Annotation>) cl.loadClass("javax.annotation.ManagedBean")), false));
    logger.info("JSR-250 'javax.annotation.ManagedBean' found and supported for component scanning");
}
catch (ClassNotFoundException ex) {
    // JSR-250 1.1 API (as included in Java EE 6) not available - simply skip.
}
try {
    this.includeFilters.add(new AnnotationTypeFilter(
            ((Class<? extends Annotation>) cl.loadClass("javax.inject.Named")), false));
    logger.info("JSR-330 'javax.inject.Named' annotation found and supported for component scanning");
}
catch (ClassNotFoundException ex) {
    // JSR-330 API not available - simply skip.
}

 

 

可以看到默認ClassPathBeanDefinitionScanner會自動註冊對@Component、@ManagedBean、@Named註解的Bean進行掃描。如果細心，到此我們就找到問題根源了。

 

 

4、在進行掃描時會通過include-filter/exclude-filter來判斷你的Bean類是否是合法的：

 

protected boolean isCandidateComponent(MetadataReader metadataReader) throws IOException {
    for (TypeFilter tf : this.excludeFilters) {
        if (tf.match(metadataReader, this.metadataReaderFactory)) {
            return false;
        }
    }
    for (TypeFilter tf : this.includeFilters) {
        if (tf.match(metadataReader, this.metadataReaderFactory)) {
            AnnotationMetadata metadata = metadataReader.getAnnotationMetadata();
            if (!metadata.isAnnotated(Profile.class.getName())) {
                return true;
            }
            AnnotationAttributes profile = MetadataUtils.attributesFor(metadata, Profile.class);
            return this.environment.acceptsProfiles(profile.getStringArray("value"));
        }
    }
    return false;
}

 

即

首先通過exclude-filter 進行黑名單過濾；

然後通過include-filter 進行白名單過濾；

否則默認排除。

 

結論

<context:component-scan base-package="org.bdp">
     <context:include-filter type="annotation" expression="org.springframework.stereotype.Controller"/>
</context:component-scan>

 

爲什麼這段代碼不僅僅掃描@Controller註解的Bean，而且還掃描了@Component的子註解@Service、@Reposity。因爲use-default-filters默認爲true。所以如果不需要默認的，則use-default-filters=“false”禁用掉。

 

 

請參考

《SpringMVC + spring3.1.1 + hibernate4.1.0 集成及常見問題總結》 

《第三章 DispatcherServlet詳解 ——跟開濤學SpringMVC》中的ContextLoaderListener初始化的上下文和DispatcherServlet初始化的上下文關係。

Spring源碼解析之初始化 http://blog.csdn.net/pcceo1/article/details/50921162

 

如果在springmvc配置文件，不使用cn.javass.demo.web.controller前綴，而是使用cn.javass.demo，則service、dao層的bean可能也重新加載了，但事務的AOP代理沒有配置在springmvc配置文件中，從而造成新加載的bean覆蓋了老的bean，造成事務失效。只要使用use-default-filters=“false”禁用掉默認的行爲就可以了。