SpringBoot注解扩展篇(2)-BeanFactory的前置处理

继续接着讲prepareBeanFactory()的流程,这一步的主要作用是BeanFactory的预准备工作,也就是对BeanFactory进行一些初始化后的设置;

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进入这个方法的实现之前,我们来看下方法上面的注释,Configure the factory's standard context characteristics, such as the context's ClassLoader and post-processors.翻译后的大概意思就是:设置这个BeanFactory的标准上下文特性,比如比如上下文的类加载器和后置处理器。传进来的参数是待配置的beanFactory。ok,看下其源码:

protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
    beanFactory.setBeanClassLoader(getClassLoader());
        beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
        beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));
        beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);       beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
beanFactory.registerResolvableDependency(ResourceLoader.class, this);
beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
beanFactory.registerResolvableDependency(ApplicationContext.class, this);
        beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));

        if (beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
            beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
        
            beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
        }

        
        if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
            beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
        }
        if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
            beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
        }
        if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
            beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
        }
    }

首先:
1.设置BeanFactory的BeanClassLoader,如果存在,则直接使用之前的那个,否则,初始化一个新的ClassLoader;
2.设置BeanExpressionResolver表达式解析器,主要用来解析EL表达式;那么什么时候会进行EL表达式的解析嘞?可以提前剧透下,也就是在Bean进行初始化后会有属性填充的一步,方法如下:

protected void populateBean(String beanName, RootBeanDefinition mbd, BeanWrapper bw) {

...

//属性填充
applyPropertyValues(beanName, mbd, bw, pvs);
}

在这一步中会调用BeanDefinitionValueResolver valueResolver = new BeanDefinitionValueResolver(this, beanName, mbd, converter); 来进行属性值的解析;而接下来便是通过AbstractBeanFactory中的evaluateBeanDefinitionString方法进行解析,解析代码如下:

protected Object evaluateBeanDefinitionString(String value, BeanDefinition beanDefinition) {
        if (this.beanExpressionResolver == null) {
            return value;
        }
        Scope scope = (beanDefinition != null ? getRegisteredScope(beanDefinition.getScope()) : null);
        return this.beanExpressionResolver.evaluate(value, new BeanExpressionContext(this, scope));
    }

然后这时候就进到StandardBeanExpressionResolver中的evaluate方法中进行解析了;

3.设置属性注册解析器PropertyEditor;这个主要是对某些注入的Bean的一些属性的支持;
4.设置ApplicationContextAwareProcessor的支持,关于BeanPostProcessor的作用我这里不在赘述,在这个地方仅仅是注册,真是的实现还是在ApplicationContextAwareProcessor的内部,先看其前置处理.

public Object postProcessBeforeInitialization(final Object bean, String beanName) throws BeansException {
        AccessControlContext acc = null;

        if (System.getSecurityManager() != null &&
                (bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware ||
                        bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware ||
                        bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware)) {
            acc = this.applicationContext.getBeanFactory().getAccessControlContext();
        }

        if (acc != null) {
            AccessController.doPrivileged(new PrivilegedAction