5.5准备创建bean

AbstractAutowireCapableBeanFactory
protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
    throws BeanCreationException {

    if (logger.isTraceEnabled()) {
        logger.trace("Creating instance of bean '" + beanName + "'");
    }
    RootBeanDefinition mbdToUse = mbd;

    // Make sure bean class is actually resolved at this point, and
    // clone the bean definition in case of a dynamically resolved Class
    // which cannot be stored in the shared merged bean definition.
    //锁定class，根据设定的class属性或者根据className来解析Class
    Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
    if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
        mbdToUse = new RootBeanDefinition(mbd);
        mbdToUse.setBeanClass(resolvedClass);
    }

    // Prepare method overrides.
    //验证及准备覆盖方法
    try {
        mbdToUse.prepareMethodOverrides();
    }
    catch (BeanDefinitionValidationException ex) {
        throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(),
                                               beanName, "Validation of method overrides failed", ex);
    }

    try {
        // Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
        //给BeanPostProcessors一个机会来返回一个代理用来来替代真正的实例（AOP？）
        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);
    }

    try {
        Object beanInstance = doCreateBean(beanName, mbdToUse, args);
        if (logger.isTraceEnabled()) {
            logger.trace("Finished creating instance of bean '" + beanName + "'");
        }
        return beanInstance;
    }
    catch (BeanCreationException | ImplicitlyAppearedSingletonException ex) {
        // A previously detected exception with proper bean creation context already,
        // or illegal singleton state to be communicated up to DefaultSingletonBeanRegistry.
        throw ex;
    }
    catch (Throwable ex) {
        throw new BeanCreationException(
            mbdToUse.getResourceDescription(), beanName, "Unexpected exception during bean creation", ex);
    }
}

大致逻辑：

1）根据设置的class属性或者根据className来解析Class。

2）对override属性进行标记及验证（lookup-method、replace-method，统一存放在BeanDefinition的methodOverrides属性）。

3）应用初始化前的后处理。解析指定bean是否存放在初始化前的短路操作。

4）创建bean。

 

5.5.1处理override属性

public void prepareMethodOverrides() throws BeanDefinitionValidationException {
    // Check that lookup methods exist and determine their overloaded status.
    if (hasMethodOverrides()) {
        getMethodOverrides().getOverrides().forEach(this::prepareMethodOverride);
    }
}

protected void prepareMethodOverride(MethodOverride mo) throws BeanDefinitionValidationException {
    //获取对应类中对应方法名的个数
    int count = ClassUtils.getMethodCountForName(getBeanClass(), mo.getMethodName());
    if (count == 0) {
        throw new BeanDefinitionValidationException(
            "Invalid method override: no method with name '" + mo.getMethodName() +
            "' on class [" + getBeanClassName() + "]");
    }
    else if (count == 1) {
        // Mark override as not overloaded, to avoid the overhead of arg type checking.
        //标记MethodOverride暂未被覆盖，避免参数类型检查的开销
        mo.setOverloaded(false);
    }
}

这两个功能实现原理其实是bean实例化的时候如果检测到存在MethodOverride属性，会动态为当前bean生成代理并使用对应的拦截器为bean做增强处理。相关逻辑实现在bean的实例化部分详细介绍。

 

5.5.2实例化的前置处理

//TODO 这一块不太明白

来自为知笔记(Wiz)