spring代码片段赏析

//---------------------------------------------------------------------
// Abstract methods to be implemented by subclasses
//---------------------------------------------------------------------

    /**
     * Check if this bean factory contains a bean definition with the given name.
     * Does not consider any hierarchy this factory may participate in.
     * Invoked by {@code containsBean} when no cached singleton instance is found.
     * <p>Depending on the nature of the concrete bean factory implementation,
     * this operation might be expensive (for example, because of directory lookups
     * in external registries). However, for listable bean factories, this usually
     * just amounts to a local hash lookup: The operation is therefore part of the
     * public interface there. The same implementation can serve for both this
     * template method and the public interface method in that case.
     * @param beanName the name of the bean to look for
     * @return if this bean factory contains a bean definition with the given name
     * @see #containsBean
     * @see org.springframework.beans.factory.ListableBeanFactory#containsBeanDefinition
     */
    protected abstract boolean containsBeanDefinition(String beanName);

    /**
     * Return the bean definition for the given bean name.
     * Subclasses should normally implement caching, as this method is invoked
     * by this class every time bean definition metadata is needed.
     * <p>Depending on the nature of the concrete bean factory implementation,
     * this operation might be expensive (for example, because of directory lookups
     * in external registries). However, for listable bean factories, this usually
     * just amounts to a local hash lookup: The operation is therefore part of the
     * public interface there. The same implementation can serve for both this
     * template method and the public interface method in that case.
     * @param beanName the name of the bean to find a definition for
     * @return the BeanDefinition for this prototype name (never {@code null})
     * @throws org.springframework.beans.factory.NoSuchBeanDefinitionException
     * if the bean definition cannot be resolved
     * @throws BeansException in case of errors
     * @see RootBeanDefinition
     * @see ChildBeanDefinition
     * @see org.springframework.beans.factory.config.ConfigurableListableBeanFactory#getBeanDefinition
     */
    protected abstract BeanDefinition getBeanDefinition(String beanName) throws BeansException;

    /**
     * Create a bean instance for the given merged bean definition (and arguments).
     * The bean definition will already have been merged with the parent definition
     * in case of a child definition.
     * <p>All bean retrieval methods delegate to this method for actual bean creation.
     * @param beanName the name of the bean
     * @param mbd the merged bean definition for the bean
     * @param args explicit arguments to use for constructor or factory method invocation
     * @return a new instance of the bean
     * @throws BeanCreationException if the bean could not be created
     */
    protected abstract Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
            throws BeanCreationException;

enter image description here

如图所示为AbstractBeanFactory类的模板方法，在模板方法前可加具体注释说明，而且每个模板方法需详细说明