2-3.spring源码--BeanFactoryPostProcessor

Spring源码–BeanFactoryPostProcessor

对于BeanFactoryPostProcessor下面是官方api文档给出的定义：

连接工厂允许修改自定义应用的bean信息，可以调整底层bean工厂的属性值。（Factory hook that allows for custom modification of an application context's bean definitions, adapting the bean property values of the context's underlying bean factory.）
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从上面 的文档上看就是可以修改bean信息，但是修改的触发节点是在bean实例化前才会有效果 。看下BeanFactoryPostProcessor的源码：

public interface BeanFactoryPostProcessor {
	void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException;

}
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从源码中可以看出，这个接口只有一个接口，所有的实现都是集成这个接口，下面 是实现接口的对应类型。

下面看下这个其中一个的源码：

		public BeanFactoryPostProcessor beanFactoryPostProcessor() {
			return new BeanFactoryPostProcessor() {
				@Override
				public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
					BeanDefinition bd = beanFactory.getBeanDefinition("beanPostProcessor");
					bd.getPropertyValues().addPropertyValue("nameSuffix", "-processed-" + myProp);
				}
			};
		}
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以上核心代码只有两个句，第一步：BeanDefinition bd = beanFactory.getBeanDefinition(“beanPostProcessor”);通过bean工厂 获取到BeanDefinition的对象。第二步：bd.getPropertyValues().addPropertyValue(“nameSuffix”, “-processed-” + myProp);对于bean加入 属性。

下面我们举个栗子，看下BeanFactoryPostProcessor使用情况：

集成BeanFactoryPostProcessor接口，实现重写postProcessBeanFactory方法：

public class NameBeanFactoryPostProcessor implements BeanFactoryPostProcessor {
	@Override
	public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
		System.out.println("-->NameBeanFactoryPostProcessor start");
		String[] names = beanFactory.getBeanDefinitionNames();
		for (String name : names) {
			if("a".equals(name)){

				BeanDefinition beanDefinition = beanFactory.getBeanDefinition(name);
				MutablePropertyValues propertyValues = beanDefinition.getPropertyValues();
				if(propertyValues.contains("name")){
					propertyValues.addPropertyValue("name", "王五");
					System.out.println("-->mod bean definition name");
				}
			}
		}
		System.out.println("-->NameBeanFactoryPostProcessor  end");
	}
}
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执行触发方法：

public class TestAB {
	public static void main(String[] args) {
		ApplicationContext applicationContext= new ClassPathXmlApplicationContext("x.xml");
		A a=applicationContext.getBean(A.class);
		System.out.println("-->NameBeanFactoryPostProcessor test end!");
		System.out.println("-->name :"+ a.getName());
	}
}
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看下A类的xml的文件内容：

	
		
	
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执行结果：

-->NameBeanFactoryPostProcessor start
-->mod bean definition name
-->NameBeanFactoryPostProcessor  end
-->BeanFactoryPostProcessor test end!
-->name :王五
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A类的属性被修改了 , 从张三 -> 王五。

下面思考一个问题，如果有多个BeanFactoryPostProcessor存在怎么办？

这时候给A类加一个age属性，再添加AgeBeanFactoryPostProcessor，这时有两个BeanFactoryPostProcessor，这时就用到了我们之前降到的AbstractApplicationContext实现类中的refresh方法，在refresh方法中有进行，回顾一下refresh方法与beanFactory相关的四个方法：

			//创建
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
			//准备	
			prepareBeanFactory(beanFactory);
			//空方法
			postProcessBeanFactory(beanFactory);
			//处理逻辑
			invokeBeanFactoryPostProcessors(beanFactory);
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进入invokeBeanFactoryPostProcessors(beanFactory)展示源码：

	protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
		//逻辑处理
		PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());
		//后续处理
		if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
			beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
			beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
		}
	}
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在进入PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());方法中，查看源码

	public static void invokeBeanFactoryPostProcessors(
			ConfigurableListableBeanFactory beanFactory, List beanFactoryPostProcessors) {
			
		//......省略了部分代码，代码太长了，了解这块内容看这里就行了

		// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
		//首先，调用实现 PriorityOrdered 的 BeanFactoryPostProcessor。
		sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
		invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

		// Next, invoke the BeanFactoryPostProcessors that implement Ordered.
		//接下来，调用实现 Ordered 的 BeanFactoryPostProcessors。
		List orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
		for (String postProcessorName : orderedPostProcessorNames) {
			orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
		}
		sortPostProcessors(orderedPostProcessors, beanFactory);
		invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);

		// Finally, invoke all other BeanFactoryPostProcessors.
		//最后，调用所有其他 BeanFactoryPostProcessor。
		List nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size());
		for (String postProcessorName : nonOrderedPostProcessorNames) {
			nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
		}
		invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
	}
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在上面源码中可以看出，在执行优先级 实现PriorityOrdered > 实现Ordered > 其他 。所以PriorityOrdered 和Ordered 是影响BeanFactoryPostProcessors执行顺序的最终因素。下面看下PriorityOrdered 和Ordered 源码：

public interface PriorityOrdered extends Ordered {
}

public interface Ordered {

	int HIGHEST_PRECEDENCE = Integer.MIN_VALUE;

	int LOWEST_PRECEDENCE = Integer.MAX_VALUE;

	/**
	 * Get the order value of this object.
	 * 
Higher values are interpreted as lower priority. As a consequence,
	 * the object with the lowest value has the highest priority (somewhat
	 * analogous to Servlet {@code load-on-startup} values).
	 * 
Same order values will result in arbitrary sort positions for the
	 * affected objects.
	 * @return the order value
	 * @see #HIGHEST_PRECEDENCE
	 * @see #LOWEST_PRECEDENCE
	 */
	int getOrder();

}
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从源码上可以看出来PriorityOrdered是继承了Ordered接口，所以下面我们以Ordered接口为例，去验证多个BeanFactoryPostProcessors类。

NameBeanFactoryPostProcessor类

public class NameBeanFactoryPostProcessor implements BeanFactoryPostProcessor, Ordered {
	@Override
	public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
		System.out.println("-->NameBeanFactoryPostProcessor start");
		String[] names = beanFactory.getBeanDefinitionNames();
		for (String name : names) {
			if("a".equals(name)){

				BeanDefinition beanDefinition = beanFactory.getBeanDefinition(name);
				MutablePropertyValues propertyValues = beanDefinition.getPropertyValues();
				if(propertyValues.contains("name")){
					propertyValues.addPropertyValue("name", "王五");
					System.out.println("-->mod bean definition name");
				}
			}
		}
		System.out.println("-->NameBeanFactoryPostProcessor  end");
	}

	@Override
	public int getOrder() {
		return 1;
	}
}


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AgeBeanFactoryPostProcessor类

public class AgeBeanFactoryPostProcessor implements BeanFactoryPostProcessor, Ordered {
	@Override
	public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
		System.out.println("-->AgeBeanFactoryPostProcessor start");
		String[] names = beanFactory.getBeanDefinitionNames();
		for (String name : names) {
			if("a".equals(name)){

				BeanDefinition beanDefinition = beanFactory.getBeanDefinition(name);
				MutablePropertyValues propertyValues = beanDefinition.getPropertyValues();
				if(propertyValues.contains("name")){
					propertyValues.addPropertyValue("age", 12);
					System.out.println("-->mod bean definition age");
				}
			}
		}
		System.out.println("-->AgeBeanFactoryPostProcessor  end");
	}

	@Override
	public int getOrder() {
		return 2;
	}
}

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x.xml文件

	
		
		
	
	
	
	
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启动方法

	public static void main(String[] args) {
		ApplicationContext applicationContext= new ClassPathXmlApplicationContext("x.xml");
		A a=applicationContext.getBean(A.class);
		System.out.println("-->BeanFactoryPostProcessor test end!");
		System.out.println("-->name :"+ a.getName());
		System.out.println("-->age :"+ a.getAge());
	}
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执行结果

-->NameBeanFactoryPostProcessor start
-->mod bean definition name
-->NameBeanFactoryPostProcessor  end
-->AgeBeanFactoryPostProcessor start
-->mod bean definition age
-->AgeBeanFactoryPostProcessor  end
-->BeanFactoryPostProcessor test end!
-->name :王五
-->age :12
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从输出结果上看确实是先执行的NameBeanFactoryPostProcessor，后置执行的AgeBeanFactoryPostProcessor，与设置的order数字是一致的。

坚持吧！！！ 坚持卷spring源码