Spring擴展點之BeanFactoryPostProcessor

時間  2019-12-19
標籤 spring 擴展 beanfactorypostprocessor 欄目 Spring 简体版
原文   原文鏈接

前言

BeanFactoryPostProcessor接口是Spring中一個很是重要的接口，它的接口定義以下緩存

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

當你實現了這個接口的時候，能夠對尚未初始化的bean的屬性進行修改或添加app

BeanFactoryPostProcessor註冊

與BeanPostProcessor的統一註冊不一樣，BeanFactoryPostProcessor的註冊是留給具體的業務實現的。它的維護是在AbstractApplicationContext類中post

private final List<BeanFactoryPostProcessor> beanFactoryPostProcessors = 
new ArrayList<>();

	public void addBeanFactoryPostProcessor(BeanFactoryPostProcessor postProcessor) {
		Assert.notNull(postProcessor, "BeanFactoryPostProcessor must not be null");
		this.beanFactoryPostProcessors.add(postProcessor);
	}

執行原理

調用邏輯在AbstractApplicationContext.invokeBeanFactoryPostProcessors方法中 這個方法比較長，能夠重點關注我添加註釋的地方this

protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
		PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());
		if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
			beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
			beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
		}
	}

public static void invokeBeanFactoryPostProcessors(
        ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
 
    Set<String> processedBeans = new HashSet<String>();
 
    // 1.判斷beanFactory是否爲BeanDefinitionRegistry，在這裏普通的beanFactory是DefaultListableBeanFactory,而DefaultListableBeanFactory實現了BeanDefinitionRegistry接口，所以這邊爲true
    if (beanFactory instanceof BeanDefinitionRegistry) {
        BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
        List<BeanFactoryPostProcessor> regularPostProcessors = new LinkedList<BeanFactoryPostProcessor>();
        List<BeanDefinitionRegistryPostProcessor> registryProcessors = new LinkedList<BeanDefinitionRegistryPostProcessor>();
 
        // 2.處理入參beanFactoryPostProcessors
        for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
            if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
                BeanDefinitionRegistryPostProcessor registryProcessor =
                        (BeanDefinitionRegistryPostProcessor) postProcessor;
               // 若是是BeanDefinitionRegistryPostProcessor則直接執行BeanDefinitionRegistryPostProcessor接口的postProcessBeanDefinitionRegistry方法
                registryProcessor.postProcessBeanDefinitionRegistry(registry);
                registryProcessors.add(registryProcessor);
            } else {
                regularPostProcessors.add(postProcessor);
            }
        }
 
        List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<BeanDefinitionRegistryPostProcessor>();
 
        // 3找出全部實現BeanDefinitionRegistryPostProcessor接口的Bean的beanName
        String[] postProcessorNames =
                beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
        for (String ppName : postProcessorNames) {
            // 校驗是否實現了PriorityOrdered接口
            if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                //  獲取對應的bean實例, 添加到currentRegistryProcessors中,
                currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                processedBeans.add(ppName);
            }
        }
        // 排序(根據是否實現PriorityOrdered、Ordered接口和order值來排序)
        sortPostProcessors(currentRegistryProcessors, beanFactory);
        registryProcessors.addAll(currentRegistryProcessors);
        // 遍歷currentRegistryProcessors, 執行postProcessBeanDefinitionRegistry方法
        invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
        // 清空currentRegistryProcessors
        currentRegistryProcessors.clear();
 
        // 4.與上邊3的流程差很少，這是這裏處理的是實現Ordered接口
        postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
        for (String ppName : postProcessorNames) {
            if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
                currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                processedBeans.add(ppName);
            }
        }
        sortPostProcessors(currentRegistryProcessors, beanFactory);
        registryProcessors.addAll(currentRegistryProcessors);
        invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
        currentRegistryProcessors.clear();
 
        // 5.調用全部剩下的BeanDefinitionRegistryPostProcessors
        boolean reiterate = true;
        while (reiterate) {
            reiterate = false;
            // 找出全部實現BeanDefinitionRegistryPostProcessor接口的類
            postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
            for (String ppName : postProcessorNames) {
                // 跳過已經執行過的
                if (!processedBeans.contains(ppName)) {
                    currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                    processedBeans.add(ppName);
                    reiterate = true;
                }
            }
            sortPostProcessors(currentRegistryProcessors, beanFactory);
            registryProcessors.addAll(currentRegistryProcessors);
            // 5遍歷currentRegistryProcessors, 執行postProcessBeanDefinitionRegistry方法
            invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
            currentRegistryProcessors.clear();
        }
 
        // 6.調用全部BeanDefinitionRegistryPostProcessor的postProcessBeanFactory方法
        invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
        // 7.最後, 調用入參beanFactoryPostProcessors中的普通BeanFactoryPostProcessor的postProcessBeanFactory方法
        invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
    } else {
        invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
    }
 
    // 到這裏 , 入參beanFactoryPostProcessors和容器中的全部BeanDefinitionRegistryPostProcessor已經所有處理完畢,
    // 下面開始處理容器中的全部BeanFactoryPostProcessor
 
    // Do not initialize FactoryBeans here: We need to leave all regular beans
    // uninitialized to let the bean factory post-processors apply to them!
    // 8.找出全部實現BeanFactoryPostProcessor接口的類
    String[] postProcessorNames =
            beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);
 
    // Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
    // Ordered, and the rest.
    // 用於存放實現了PriorityOrdered接口的BeanFactoryPostProcessor
    List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
    // 用於存放實現了Ordered接口的BeanFactoryPostProcessor的beanName
    List<String> orderedPostProcessorNames = new ArrayList<String>();
    // 用於存放普通BeanFactoryPostProcessor的beanName
    List<String> nonOrderedPostProcessorNames = new ArrayList<String>();
    // 8.1 遍歷postProcessorNames, 將BeanFactoryPostProcessor按實現PriorityOrdered、實現Ordered接口、普通三種區分開
    for (String ppName : postProcessorNames) {
        // 8.2 跳過已經執行過的
        if (processedBeans.contains(ppName)) {
            // skip - already processed in first phase above
        } else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
            // 8.3 添加實現了PriorityOrdered接口的BeanFactoryPostProcessor
            priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
        } else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
            // 8.4 添加實現了Ordered接口的BeanFactoryPostProcessor的beanName
            orderedPostProcessorNames.add(ppName);
        } else {
            // 8.5 添加剩下的普通BeanFactoryPostProcessor的beanName
            nonOrderedPostProcessorNames.add(ppName);
        }
    }
 
    // First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
    // 9.調用全部實現PriorityOrdered接口的BeanFactoryPostProcessor
    // 9.1 對priorityOrderedPostProcessors排序
    sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
    // 9.2 遍歷priorityOrderedPostProcessors, 執行postProcessBeanFactory方法
    invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
 
    // Next, invoke the BeanFactoryPostProcessors that implement Ordered.
    // 10.調用全部實現Ordered接口的BeanFactoryPostProcessor
    List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
    for (String postProcessorName : orderedPostProcessorNames) {
        // 10.1 獲取postProcessorName對應的bean實例, 添加到orderedPostProcessors, 準備執行
        orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
    }
    // 10.2 對orderedPostProcessors排序
    sortPostProcessors(orderedPostProcessors, beanFactory);
    // 10.3 遍歷orderedPostProcessors, 執行postProcessBeanFactory方法
    invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
 
    // Finally, invoke all other BeanFactoryPostProcessors.
    // 11.調用全部剩下的BeanFactoryPostProcessor
    List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
    for (String postProcessorName : nonOrderedPostProcessorNames) {
        // 11.1 獲取postProcessorName對應的bean實例, 添加到nonOrderedPostProcessors, 準備執行
        nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
    }
    // 11.2 遍歷nonOrderedPostProcessors, 執行postProcessBeanFactory方法
    invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
 
    // Clear cached merged bean definitions since the post-processors might have
    // modified the original metadata, e.g. replacing placeholders in values...
    // 12.清除元數據緩存（mergedBeanDefinitions、allBeanNamesByType、singletonBeanNamesByType），
    // 由於後處理器可能已經修改了原始元數據，例如， 替換值中的佔位符...
    beanFactory.clearMetadataCache();
}

細心的同窗可能會發現上方還出現了一個BeanDefinitionRegistryPostProcessor，這個東東實際上是BeanFactoryPostProcessor的特殊實習，觀察調用它的方法能夠看到它須要一個參數：BeanDefinitionRegistry，經過這個參數能夠更爲方便的去作一些自定義bean的操做3d

總結一下上方的邏輯：rest

  1. 將BeanFactoryPostProcessor和BeanDefinitionRegistryPostProcessor，分別放入兩個集合
  2. 分別進行排序處理
  3. 按照優先級分別調用invokeBeanDefinitionRegistryPostProcessors和invokeBeanFactoryPostProcessors方法
  4. 這兩個invoke方法相信你能夠想象的到無非就是循環調用這些實現類對應的方法

Spring的實現

查看這個接口的繼承體系，能夠看到這個接口的實現類是很是多的，各個實現類的功能若是感興趣你們能夠去慢慢挖掘一下 2code

1

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