Spring扩展点之BeanFactoryPostProcessor

逃离我推掉我的手 2024-04-18 22:48 80阅读 0赞

#### 前言 ####

`BeanFactoryPostProcessor`接口是Spring中一个非常重要的接口，它的接口定义如下

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 <td><pre>1 2 3 </pre></td> 
 <td><pre>public interface BeanFactoryPostProcessor {
 	void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException; } </pre></td> 
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 </tbody> 
</table>

当你实现了这个接口的时候，可以对还没有初始化的bean的属性进行修改或添加

#### `BeanFactoryPostProcessor`注册 ####

与`BeanPostProcessor`的统一注册不同，`BeanFactoryPostProcessor`的注册是留给具体的业务实现的。它的维护是在`AbstractApplicationContext`类中

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 <td><pre>1 2 3 4 5 6 7 </pre></td> 
 <td><pre> private final List&lt;BeanFactoryPostProcessor&gt; beanFactoryPostProcessors = new ArrayList&lt;&gt;(); 	public void addBeanFactoryPostProcessor(BeanFactoryPostProcessor postProcessor) {
 		Assert.notNull(postProcessor, "BeanFactoryPostProcessor must not be null"); 		this.beanFactoryPostProcessors.add(postProcessor); 	} </pre></td> 
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#### 执行原理 ####

调用逻辑在`AbstractApplicationContext.invokeBeanFactoryPostProcessors`方法中  
这个方法比较长，可以重点关注我添加注释的地方

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 <td><pre>1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 </pre></td> 
 <td><pre> protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
 		PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors()); 		if (beanFactory.getTempClassLoader() == null &amp;&amp; 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&lt;BeanFactoryPostProcessor&gt; beanFactoryPostProcessors) {
 Set&lt;String&gt; processedBeans = new HashSet&lt;String&gt;(); // 1.判断beanFactory是否为BeanDefinitionRegistry，在这里普通的beanFactory是DefaultListableBeanFactory,而DefaultListableBeanFactory实现了BeanDefinitionRegistry接口，因此这边为true if (beanFactory instanceof BeanDefinitionRegistry) {
 BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory; List&lt;BeanFactoryPostProcessor&gt; regularPostProcessors = new LinkedList&lt;BeanFactoryPostProcessor&gt;(); List&lt;BeanDefinitionRegistryPostProcessor&gt; registryProcessors = new LinkedList&lt;BeanDefinitionRegistryPostProcessor&gt;(); // 2.处理入参beanFactoryPostProcessors for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
 if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
 BeanDefinitionRegistryPostProcessor registryProcessor = (BeanDefinitionRegistryPostProcessor) postProcessor; // 如果是BeanDefinitionRegistryPostProcessor则直接执行BeanDefinitionRegistryPostProcessor接口的postProcessBeanDefinitionRegistry方法 registryProcessor.postProcessBeanDefinitionRegistry(registry); registryProcessors.add(registryProcessor); } else {
 regularPostProcessors.add(postProcessor); } } List&lt;BeanDefinitionRegistryPostProcessor&gt; currentRegistryProcessors = new ArrayList&lt;BeanDefinitionRegistryPostProcessor&gt;(); // 3找出所有实现BeanDefinitionRegistryPostProcessor接口的Bean的beanName String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false); for (String ppName : postProcessorNames) {
 // 校验是否实现了PriorityOrdered接口 if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
 // 获取对应的bean实例, 添加到currentRegistryProcessors中, currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class)); processedBeans.add(ppName); } } // 排序(根据是否实现PriorityOrdered、Ordered接口和order值来排序) sortPostProcessors(currentRegistryProcessors, beanFactory); registryProcessors.addAll(currentRegistryProcessors); // 遍历currentRegistryProcessors, 执行postProcessBeanDefinitionRegistry方法 invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry); // 清空currentRegistryProcessors currentRegistryProcessors.clear(); // 4.与上边3的流程差不多，这是这里处理的是实现Ordered接口 postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false); for (String ppName : postProcessorNames) {
 if (!processedBeans.contains(ppName) &amp;&amp; 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.调用所有剩下的BeanDefinitionRegistryPostProcessors boolean reiterate = true; while (reiterate) {
 reiterate = false; // 找出所有实现BeanDefinitionRegistryPostProcessor接口的类 postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false); for (String ppName : postProcessorNames) {
 // 跳过已经执行过的 if (!processedBeans.contains(ppName)) {
 currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class)); processedBeans.add(ppName); reiterate = true; } } sortPostProcessors(currentRegistryProcessors, beanFactory); registryProcessors.addAll(currentRegistryProcessors); // 5遍历currentRegistryProcessors, 执行postProcessBeanDefinitionRegistry方法 invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry); currentRegistryProcessors.clear(); } // 6.调用所有BeanDefinitionRegistryPostProcessor的postProcessBeanFactory方法 invokeBeanFactoryPostProcessors(registryProcessors, beanFactory); // 7.最后, 调用入参beanFactoryPostProcessors中的普通BeanFactoryPostProcessor的postProcessBeanFactory方法 invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory); } else {
 invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory); } // 到这里 , 入参beanFactoryPostProcessors和容器中的所有BeanDefinitionRegistryPostProcessor已经全部处理完毕, // 下面开始处理容器中的所有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.找出所有实现BeanFactoryPostProcessor接口的类 String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false); // Separate between BeanFactoryPostProcessors that implement PriorityOrdered, // Ordered, and the rest. // 用于存放实现了PriorityOrdered接口的BeanFactoryPostProcessor List&lt;BeanFactoryPostProcessor&gt; priorityOrderedPostProcessors = new ArrayList&lt;BeanFactoryPostProcessor&gt;(); // 用于存放实现了Ordered接口的BeanFactoryPostProcessor的beanName List&lt;String&gt; orderedPostProcessorNames = new ArrayList&lt;String&gt;(); // 用于存放普通BeanFactoryPostProcessor的beanName List&lt;String&gt; nonOrderedPostProcessorNames = new ArrayList&lt;String&gt;(); // 8.1 遍历postProcessorNames, 将BeanFactoryPostProcessor按实现PriorityOrdered、实现Ordered接口、普通三种区分开 for (String ppName : postProcessorNames) {
 // 8.2 跳过已经执行过的 if (processedBeans.contains(ppName)) {
 // skip - already processed in first phase above } else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
 // 8.3 添加实现了PriorityOrdered接口的BeanFactoryPostProcessor priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class)); } else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
 // 8.4 添加实现了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.调用所有实现PriorityOrdered接口的BeanFactoryPostProcessor // 9.1 对priorityOrderedPostProcessors排序 sortPostProcessors(priorityOrderedPostProcessors, beanFactory); // 9.2 遍历priorityOrderedPostProcessors, 执行postProcessBeanFactory方法 invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory); // Next, invoke the BeanFactoryPostProcessors that implement Ordered. // 10.调用所有实现Ordered接口的BeanFactoryPostProcessor List&lt;BeanFactoryPostProcessor&gt; orderedPostProcessors = new ArrayList&lt;BeanFactoryPostProcessor&gt;(); for (String postProcessorName : orderedPostProcessorNames) {
 // 10.1 获取postProcessorName对应的bean实例, 添加到orderedPostProcessors, 准备执行 orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class)); } // 10.2 对orderedPostProcessors排序 sortPostProcessors(orderedPostProcessors, beanFactory); // 10.3 遍历orderedPostProcessors, 执行postProcessBeanFactory方法 invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory); // Finally, invoke all other BeanFactoryPostProcessors. // 11.调用所有剩下的BeanFactoryPostProcessor List&lt;BeanFactoryPostProcessor&gt; nonOrderedPostProcessors = new ArrayList&lt;BeanFactoryPostProcessor&gt;(); for (String postProcessorName : nonOrderedPostProcessorNames) {
 // 11.1 获取postProcessorName对应的bean实例, 添加到nonOrderedPostProcessors, 准备执行 nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class)); } // 11.2 遍历nonOrderedPostProcessors, 执行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.清除元数据缓存（mergedBeanDefinitions、allBeanNamesByType、singletonBeanNamesByType）， // 因为后处理器可能已经修改了原始元数据，例如， 替换值中的占位符... beanFactory.clearMetadataCache(); } </pre></td> 
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细心的同学可能会发现上方还出现了一个`BeanDefinitionRegistryPostProcessor`，这个东东其实是`BeanFactoryPostProcessor`的特殊实习，观察调用它的方法可以看到它需要一个参数：`BeanDefinitionRegistry`，通过这个参数可以更为方便的去做一些自定义bean的操作

总结一下上方的逻辑：

1.  将`BeanFactoryPostProcessor`和`BeanDefinitionRegistryPostProcessor`，分别放入两个集合
2.  分别进行排序处理
3.  按照优先级分别调用`invokeBeanDefinitionRegistryPostProcessors`和`invokeBeanFactoryPostProcessors`方法
4.  这两个invoke方法相信你可以想象的到无非就是循环调用这些实现类对应的方法

#### Spring的实现 ####

查看这个接口的继承体系，可以看到这个接口的实现类是非常多的，各个实现类的功能如果感兴趣大家可以去慢慢挖掘一下

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