Spring BeanPostProcessor

BeanPostProcessor源码原理

BeanPostProcessor接口在org.springframework.beans.factory.config包下，该接口源码如下:

public interface BeanPostProcessor {@Nullabledefault Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {return bean;}@Nullabledefault Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {return bean;}}

postProcessBeforeInitialization:前置处理器，在bean初始化之前被调用

postProcessAfterInitialization:后置处理器，在bean初始化之后被调用

用法：所有被Spring管理的Bean，被初始化前后都会调用，实现了BeanPostProcessor接口且被Spring管理的前置及后置处理器处理。

使用时机

当创建bean实例并完成属性填充之后，会调用AbstractAutowireCapableBeanFactory类的initializeBean方法对bean进行初始化，在初始化前后会分别执行postProcessBeforeInitialization方法和postProcessAfterInitialization

	protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {invokeAwareMethods(beanName, bean);Object wrappedBean = bean;if (mbd == null || !mbd.isSynthetic()) {wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);}try {invokeInitMethods(beanName, wrappedBean, mbd);}catch (Throwable ex) {throw new BeanCreationException((mbd != null ? mbd.getResourceDescription() : null), beanName, ex.getMessage(), ex);}if (mbd == null || !mbd.isSynthetic()) {wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);}return wrappedBean;}

再看一下applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName)的实现，getBeanPostProcessors()循环调用实现了BeanPostProcess的bean实例并执行processor.postProcessAfterInitialization(result, beanName)方法。

    public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)throws BeansException {Object result = existingBean;for (BeanPostProcessor processor : getBeanPostProcessors()) {Object current = processor.postProcessAfterInitialization(result, beanName);if (current == null) {return result;}result = current;}return result;}

BeanPostProcessor 应用场景

工厂模式中用于管理bean

1）自定义Bean管理器

@Slf4j
@Component
public class PluginManager implements BeanPostProcessor {//定义一个数据处理器Map，用于存储和数据类型绑定的数据处理器对象private static final Map<String, DataProcessor> dataProcessorMap = new HashMap<>();@Overridepublic Object postProcessAfterInitialization(@Nullable Object bean, @Nullable String beanName) throws BeansException {if (bean instanceof DataProcessor) {DataProcessor dp = (DataProcessor) bean;dataProcessorMap.put(dp.getDataType(), dp);log.info("PluginManager.postProcessAfterInitialization() | size={},dataProcessorMap={}", dataProcessorMap.size(), dataProcessorMap);}return bean;}public static DataProcessor getDataPlugin(String dataType) {return dataProcessorMap.get(dataType);}public static Map<String, DataProcessor> getDataProcessorMap(){return dataProcessorMap;}
}

2）自定义DataProcessor接口

public interface DataProcessor {//获取数据类型String getDataType();//实现对应数据类型的业务处理逻辑void process(Object obj);
}

3）自定义类实现DataProcess接口

@Slf4j
@Component
public class TestAProcessorOne implements DataProcessor{@Overridepublic String getDataType() {return DataType.One;}@Overridepublic void process(Object obj) {//对应的业务逻辑 TODOSystem.out.println("TestAProcessor processOne"+obj);}
}

@Slf4j
@Component
public class TestAProcessorTwo implements DataProcessor{@Overridepublic String getDataType() {return DataType.Two;}@Overridepublic void process(Object obj) {//对应的业务逻辑 TODOSystem.out.println("TestAProcessor processTwo" + obj);}
}

4）测试工厂方法

@RestController
public class TestController {@GetMapping("/test")public void test(){Map<String, DataProcessor> dataProcessorMap = PluginManager.getDataProcessorMap();System.out.println(dataProcessorMap);DataProcessor dataPlugin = PluginManager.getDataPlugin(DataType.One);System.out.println(dataPlugin);dataPlugin.process();}}