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:

java 复制代码

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

	@Nullable
	default 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

java 复制代码

	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。

java 复制代码

    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

java 复制代码

@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<>();

    @Override
    public 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

java 复制代码

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

java 复制代码

@Slf4j
@Component
public class TestAProcessorOne implements DataProcessor{
    @Override
    public String getDataType() {
        return DataType.One;
    }

    @Override
    public void process(Object obj) {
        //对应的业务逻辑 TODO
        System.out.println("TestAProcessor processOne"+obj);
        
    }
}

java 复制代码

@Slf4j
@Component
public class TestAProcessorTwo implements DataProcessor{
    @Override
    public String getDataType() {
        return DataType.Two;
    }

    @Override
    public void process(Object obj) {
        //对应的业务逻辑 TODO
        System.out.println("TestAProcessor processTwo" + obj);
        
    }
}

4）测试工厂方法

java 复制代码

@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();
    }

}