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Spring的后处理器-BeanFactoryPostprocessor

news 2025/8/26 13:48:30

Spring后处理器

Bean工厂后处理器-BeanFactoryPostProcessor

修改beanDefinition对象

添加beanDefiniton对象

方法一

方法二

自定义@Component

Spring后处理器

Spring后处理器是Spring对外开放的重要拓展点（让我们可以用添加自己的逻辑），允许我们介入到Bean的整个实例化流程中来，以达到动态注册BeanDefinition（向BeanDefitionMap中添加BeanDefition对象的过程），动态修改BeanDefition，以及动态修改Bean的作用。Spring主要有两种后处理器
- BeanFactoryPostprocessor：Bean工厂后处理器，（执行时机）在BeanDefinitionMap填充完毕，Bean实例化之前执行
- BeanPostProcessor：Bean后处理器，（执行时机）一般在Bean实例化后，填充到单例池singletonObjects之前执行

Bean工厂后处理器-BeanFactoryPostProcessor

BeanFactoryPostProcessor是一个接口规范，实现该接口的类只要交由Spring容器管理（即在配置文件中注册该类称为Bean对象）的话，那么Spring就会回调该接口的方法，用于对BeanDefition注册和修改功能

BeanFactoryPostProcessor定义如下

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//package org.springframework.beans.factory.config;import org.springframework.beans.BeansException;@FunctionalInterface
public interface BeanFactoryPostProcessor {void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException;
}

修改beanDefinition对象

创建一个实现类（修改beanDefinition对象）

package com.example.PostProcessor;import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;public class MyBeanFactoryPostProcessor implements BeanFactoryPostProcessor {@Overridepublic void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {System.out.println("beanDefinitionMap填充完毕后会回调该方法");// todo 修改Map集合中的BeanDefinition对象BeanDefinition userService = beanFactory.getBeanDefinition("userService");userService.setBeanClassName("com.example.DAO.Impl.UserDAOImpl");}
}

测试类

package com.example.Test;import org.springframework.context.support.ClassPathXmlApplicationContext;
public class TestApplicationContext {public static void main(String[] args)  {ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("application.xml");System.out.println(context.getBean("userService"));}
}

运行结果如下
- 显然bean对应的类被改变了

添加beanDefiniton对象

方法一

创建一个类（添加beanDefiniton对象）

package com.example.PostProcessor;import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.beans.factory.support.RootBeanDefinition;public class MyBeanFactoryPostProcessor implements BeanFactoryPostProcessor {@Overridepublic void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {// todo 向Map集合中添加一个BeanDefinition对象，即在配置文件中没有注册// 创建一个新的beanDefinition对象BeanDefinition beanDefinition = new RootBeanDefinition();// 设置bean对应的类beanDefinition.setBeanClassName("com.example.DAO.Impl.UserDAOImpl");DefaultListableBeanFactory listableBeanFactory = (DefaultListableBeanFactory) beanFactory;// 添加该beanDefinition对象listableBeanFactory.registerBeanDefinition("UserDAO", beanDefinition);}
}

在配置文件中没有配置UserDAO了

测试类

package com.example.Test;import com.example.DAO.Impl.UserDAOImpl;
import org.springframework.context.support.ClassPathXmlApplicationContext;public class TestApplicationContext {public static void main(String[] args) {ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("application.xml");System.out.println(context.getBean(UserDAOImpl.class));}
}

运行结果

beanDefinition对象成功添加

方法二

Spring提供了一个BeanFactoryPostProcessor的子接口BeanDefinitionRegistryPostProcessor专门用于注册BeanDefinition操作

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//package org.springframework.beans.factory.support;import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;public interface BeanDefinitionRegistryPostProcessor extends BeanFactoryPostProcessor {void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException;
}

创建一个类实现后处理器BeanFactoryPostProcessor的子接口BeanDefinitionRegistryPostProcessor（记得将该类注册到Spring容器中）

package com.example.PostProcessor;import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.beans.factory.support.RootBeanDefinition;public class MyBeanFactoryPostProcessor02 implements BeanDefinitionRegistryPostProcessor {@Overridepublic void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {// 注册beanDefinitionBeanDefinition beanDefinition = new RootBeanDefinition();beanDefinition.setBeanClassName("com.example.DAO.Impl.UserDAOImpl");registry.registerBeanDefinition("UserDAO", beanDefinition);}@Overridepublic void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {}
}

实现添加beanDefiniton就会简单很多

测试类

package com.example.Test;import com.example.DAO.Impl.UserDAOImpl;
import org.springframework.context.support.ClassPathXmlApplicationContext;public class TestApplicationContext {public static void main(String[] args) {ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("application.xml");System.out.println(context.getBean(UserDAOImpl.class));}
}

运行结果如下

完整流程图

自定义@Component

案例
- 使用Spring的BeanFactoryPostProcessor扩展点完成自定义注解扫描
要求
- 自定义@MyComponent注解，使用在类上
- 使用资料中提供好的包扫描工具BaseClassScanUtils完成指定包的类扫描
  - 工具类链接如下
  - https://hkm-web.oss-cn-beijing.aliyuncs.com/Utils
- 自定义BeanFactoryPostProcessor完成注解@MyComponent的解析，解析最终被Spring管理

具体代码如下

注解类

package com.example.Anno;import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;@Target(ElementType.TYPE) // 设该注解的使用范围
@Retention(RetentionPolicy.RUNTIME) // 设置该注解运行期间可见
public @interface MyComponent {String value(); //用于设置注解的值
}

工具类

package com.example.Utils;import com.example.Anno.MyComponent;
import org.springframework.core.io.Resource;
import org.springframework.core.io.support.PathMatchingResourcePatternResolver;
import org.springframework.core.io.support.ResourcePatternResolver;
import org.springframework.core.type.classreading.CachingMetadataReaderFactory;
import org.springframework.core.type.classreading.MetadataReader;
import org.springframework.core.type.classreading.MetadataReaderFactory;
import org.springframework.util.ClassUtils;import java.util.HashMap;
import java.util.Map;public class BaseClassScanUtils {//设置资源规则private static final String RESOURCE_PATTERN = "/**/*.class";public static Map<String, Class> scanMyComponentAnnotation(String basePackage) {//创建容器存储使用了指定注解的Bean字节码对象Map<String, Class> annotationClassMap = new HashMap<String, Class>();//spring工具类，可以获取指定路径下的全部类ResourcePatternResolver resourcePatternResolver = new PathMatchingResourcePatternResolver();try {String pattern = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX +ClassUtils.convertClassNameToResourcePath(basePackage) + RESOURCE_PATTERN;Resource[] resources = resourcePatternResolver.getResources(pattern);//MetadataReader 的工厂类MetadataReaderFactory refractory = new CachingMetadataReaderFactory(resourcePatternResolver);for (Resource resource : resources) {//用于读取类信息MetadataReader reader = refractory.getMetadataReader(resource);//扫描到的classString classname = reader.getClassMetadata().getClassName();Class<?> clazz = Class.forName(classname);//判断是否属于指定的注解类型if(clazz.isAnnotationPresent(MyComponent.class)){//获得注解对象MyComponent annotation = clazz.getAnnotation(MyComponent.class);//获得属value属性值String beanName = annotation.value();//判断是否为""if(beanName!=null&&!beanName.equals("")){//存储到Map中去annotationClassMap.put(beanName,clazz);continue;}//如果没有为"",那就把当前类的类名作为beanNameannotationClassMap.put(clazz.getSimpleName(),clazz);}}} catch (Exception exception) {}return annotationClassMap;}public static void main(String[] args) {Map<String, Class> stringClassMap = scanMyComponentAnnotation("com.itheima");System.out.println(stringClassMap);}
}

使用注解来注册为Bean对象的类

package com.example.Beans;import com.example.Anno.MyComponent;@MyComponent("otherBean")
public class otherBeans {
}

在配置文件中没有配置该类作为bean对象

后工厂处理器类（该类要交给Spring容器管理）

package com.example.PostProcessor;import com.example.Utils.BaseClassScanUtils;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;
import org.springframework.beans.factory.support.RootBeanDefinition;import java.util.Map;public class MyComponentBeanFactoryProcessor implements BeanDefinitionRegistryPostProcessor {@Overridepublic void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {// 通过工具去扫描指定包及其子包下的所有类，收集使用@MyComponent注解的类，放在Map集合中Map<String, Class> MyComponentAnnotationMap = BaseClassScanUtils.scanMyComponentAnnotation("com.example");// 遍历Map，组装BeanDefinition进行注册MyComponentAnnotationMap.forEach((beanName,clazz)->{// 获取beanClassNameString beanClassName = clazz.getName();// 创建beanDefinitionBeanDefinition beanDefinition = new RootBeanDefinition();beanDefinition.setBeanClassName(beanClassName);// 注册registry.registerBeanDefinition(beanName,beanDefinition);});}@Overridepublic void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {}
}

通过后工厂处理器类来将标记了自己创建的@MyComponent注解的类创建为beanDefinition对象后添加到beanDefinitionMap集合中。

测试类

package com.example.Test;import com.example.Beans.otherBeans;
import org.springframework.context.support.ClassPathXmlApplicationContext;public class TestApplicationContext {public static void main(String[] args) {ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("application.xml");System.out.println(context.getBean(otherBeans.class));}
}