Spring后处理器详细介绍
作者:tanglin_030907031026
一、概述
Spring的后处理器是Spring对外开发的重要扩展点、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, 动态修改BeanDefinition, 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, 在BeanDefinitionMap填充完毕, Bean实例化之前执行;
- BeanPostProcessor:Bean后处理器, 一般在Bean实例化之后, 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, 实现了该接口的类只要交由Spring容器管理的话, 那么Spring就会回调该接口的方法, 用于对BeanDefinition注册和修改的功能。
BeanFactoryPostProcessor定义如下:
public interface BeanFactoryPostProcessor{ void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) ; }
二、案例演示
①:注册BeanDefinition
1.编写MyBeanFactoryPostProcessor类,实现BeanFactoryPostProcessor接口,并实现接口方法
package com.tangyuan.processor; 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 { @Override public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException { System.out.println("beanDefinitionMap填充完毕后回调该方法"); //不在主xml文件中进行配置bean //动态注册Beandifinition BeanDefinition beanDefinition=new RootBeanDefinition(); beanDefinition.setBeanClassName("com.tangyuan.dao.impl.PeresonDaoImpl"); System.out.println(beanFactory); //org.springframework.beans.factory.support.DefaultListableBeanFactory@737996a0: defining beans //强转成DefaultListableBeanFactory DefaultListableBeanFactory defaultListableBeanFactory= (DefaultListableBeanFactory) beanFactory; defaultListableBeanFactory.registerBeanDefinition("PersonDao",beanDefinition); } }
2.测试
//创建ApplicationContext,加载配置文件,实例化容器 ClassPathXmlApplicationContext applicationContext=new ClassPathXmlApplicationContext("applicationContext.xml"); PeresonDao bean = applicationContext.getBean(PeresonDao.class); System.out.println(bean);//com.tangyuan.dao.impl.PeresonDaoImpl@6ddf90b0
②:注册BeanDefinition
Spring提供了一个BeanFactoryPostProcessor的子接BeanDefinitionRegistryPostProcessor专门用于注册BeanDefinition操作
public class MyBeanFactoryPostProcessor2 implements BeanDefinitionRegistryPostProcessor{ @Override public void postProcessBeanFactory(ConfigurableListableBeanFactory configurableListableBeanFactory) throws BeansException{} @Override public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry beanDefinitionRegistry) throws BeansException{ BeanDefinition beanDefinition=new RootBeanDefinition() ; beanDefinition.setBeanClassName("com.tangyuan.dao.UserDaoImp12"); beanDefinitionRegistry.registerBeanDefinition("userDao2",beanDefinition) ; } }
案例演示:
1.编写MyBeanDefinitionRegistryPostProcessor类,实现BeanDefinitionRegistryPostProcessor接口,并实现接口方法
package com.tangyuan.processor; import com.alibaba.druid.support.spring.stat.SpringStatUtils; 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; public class MyBeanDefinitionRegistryPostProcessor implements BeanDefinitionRegistryPostProcessor { @Override public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry beanDefinitionRegistry) throws BeansException { System.out.println("MyBeanDefinitionRegistryPostProcessor的postProcessBeanDefinitionRegistry方法"); //向容器当中注册BeanDefinition BeanDefinition beanDefinition=new RootBeanDefinition(); beanDefinition.setBeanClassName("com.tangyuan.dao.impl.PeresonDaoImpl"); beanDefinitionRegistry.registerBeanDefinition("PersonDao",beanDefinition); } @Override public void postProcessBeanFactory(ConfigurableListableBeanFactory configurableListableBeanFactory) throws BeansException { System.out.println("MyBeanDefinitionRegistryPostProcessor的postProcessBeanFactory方法"); } }
2.将MyBeanDefinitionRegistryPostProcessor类在xml文件中进行配置
<bean class="com.tangyuan.processor.MyBeanDefinitionRegistryPostProcessor"></bean>
3.测试
//创建ApplicationContext,加载配置文件,实例化容器 ClassPathXmlApplicationContext applicationContext=new ClassPathXmlApplicationContext("applicationContext.xml"); PeresonDao bean = applicationContext.getBean(PeresonDao.class); System.out.println(bean);//com.tangyuan.dao.impl.PeresonDaoImpl@5a8e6209
ps:方法的执行顺序
1.MyBeanDefinitionRegistryPostProcessor的postProcessBeanDefinitionRegistry方法
2.MyBeanDefinitionRegistryPostProcessor的postProcessBeanFactory方法
3.MyBeanFactoryPostProcessor的postProcessBeanFactory方法
③:使用Spring的BeanFactoryPostProcessor扩展点完成自定义注解扫描
要求如下:
- 自定义@MyComponent注解, 使用在类上;
- 使用资料中提供好的包扫描器工具BaseClassScanUtils完成指定包的类扫描;
- 自定义BeanFactoryPostProcessor完成注解@MyComponent的解析, 解析后最终被Spring管理。
1.创建一个OtherBean类,并定义@MyComponent注解
package com.tangyuan.beans; import com.tangyuan.anno.MyComponent; @MyComponent("OtherBean") public class OtherBean { }
package com.tangyuan.anno; import java.lang.annotation.ElementType; import java.lang.annotation.Retention; import java.lang.annotation.RetentionPolicy; import java.lang.annotation.Target; @Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) public @interface MyComponent { String value(); }
2.BaseClassScanUtils 帮助类编写
package com.tangyuan.utils; import com.tangyuan.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.lang.annotation.Annotation; import java.util.HashMap; import java.util.List; 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class String 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beanName annotationClassMap.put(clazz.getSimpleName(),clazz); } } } catch (Exception exception) { } return annotationClassMap; } public static void main(String[] args) { Map<String, Class> stringClassMap = scanMyComponentAnnotation("com.tangyuan"); System.out.println(stringClassMap); } }
3.编写MyComponentBeanFactoryPostProcessor类,并实现BeanDefinitionRegistryPostProcessor接口
package com.tangyuan.processor; import com.tangyuan.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 MyComponentBeanFactoryPostProcessor implements BeanDefinitionRegistryPostProcessor { @Override public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry beanDefinitionRegistry) throws BeansException { //通过扫描工具去扫描指定包及其包下的所有类,收集使用@MyComponent注解的类 Map<String, Class> map = BaseClassScanUtils.scanMyComponentAnnotation( "com.tangyuan" ); //循环遍历,组装BeanDefinition进行注册 map.forEach((beanName,clazz)->{ //获取BeanClassName String name = clazz.getName();//com.tangyuan.beans.OtherBean //创建BeanDefinition BeanDefinition beanDefinition=new RootBeanDefinition(); beanDefinition.setBeanClassName(name); //注册 beanDefinitionRegistry.registerBeanDefinition(name,beanDefinition); }); } @Override public void postProcessBeanFactory(ConfigurableListableBeanFactory configurableListableBeanFactory) throws BeansException { } }
4.在xml文件编写MyComponentBeanFactoryPostProcessor类的bean
<bean class="com.tangyuan.processor.MyComponentBeanFactoryPostProcessor"></bean>
5.测试
OtherBean bean1 = applicationContext.getBean(OtherBean.class); System.out.println(bean1);//com.tangyuan.beans.OtherBean@1877ab81
6.编写一个BookBean类,并实现@MyComponent注解
package com.tangyuan.beans; import com.tangyuan.anno.MyComponent; import org.springframework.stereotype.Component; @MyComponent("BookBean") public class BookBean { }
7.再次测试
//创建ApplicationContext,加载配置文件,实例化容器 ClassPathXmlApplicationContext applicationContext=new ClassPathXmlApplicationContext("applicationContext.xml"); BookBean bean2 = applicationContext.getBean(BookBean.class); System.out.println(bean2);//com.tangyuan.beans.BookBean@1877ab81
三、Bean的后处理器BeanPostProcessor
Bean被实例化后, 到最终缓存到名为singletonObjects单例池之前, 中间会经过Bean的初始化过程, 例如:属性的 填充、初始方法init的执行等, 其中有一个对外进行扩展的点BeanPostProcessor,我们称为Bean后处理。跟上面的 Bean工厂后处理器相似, 它也是一个接口, 实现了该接口并被容器管理的BeanPostProcessor, 会在流程节点上被 Spring自动调用。
BeanPostProcessor的接口定义如下:
public interface BeanPostProcessor{ @Nullable //在属性注入完毕, init初始化方法执行之前被回调 default Object postProcesBeforeInitialization(Object bean, String bean Name)throws BeansException{ return bean; } //在初始化方法执行之后, 被添加到单例池singletonObjects之前被回调 @Nullable default Object postProcessAfterInitialization(Object bean, String bean Name) throws BeansException{ return bean; } }
案例:对Bean方法进行执行时间日志增强
要求如下:
- Bean的方法执行之前控制台打印当前时间;
- Bean的方法执行之后控制台打印当前时间。
分析:
- 对方法进行增强主要就是代理设计模式和包装设计模式;
- 由于Bean方法不确定, 所以使用动态代理在运行期间执行增强操作;
- 在Bean实例创建完毕后, 进入到单例池之前, 使用Proxy代替真是的目标Bean
思路:编写BeanPostProcessor, 增强逻辑编写在after方法中
public Object post Process After Initialization(Object bean,String beanName) throws BeansException{ //Bean进行动态代理,返回的是Proxy代理对象 Object proxy Bean=Proxy.newProxyInstance(bean.getClass() .getClassLoader() , bean.getClass() .getInterfaces() , (Object proxy, Method method,Object[] args) ->{ long start=System.currentTimeMillis() ; system.out.println("开始时间:"+new Date(start) ) ; //执行目标方法BIN Object result=method.invoke(bean,args) ; long end=System.currentTimeMillis() ; System.out.println("结束时间:"+new Date(end) ) ; return result; }); //返回代理对象 return proxy Bean; }
实现代码如下:
1.编写一个TimeLogBeanPostProcessor类,接口BeanPostProcessor实现,方法也实现
package com.tangyuan.processor; import org.springframework.beans.BeansException; import org.springframework.beans.factory.config.BeanPostProcessor; import java.lang.reflect.InvocationHandler; import java.lang.reflect.Method; import java.lang.reflect.Proxy; import java.util.Date; public class TimeLogBeanPostProcessor implements BeanPostProcessor { @Override public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException { return null; } @Override public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException { //使用动态代理对目标Bean进行增强,返回proxy对象,进而存储到单例池singletonObjects中 Object beanProxy= Proxy.newProxyInstance( bean.getClass().getClassLoader(), bean.getClass().getInterfaces(), new InvocationHandler() { @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { //1.输出开始时间 System.out.println("方法:"+method.getName()+"-开始时间:"+new Date()); //2.执行目标方法 Object invoke = method.invoke(bean, args); //3.输出结束时间 System.out.println("方法:"+method.getName()+"-结束时间:"+new Date()); return invoke; } } ); return beanProxy; } }
2.在xml文件上完成对TimeLogBeanPostProcessor类的配置
<bean class="com.tangyuan.processor.TimeLogBeanPostProcessor"></bean>
3.编写方法
package com.tangyuan.dao; public interface UserDao { void show(); }
package com.tangyuan.dao.impl; import com.tangyuan.dao.UserDao; import org.springframework.beans.factory.InitializingBean; public class UserDaoImpl implements UserDao , InitializingBean { public UserDaoImpl() { System.out.println("UserDao实例化"); } public void init(){ System.out.println("init初始化方法执行"); } @Override public void afterPropertiesSet() throws Exception { System.out.println("属性设置之后执行~~~~"); } @Override public void show() {//ctrl+Alt+t try { Thread.sleep(3000); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("show....."); } }
4.测试
//创建ApplicationContext,加载配置文件,实例化容器
ClassPathXmlApplicationContext applicationContext=new ClassPathXmlApplicationContext("applicationContext.xml");
UserDao dao = (UserDao) applicationContext.getBean("userDao");
dao.show();
方法:show-开始时间:Tue Nov 29 10:21:31 GMT+08:00 2022
show.....
方法:show-结束时间:Tue Nov 29 10:21:31 GMT+08:00 2022
四、Spring ioc整体流程总结
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