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Spring后处理器详细介绍

tanglin_030907031026 人气:0

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:

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:

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:

分析:

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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