使用Spring的BeanFactoryPostProcessor扩展点完成自定义注解扫描
一、概述
本次实验是上一次https://blog.csdn.net/2301_80749359/article/details/157651601?fromshare=blogdetail&sharetype=blogdetail&sharerId=157651601&sharerefer=PC&sharesource=2301_80749359&sharefrom=from_link的扩展，只是加了自定义注解较为方便。
二、具体步骤
2.1创建自定义注解
java
package com.itheima.ano;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
//设定在哪些类型上可以使用
@Target(ElementType.TYPE)
//设定作用的范围
@Retention(RetentionPolicy.RUNTIME)
public @interface MyComponent {
// 配置value属性，以代表bean的名字
String value();
}2.2引入扫描注解包的工具类
java
package com.itheima.utils;
import com.itheima.ano.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.itheima");
System.out.println(stringClassMap);
}
}2.3利用工具类扫描包
利用工具类扫描包（包括该包及其子包下）中带有@MyComponent注释的类，然后遍历Map进行相关的操作（具体见代码注释）
java
package com.itheima.processor;
import com.itheima.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 {
//先是使用扫描的工具进行扫描
Map<String, Class> myComponentAnnotationMap = BaseClassScanUtils.scanMyComponentAnnotation("com.itheima");
// 然后是遍历这个map，得到bbeanDefinition
myComponentAnnotationMap.forEach((beanName,beanClass)->{
// 先是获取到全限制名(转为String类型的)
String className = beanClass.getName();
// 然后是定义bbeanDefinition
BeanDefinition beanDefinition = new RootBeanDefinition();
beanDefinition.setBeanClassName(className);
// 再是进行注册，这就是放到单例池单中了
beanDefinitionRegistry.registerBeanDefinition(beanName,beanDefinition);
});
}
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory configurableListableBeanFactory) throws BeansException {
}
}2.4测试：
java
package com.itheima.test;
import com.alibaba.druid.pool.DruidDataSource;
import com.itheima.beans.OthrerBean;
import com.itheima.beans.Xxxbean;
import com.itheima.dao.impl.UserDaoImpl;
import com.itheima.dao.personDao;
import com.itheima.service.UserService;
import com.mysql.jdbc.Connection;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.beans.factory.xml.XmlBeanDefinitionReader;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import javax.xml.bind.annotation.XmlAccessOrder;
import java.io.IOException;
import java.io.InputStream;
import java.sql.DriverManager;
public class BeanFactoryTest {
public static void main(String[] args) throws Exception {
ApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext_beanfac.xml");
OthrerBean othrerBean = (OthrerBean) applicationContext.getBean("otherBean");
System.out.println(othrerBean);
}
}结果：
