Spring-扫描注解原理,注解自动扫描原理分析

注解自动扫描原理分析

在spring的配置文件中加入如下代码,spring便开启了自动扫描,那么它的底层到底是如何实现的呢?

<context:component-scan base-package="com.wisely.highlight_spring4.ch1"/>

1. 首先找到解析这个标签的地方,spring 中解析具体的标签都有相应的解析器,且都继承了NamespaceHandlerSupport
   
   

2. 查看 ComponentScanBeanDefinitionParser的parse方法
   

3. 真正的逻辑其实是在ClassPathBeanDefinitionScanner的doScan方法中
   

4. 测试一下扫描过程

package com.wisely.highlight_spring4.ch1.di;

import java.io.IOException;
import java.util.LinkedHashSet;
import java.util.Set;

import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.context.annotation.ScannedGenericBeanDefinition;
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.MetadataReader;
import org.springframework.core.type.classreading.MetadataReaderFactory;
import org.springframework.core.type.classreading.SimpleMetadataReaderFactory;
import org.springframework.stereotype.Component;
import org.springframework.stereotype.Controller;
import org.springframework.stereotype.Service;

public class BeanFactoryTest
{
    public static void main(String[] args) throws IOException, ClassNotFoundException {
        Set<BeanDefinition> candidates = new LinkedHashSet<>();

        ResourcePatternResolver resourcePatternResolver = new PathMatchingResourcePatternResolver();  
        //这里特别注意一下类路径必须这样写
        //获取指定包下的所有类
        Resource[] resources = resourcePatternResolver.getResources("classpath*:com\wisely\highlight_spring4\ch1\di\*");  
         
        MetadataReaderFactory metadata=new SimpleMetadataReaderFactory();
        for(Resource resource:resources) {
            System.out.println(resource);
            MetadataReader metadataReader=metadata.getMetadataReader(resource);
            ScannedGenericBeanDefinition sbd = new ScannedGenericBeanDefinition(metadataReader);
            sbd.setResource(resource);
            sbd.setSource(resource);
            candidates.add(sbd);
        }
        for(BeanDefinition beanDefinition : candidates) {  
            String classname=beanDefinition.getBeanClassName();
            //扫描controller注解
            Controller c=Class.forName(classname).getAnnotation(Controller.class);
            //扫描Service注解
            Service s=Class.forName(classname).getAnnotation(Service.class);
            //扫描Component注解
            Component component=Class.forName(classname).getAnnotation(Component.class);
            if(c!=null ||s!=null ||component!=null){       
                System.out.println(classname);
            }
        } 
    }
}

5. 我的项目包结构
   

6. 控制台输出结果