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; 2  3 import java.io.IOException; 4 import java.util.LinkedHashSet; 5 import java.util.Set; 6  7 import org.springframework.beans.factory.config.BeanDefinition; 8 import org.springframework.context.annotation.ScannedGenericBeanDefinition; 9 import org.springframework.core.io.Resource;10 import org.springframework.core.io.support.PathMatchingResourcePatteResolver;11 import org.springframework.core.io.support.ResourcePatteResolver;12 import org.springframework.core.type.classreading.MetadataReader;13 import org.springframework.core.type.classreading.MetadataReaderFactory;14 import org.springframework.core.type.classreading.SimpleMetadataReaderFactory;15 import org.springframework.stereotype.Component;16 import org.springframework.stereotype.Controller;17 import org.springframework.stereotype.Service;18 19 public class BeanFactoryTest20 {21 public static void main(String[] args) throws IOException, ClassNotFoundException {22 Set<BeanDefinition> candidates = new LinkedHashSet<>();23 24 ResourcePatteResolver resourcePatteResolver = new PathMatchingResourcePatteResolver();  25 //这里特别注意一下类路径必须这样写26 //获取指定包下的所有类27 Resource[] resources = resourcePatteResolver.getResources("classpath*:com\\wisely\\highlight_spring4\\ch1\\di\\*");  28  29 MetadataReaderFactory metadata=new SimpleMetadataReaderFactory();30 for(Resource resource:resources) {31 System.out.println(resource);32 MetadataReader metadataReader=metadata.getMetadataReader(resource);33 ScannedGenericBeanDefinition sbd = new ScannedGenericBeanDefinition(metadataReader);34 sbd.setResource(resource);35 sbd.setSource(resource);36 candidates.add(sbd);37 }38 for(BeanDefinition beanDefinition : candidates) {  39 String classname=beanDefinition.getBeanClassName();40 //扫描controller注解41 Controller c=Class.forName(classname).getAnnotation(Controller.class);42 //扫描Service注解43 Service s=Class.forName(classname).getAnnotation(Service.class);44 //扫描Component注解45 Component component=Class.forName(classname).getAnnotation(Component.class);46 if(c!=null ||s!=null ||component!=null){47 System.out.println(classname);48 }49 } 50 }51 }

 

5. 我的项目包结构
   

6. 控制台输出结果