聊聊、Spring自动扫描

一、项目

二、自定义注解

package org.rockcode.annotations;

import java.lang.annotation.*;

@Target(ElementType.TYPE)

@Retention(RetentionPolicy.RUNTIME)

@Documented

public @interface EnableFruit {

  String name() default "EnableFruit";

}

三、services 目录

package org.rockcode.services;

public interface Fruit {

public String getName();

}

package org.rockcode.services;

import org.rockcode.annotations.EnableFruit;

@EnableFruit

public class Apple implements Fruit{

 @Override public String getName() {

return "Apple";

 }

}

三、扫描services目录下面@EnableFruit的类

public class ClassPathEnableEnumScanner {

//解析路径下的 class

private static final PathMatchingResourcePatternResolver resolver = new PathMatchingResourcePatternResolver();

//转换成 MetaData 读取类

private static final SimpleMetadataReaderFactory register = new SimpleMetadataReaderFactory();

public static void getClazzFromAnnotation(String pkgPath, Class<? extends Annotation> annotationClass) {

//获取spring的包路径

String pathPackage = "classpath*:org/rockcode/services/**/*.class";

// 返回的是 FileSystemResource 数组

// file [E:\idea\SpringIOC\target\classes\org\rockcode\services\Apple.class]

// file [E:\idea\SpringIOC\target\classes\org\rockcode\services\Banana.class]

// file [E:\idea\SpringIOC\target\classes\org\rockcode\services\Fruit.class]

// file [E:\idea\SpringIOC\target\classes\org\rockcode\services\Orange.class]

Resource[] resources = new Resource[0];

try {

//加载路径下的资源

resources = resolver.getResources(pathPackage);

} catch (IOException e) {

}

for (int i = 0; i < resources.length; i++) {

Resource resource = resources[i];

MetadataReader metadataReader = null;

try {

//读取资源

// 返回 classMetadata annotationMetadata

metadataReader = register.getMetadataReader(resource);

} catch (IOException e) {

continue;

}

//读取资源的注解配置

AnnotationMetadata annotationMetadata = metadataReader.getAnnotationMetadata();

//判断是否包含注解，如果有则继续，没有就重新遍历

if (!annotationMetadata.hasAnnotation(annotationClass.getName())) continue;

//类信息

ClassMetadata classMetadata = metadataReader.getClassMetadata();

//类全名

String className = classMetadata.getClassName();

try {

//加载类

Class<?> clazz = Class.forName(className);

// 这里的逻辑是注册到 beanDefinitionMap，实现方式很多，通过 clazz 实例化对象，调用相关方法，等等

// todo

} catch (ClassNotFoundException e) {

e.printStackTrace();

}

}

}

public static void main(String[] args) {

getClazzFromAnnotation("org.rockcode.services", EnableFruit.class);

}

}

四、通过继承 ClassPathBeanDefinitionScanner 实现扫描器

在 Spring 体系中，ClassPathBeanDefinitionScanner 占有很重要的地位，如果要实现无 xml 化，就需要注解，有注解就需要自动扫描器。

package org.rockcode.scanner;

import org.rockcode.annotations.EnableFruit;

import org.springframework.beans.factory.support.BeanDefinitionRegistry;

import org.springframework.context.annotation.ClassPathBeanDefinitionScanner;

import org.springframework.context.support.GenericApplicationContext;

import org.springframework.core.type.filter.AnnotationTypeFilter;

public class MyClassPathBeanDefinitionScanner extends ClassPathBeanDefinitionScanner {

    public MyClassPathBeanDefinitionScanner(BeanDefinitionRegistry registry){

        super(registry,false);

    }

    public void registerTypeFilter(){

        addIncludeFilter(new AnnotationTypeFilter(EnableFruit.class));

    }

    public static void main(String[] args) {

        GenericApplicationContext context = new GenericApplicationContext();

        MyClassPathBeanDefinitionScanner myClassPathBeanDefinitionScanner = new MyClassPathBeanDefinitionScanner(context);

        myClassPathBeanDefinitionScanner.registerTypeFilter();

        myClassPathBeanDefinitionScanner.scan("org.rockcode.services");

        // 启动容器，也就是将扫描到的class实例化，并注册到beanFactory中，存入beanDefinitionMap

        context.refresh();

        //这里会拿到所有的bean实例

                String[] beanDefinitionNames = context.getBeanDefinitionNames();

        for (String beanDefinitionName : beanDefinitionNames) {

            System.out.println(context.getBean(beanDefinitionName));

        }

    }

}

巴特西

聊聊、Spring自动扫描

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