spring @Import 装配

1. 通过 @Import注解我们可以加载没有@Service @Component 注解的类到spring容器中

我们先看下 @Import的源码

我们可以通过实现这个接口自定义要加载的类

2.

package com.activity.study;

import java.net.URLClassLoader;
import java.util.List;

import org.springframework.context.annotation.ImportSelector;
import org.springframework.core.io.support.SpringFactoriesLoader;
import org.springframework.core.type.AnnotationMetadata;

public class UserSelector implements ImportSelector{

    @Override
    public String[] selectImports(AnnotationMetadata importingClassMetadata) {
        
//        List<String> strs = SpringFactoriesLoader.loadFactoryNames(EnableUser.class, URLClassLoader.getSystemClassLoader());
//        return strs.toArray(new String[] {});
        return new String[] {"com.activity.study.UserMeetting"};
    }

}

 返回要加载的类的路径即可.

然后我们就可以通过@Autowired注入Bean

3.

package com.activity.study;

import java.net.URLClassLoader;
import java.util.List;

import org.springframework.context.annotation.ImportSelector;
import org.springframework.core.io.support.SpringFactoriesLoader;
import org.springframework.core.type.AnnotationMetadata;

public class UserSelector implements ImportSelector{

    @Override
    public String[] selectImports(AnnotationMetadata importingClassMetadata) {
        
        List<String> strs = SpringFactoriesLoader.loadFactoryNames(EnableUser.class, URLClassLoader.getSystemClassLoader());
        return strs.toArray(new String[] {});
        //return new String[] {"com.activity.study.UserMeetting"};
    }

}

或者在 

resources 文件夹下面创建 META-INF/spring.factories 文件,

里面可以配置要注入的Bean

com.activity.study.EnableUser =
com.activity.study.UserMeetting

4.之后可以自定义注解加入@Import即可

package com.activity.study;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.springframework.context.annotation.Import;

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import({UserSelector.class})
public @interface EnableUser {

}

也可以直接在spring的启动类上加@Import,不过多个中间注解更简洁,也便于修改

@Enable的底层实现就是这样,最底层还是通过反射加载Class<?>类信息.