将无Component注解的类加入spring容器

需求背景

旧项目没有用spring，现在想将项目的类交给spring管理。但是如果每个类都加@Component比较麻烦，希望能在不加Component情况下，也能将类交给spring管理。

比如如下路径的类

实战

1.定义注解

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface MyAnnotation {

    String value();
}
           

2.增加配置类，并使用该注解

注解的值表示需要被spring托管的包路径。其中Component表示该类需要被spring扫描到；BeanDefinitionReg的逻辑在第5步。

@Component
@MyAnnotation("com.enjoy.jack.pack.myclass")
@Import(BeanDefinitionReg.class)
public class MyPackage {
}
           

3.自定义扫描器

public class MyScanner extends ClassPathBeanDefinitionScanner {

    public MyScanner(BeanDefinitionRegistry registry) {
        super(registry);
    }

    @Override
    protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
        return super.doScan(basePackages);
    }
}
           

4.自定义过滤器

public class MyFilter implements TypeFilter {
    @Override
    public boolean match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory) throws IOException {
        return true;
    }
}
           

5.编写ImportBeanDefinitionRegistrar实现类

public class BeanDefinitionReg implements ImportBeanDefinitionRegistrar {

    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
        boolean res = importingClassMetadata.hasAnnotation("com.enjoy.jack.pack.MyAnnotation");
        if(!res){
            return;
        }
        Map<String, Object> map = importingClassMetadata.getAnnotationAttributes("com.enjoy.jack.pack.MyAnnotation");
        String packages = (String)map.get("value");
        MyScanner myScanner = new MyScanner(registry);
        myScanner.addIncludeFilter(new MyFilter());
        myScanner.doScan(packages);
    }
}
           

6.测试

@Test
    public void test2() {
        AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(MyPackage.class);
        Teacher bean = applicationContext.getBean(Teacher.class);
        System.out.println(bean.username);
    }