Spring自定义@enable注释元注释与@componentscan

Question

package com.example.package.app;

@SpringBootApplication
@com.example.annotations.EnableCustom("com.example.package.custom")
public class MyApplication {}

>

我不能使基本包属性是动态的，即我不能传递“com.example.package.base”，但需要在配置中预先定义包。

我查看了@aliasfor，但无法使其工作。

当我忽略基本包时，扫描从注释的定义包开始，而不是从注释类的包开始。在上面的示例中，它只扫描并创建com.example.annotations中类的bean，而不扫描并创建com.example.package.*中的bean。

如果将@componentscan(includeFilters=@componentscan.filter(type=filtertype.annotation,value=myAntation.class))放在MyApplication类上，则一切都可以工作，但当将其移动到@enableCustom的元注释时，将停止工作。如何告诉Spring Framework将@enableCustom视为使用某些默认值指定@componentscan的另一种方式。我尝试用@configuration、@component和其他方法对我的注释进行元注释，但没有成功：

@Configuration
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@ComponentScan(
        includeFilters = @ComponentScan.Filter(
                type = FilterType.ANNOTATION,
                value = ApplicationService.class))
public @interface EnableApplicationServices {
    @AliasFor(annotation = ComponentScan.class, attribute = "basePackages")
    String[] value() default {};
}

我在哪里可以找到这方面的文档，或者你会推荐什么起点？我的长期目标是拥有一个可以被大量项目使用的Spring Boot starter。

我们可以在以下存储库中找到M(N)：https://github.com/knittl/stackoverflow/tree/spring-enable-annotation

以下是包结构的概要：

// com.example.annotations.EnableCustom.java
@Configuration
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
// this annotation is never honored:
@ComponentScan(
        includeFilters = @ComponentScan.Filter(
                type = FilterType.ANNOTATION,
                value = MyAnnotation.class))
//@Import(EnableCustom.EnableCustomConfiguration.class)
public @interface EnableCustom {
    // this annotation works in combination with @Import, but scans the wrong packages.
    @ComponentScan(
            includeFilters = @ComponentScan.Filter(
                    type = FilterType.ANNOTATION,
                    value = MyAnnotation.class))
    class EnableCustomConfiguration {}
}

// file:com.example.app.Application.java
@SpringBootApplication
@EnableCustom("com.example.app.custom.services")
// @ComponentScan(
//         includeFilters = @ComponentScan.Filter(
//                 type = FilterType.ANNOTATION,
//                 value = MyAnnotation.class)) // <- this would work, but I want to move it to a custom annotation
public class Application {
}

// file:com.example.app.custom.services.MyService
@MyAnnotation
public class MyService {
    public MyService() {
        System.out.println("Look, I'm a bean now!");
    }
}

// file:com.example.annotations.services.WrongService.java
@MyAnnotation
public class WrongService {
    public WrongService() {
        System.out.println("I'm in the wrong package, I must not be instantiated");
    }
}

Answer 1

借助Fabio Formosa的答案、从这个答案中填写的缺失部分，以及@entityscan注释的一些启发，我终于成功地实现了这一点。可以在https://github.com/knittl/stackoverflow/tree/spring-enable-annotation-working找到一个可编译的工作示例。

简而言之：基于Fabio的回答，使用include筛选器正确配置ClassPathScanningCandidateComponentProvider实例，然后针对所有提供的基类运行它是很重要的。@aliasfor(annotation=import.class,…)似乎不是必需的，可以将其别名为另一个属性，例如相同注释的basePackages。

最低执行情况如下：

@Configuration
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Import(EnableCustom.EnableCustomConfiguration.class)
public @interface EnableCustom {
    @AliasFor(attribute = "basePackages")
    String[] value() default {};

    @AliasFor(attribute = "value")
    String[] basePackages() default {};

    class EnableCustomConfiguration implements ImportBeanDefinitionRegistrar, EnvironmentAware {
        private static final BeanNameGenerator BEAN_NAME_GENERATOR = AnnotationBeanNameGenerator.INSTANCE;
        private Environment environment;

        @Override
        public void setEnvironment(final Environment environment) {
            this.environment = environment;
        }

        @Override
        public void registerBeanDefinitions(
                final AnnotationMetadata metadata,
                final BeanDefinitionRegistry registry) {
            final AnnotationAttributes annotationAttributes = new AnnotationAttributes(
                    metadata.getAnnotationAttributes(EnableCustom.class.getCanonicalName()));

            final ClassPathScanningCandidateComponentProvider provider
                    = new ClassPathScanningCandidateComponentProvider(false, environment);
            provider.addIncludeFilter(new AnnotationTypeFilter(MyAnnotation.class, true));

            final Set<String> basePackages
                    = getBasePackages((StandardAnnotationMetadata) metadata, annotationAttributes);

            for (final String basePackage : basePackages) {
                for (final BeanDefinition beanDefinition : provider.findCandidateComponents(basePackage)) {
                    final String beanClassName = BEAN_NAME_GENERATOR.generateBeanName(beanDefinition, registry);
                    if (!registry.containsBeanDefinition(beanClassName)) {
                        registry.registerBeanDefinition(beanClassName, beanDefinition);
                    }
                }
            }
        }

        private static Set<String> getBasePackages(
                final StandardAnnotationMetadata metadata,
                final AnnotationAttributes attributes) {
            final String[] basePackages = attributes.getStringArray("basePackages");
            final Set<String> packagesToScan = new LinkedHashSet<>(Arrays.asList(basePackages));

            if (packagesToScan.isEmpty()) {
                // If value attribute is not set, fallback to the package of the annotated class
                return Collections.singleton(metadata.getIntrospectedClass().getPackage().getName());
            }

            return packagesToScan;
        }
    }
}