How to get basePackages of #ComponentScan programatically at runtime? - spring-mvc

Question

The scanBasePackages of #SpringBootApplication configured as follow:
package com.xxx.boot.sample;
#SpringBootApplication(scanBasePackages = { "com.xxx.boot.sample", "com.xxx.boot.service" })
public class DemoApplication {
public static void main(String[] args) {
SpringApplication.run(DemoApplication.class, args);
}
}
The requirement is we want to integration Apache Dubbo component annotation scan with Spring Boot by programming at runtime for zero properties configuration, not by annotation.
#Configuration
#ConditionalOnClass({ EnableDubboConfig.class, AbstractConfig.class })
#ConditionalOnProperty(prefix = "dubbo", name = "enabled", havingValue = "true", matchIfMissing = true)
public class DubboAutoConfiguration {
/// Dubbo配置
#Configuration
#EnableDubboConfig
#ConditionalOnProperty(prefix = "dubbo.config", name = "enabled", havingValue = "true", matchIfMissing = true)
#EnableConfigurationProperties(DubboProperties.class)
public static class DubboConfigConfiguration {
}
/// Dubbo注解扫描
#Configuration
#ConditionalOnClass({ Service.class, Reference.class })
#ConditionalOnProperty(prefix = "dubbo.annotation", name = "enabled", havingValue = "true", matchIfMissing = true)
public static class DubboAnnotationConfiguration {
#Bean(name = "serviceAnnotationBeanPostProcessor")
#ConditionalOnMissingBean
public ServiceAnnotationBeanPostProcessor serviceAnnotationBeanPostProcessor(BeanFactory beanFactory) {
// 获取 Spring Boot 主入口类所在的包路径
List<String> packagesToScan = AutoConfigurationPackages.get(beanFactory);
if (packagesToScan == null) {
packagesToScan = Collections.emptyList();
}
return new ServiceAnnotationBeanPostProcessor(packagesToScan);
}
#Bean(name = ReferenceAnnotationBeanPostProcessor.BEAN_NAME)
#ConditionalOnMissingBean
public ReferenceAnnotationBeanPostProcessor referenceAnnotationBeanPostProcessor() {
return new ReferenceAnnotationBeanPostProcessor();
}
}
}
But AutoConfigurationPackages#get(BeanFactory) only return "com.xxx.boot.sample", not include "com.xxx.boot.service". I hope return all scanBasePackages value.
By debug, I found the #SpringBootApplication instance is a proxy class instance. I try to get Annotation use Class#getAnnotations, then get scanBasePackages field by reflection. But not success.
Question:
How to get scanBasePackages of #SpringBootApplication or basePackages of #ComponentScan programatically?

Answer 1

It isn't really advisable to try to reuse the scanBasePackages attributes for your own purposes. If you look at the source of #SpringBootApplication you'll see the following:
#AliasFor(annotation = ComponentScan.class, attribute = "basePackages")
String[] scanBasePackages() default {};
#AliasFor(annotation = ComponentScan.class, attribute = "basePackageClasses")
Class<?>[] scanBasePackageClasses() default {};
This is saying that these attributes are an alias for #ComponentScan. Since this annotation can be used on any #Configuration class it's actually legal to have many of them.
The #ComponentScan annotation triggers scanning by the ConfigurationClassParser. Look at the doProcessConfigurationClass method for all the gory details.
If you really want to find the annotation attributes yourself you can do the following:
applicationContext.getBeansWithAnnotation(ComponentScan.class).forEach((name, instance) -> {
Set<ComponentScan> scans = AnnotatedElementUtils.getMergedRepeatableAnnotations(instance.getClass(), ComponentScan.class);
for (ComponentScan scan : scans) {
System.out.println(Arrays.toString(scan.basePackageClasses()));
System.out.println(Arrays.toString(scan.basePackages()));
}
});
This will just get you those two values. You're still not considering any #Condition annotations or any include/exclude filters. You also won't deal with #ComponentScan() which means scan from the current package down.
What Spring Boot tends to do in these circumstances is define a new annotation for a specific purpose. For example, you can use #EntityScan to define where JPA entities are found. We then use AutoConfigurationPackages as the default value if you don't specify any override.