How Can I Runtime Scan Java Annotations for Dynamic Configuration?

Runtime Scanning of Java Annotations

In the development of Java libraries, it is often desirable to allow users to enhance their classes with custom annotations for various purposes. To utilize these annotations in a runtime context, it becomes necessary to scan the entire classpath for their presence.

One approach to achieve this is through the org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider API. This component provider scans the classpath for classes within a specified base package and applies configurable filters to identify candidate classes.

For instance, to search for classes annotated with a specific annotation, you can utilize the AnnotationTypeFilter class. Here is a code snippet demonstrating its usage:

ClassPathScanningCandidateComponentProvider scanner =
    new ClassPathScanningCandidateComponentProvider(false);

scanner.addIncludeFilter(new AnnotationTypeFilter(MyAnnotation.class));

for (BeanDefinition bd : scanner.findCandidateComponents(myBasePackage)) {
    System.out.println(bd.getBeanClassName());
}

In this example, the ClassPathScanningCandidateComponentProvider is configured to exclude default filters, ensuring that only classes annotated with @MyAnnotation are identified. The base package is specified in the findCandidateComponents method, and the results are printed to the console.

By leveraging this technique, you can effectively scan the Java classpath for annotated classes, enabling dynamic configuration and runtime handling of user-defined annotations.

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