Scanning Java Annotations At Runtime

Scanning Java annotations at runtime

Use org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider

API

A component provider that scans the classpath from a base package. It then applies exclude and include filters to the resulting classes to find candidates.

ClassPathScanningCandidateComponentProvider scanner =
new ClassPathScanningCandidateComponentProvider(<DO_YOU_WANT_TO_USE_DEFALT_FILTER>);

scanner.addIncludeFilter(new AnnotationTypeFilter(<TYPE_YOUR_ANNOTATION_HERE>.class));

for (BeanDefinition bd : scanner.findCandidateComponents(<TYPE_YOUR_BASE_PACKAGE_HERE>))
    System.out.println(bd.getBeanClassName());

run time annotation scanning when Dynamic class loading

This approach worked for me. hope this helps someone.

 DemoClass= (Class<Annotation>) Class.forName("com.this.class.DemoClass");
    if (method.isAnnotationPresent(DemoClass)) {
       for (Annotation annotation : method.getAnnotations()) {
       Class<? extends Annotation> annotationType = annotation.annotationType();      
       if (annotationType.getName() == "com.this.class.DemoClass") {
          for (Method annotationMethod : annotationType.getDeclaredMethods()) {
          value= annotationMethod.invoke(annotation, (Object[]) null);
          }
       }
     }

How can I find Annotated methods in Scala/Java on Runtime

Try one of classpath scanners based on Java reflection (e.g. Reflections) + scala-reflect. Since we use Java reflection only to look for classes and scala-reflect to look for annotated methods, annotations can be written in Scala.

import org.reflections.Reflections
import org.reflections.scanners.SubTypesScanner
import org.reflections.util.{ClasspathHelper, ConfigurationBuilder}
import scala.annotation.StaticAnnotation
import scala.jdk.CollectionConverters._
import scala.reflect.runtime.currentMirror
import scala.reflect.runtime.universe._

class printme extends StaticAnnotation

val reflections = new Reflections(
  (new ConfigurationBuilder)
    .setUrls(ClasspathHelper.forPackage(""))
    .setScanners(new SubTypesScanner(false))
)

def getAllAnnotated(): Unit =
  reflections.getAllTypes.asScala
    .flatMap(className =>
      currentMirror.classSymbol(Class.forName(className))
        .toType
        .decls
        .filter(symbol =>
          symbol.isMethod && symbol.annotations.exists(_.tree.tpe =:= typeOf[printme])
        )
        .map(method => s"$className.${method.name}")
    ).foreach(println)

Alternatives to Reflections library are for example ClassGraph and Burningwave. If we replace scala-reflect with Java reflection then annotation will have to be written in Java because only annotations written in Java are visible at runtime with Java reflection.

Java - loading annotated classes

First answer: Take a look at this project.

Reflections reflections = new Reflections("org.home.junk");
Set<Class<?>> annotated = reflections.getTypesAnnotatedWith(javax.persistence.Entity.class);

It returns all the classes from org.home.junk annotated with javax.persistence.Entity annotation.

Second Answer: To create new instance of above classes you can do this

for (Class<?> clazz : annotated) {
    final Object newInstance = clazz.newInstance();
}

Hope this answers everything.

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