ClassScanner.java

package io.kaif.web.v1;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import org.springframework.core.io.Resource;
import org.springframework.core.io.support.PathMatchingResourcePatternResolver;
import org.springframework.core.io.support.ResourcePatternResolver;
import org.springframework.core.type.classreading.CachingMetadataReaderFactory;
import org.springframework.core.type.classreading.MetadataReader;
import org.springframework.core.type.classreading.MetadataReaderFactory;
import org.springframework.util.ClassUtils;
import org.springframework.util.SystemPropertyUtils;

/**
 * see http://stackoverflow.com/questions/1456930/how-do-i-read-all-classes-from-a-java-package-in-the-classpath
 */
public class ClassScanner {
  public static List<Class> searchAnnotatedClasses(String basePackage, Class<?> annotation)
      throws IOException, ClassNotFoundException {
    ResourcePatternResolver resourcePatternResolver = new PathMatchingResourcePatternResolver();
    MetadataReaderFactory metadataReaderFactory = new CachingMetadataReaderFactory(
        resourcePatternResolver);

    List<Class> candidates = new ArrayList<>();
    String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX +
        resolveBasePackage(basePackage) + "/" + "**/*.class";
    Resource[] resources = resourcePatternResolver.getResources(packageSearchPath);
    for (Resource resource : resources) {
      if (resource.isReadable()) {
        MetadataReader metadataReader = metadataReaderFactory.getMetadataReader(resource);
        if (isCandidate(metadataReader, annotation)) {
          candidates.add(Class.forName(metadataReader.getClassMetadata().getClassName()));
        }
      }
    }
    return candidates;
  }

  private static String resolveBasePackage(String basePackage) {
    return ClassUtils.convertClassNameToResourcePath(SystemPropertyUtils.resolvePlaceholders(
        basePackage));
  }

  @SuppressWarnings("unchecked")
  private static boolean isCandidate(MetadataReader metadataReader, Class<?> annotation)
      throws ClassNotFoundException {
    try {
      Class c = Class.forName(metadataReader.getClassMetadata().getClassName());
      if (c.getAnnotation(annotation) != null) {
        return true;
      }
    } catch (Throwable e) {
    }
    return false;
  }
}