パッケージからクラスの一覧を取得するやつ

ClassesListUper.java

import java.io.IOException;
import java.net.URI;
import java.net.URISyntaxException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.List;

import static java.util.stream.Collectors.toList;

public class ClassesListUper {
    public List<Class<?>> classesOf(Package targetPackage) throws IOException, URISyntaxException {
        ClassLoader classLoader = Thread.currentThread()
                .getContextClassLoader();
        String packageDirectories = targetPackage.getName()
                .replace(".", "/");
        URI uri = classLoader.getResource(packageDirectories)
                .toURI();
        Path folder = Paths.get(uri);
        return Files.list(folder)
                .map(Path::getFileName)
                .map(this::toClassName)
                .map(name -> toClass(name, targetPackage))
                .collect(toList());
    }

    private String toClassName(Path filePath) {
        String name = filePath.getFileName().toString();
        return name.substring(0, name.lastIndexOf('.'));
    }

    private Class<?> toClass(String className, Package targetPackage) {
        try {
            String fqcn = targetPackage.getName() + "." + className;
            return Class.forName(fqcn);
        } catch (ClassNotFoundException e) {
            throw new RuntimeException(e);
        }
    }
}