ClassPathScanning.java

package org.eron;

import java.io.File;
import java.io.IOException;
import java.lang.annotation.Annotation;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Parameter;
import java.net.MalformedURLException;
import java.net.URISyntaxException;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Enumeration;
import java.util.Iterator;

public class Main {

    public static void main(String[] args) throws IOException, URISyntaxException {
        // GET ALL CLASSPATH LOCATIONS
        Enumeration<URL> resources = ClassLoader.getSystemClassLoader().getResources("");
        Iterator<URL> urlIterator = resources.asIterator();

        // ITERATE ON THESE LOCATIONS AND TAKE ONLY CLASS FILES AND PREFIX BEFORE PACKAGE DIR
        ArrayList<File> files = null;
        String dir = null;
        while(urlIterator.hasNext()){
            dir = urlIterator.next().getFile();
            File file1 = new File(dir);
            files = iteratorScan(file1);
        }
        final String dirFinal = dir;

        // INSTANTIATE NEW CLASSLOADER, SPECIFICATING FILE PROTOCOL AND POINTING TO THE FOLDER WHERE PACKAGE
        // IS LOCATED
        URLClassLoader urlClassLoader = new URLClassLoader(new URL[]{
                new URL(dirFinal.startsWith("file:") ? dirFinal : "file:" + dirFinal)
        });

        // ITERATE FOR ALL CLASSES AND DO THE OPERATIONS
        files.forEach(file ->{
            try {
                // GET THE ABSOLUTE PATH OF CLASS FILE AND REMOVE THE PATH BEFORE PACKAGE, THE ".class" EXTENSION AND
                // REPLACE "/" FOR "."
                String fullQualifiedName = file.getAbsolutePath()
                        .replace(dirFinal, "")
                        .replace(".class", "").replace("/", ".");

                // LOAD THE CLASS
                Class<?> aClass = urlClassLoader.loadClass(fullQualifiedName);

                // INSTANTIATE AND TEST CLASS
                if(aClass.getName().endsWith("Logger")){
                    Object[] test = new Object[1];
                    Arrays.stream(aClass.getConstructors()).forEach(constructor -> {
                        Parameter[] parameters = constructor.getParameters();
                        if(parameters.length == 0){
                            try{
                                test[0] = constructor.newInstance();
                            } catch (InvocationTargetException e) {
                                throw new RuntimeException(e);
                            } catch (InstantiationException e) {
                                throw new RuntimeException(e);
                            } catch (IllegalAccessException e) {
                                throw new RuntimeException(e);
                            }
                        }
                    });
                    Logger log = (Logger) test[0];
                    try{
                        log.log("Testing");
                        log.log("Anyways again");
                    } catch(NullPointerException ex){}
                }

                // OBLIGATORY TRY/CATCH BLOCK FOR POSSIBLE EXCEPTIONS
            } catch (ClassNotFoundException e) {
                throw new RuntimeException(e);
            }
        });
    }

    public static ArrayList<File> iteratorScan(File dirOrF){
        ArrayList<File> files = new ArrayList<>();
        Arrays.stream(dirOrF.listFiles()).forEach(f -> {
            if (f.isDirectory()){
                iteratorScan(f).forEach(files::add);
            } else {
                files.add(f);
            }
        });
        return files;
    }
}