The complete code for getting an dex file from .class files and then generating a java.lang.Class object

JavaCommonFileSetup.java

package com.exsent.app.example;

import android.content.Context;

import java.io.File;
import java.io.IOException;
import java.util.Arrays;
import java.util.List;
import java.util.Objects;

import dalvik.system.DexClassLoader;

/**
 * Created by Jim-Linus Valentin Ahrend on 2/3/21.
 *
 * This is a part of the exsent source code.
 *
 **/
class JavaCommonFileSetup {

    private static final String TAG = JavaCommonFileSetup.class.getSimpleName();

    public interface ClassPro {
        void classLoaded(Class c);
    }

    static void jarToClass(final Context context, File jar_file, ClassPro pro) {

        final String DEX_FILE_NAME = "YourDexFile";
        final String DIR_NAME = "YourDirName";

        Thread thread = new Thread(() -> {

            try {



                File storage = new File(DIR_NAME);

                //check space


        /*
        Android.jar is always the same, a international file dir is needed!
         */

                java.util.jar.JarFile jar = new java.util.jar.JarFile(jar_file);
                java.util.Enumeration enumEntries = jar.entries();
                while (enumEntries.hasMoreElements()) {
                    java.util.jar.JarEntry file = (java.util.jar.JarEntry) enumEntries.nextElement();
                    java.io.File f = new java.io.File(storage.getAbsolutePath() + "/" + file.getName());
                    if (!f.getAbsolutePath().contains("__MACOSX")) {

                        if (file.isDirectory()) { // if its a directory, create it
                            //noinspection ResultOfMethodCallIgnored
                            f.mkdir();
                            continue;
                        }
                        java.io.InputStream is = jar.getInputStream(file); // get the input stream
                        java.io.FileOutputStream fos = new java.io.FileOutputStream(f);
                        while (is.available() > 0) {  // write contents of 'is' to 'fos'
                            fos.write(is.read());
                        }
                        fos.close();
                        is.close();
                    }
                }
                jar.close();


                //generating file with code


                //generated successfully


                List<File> files2 = Arrays.asList(Objects.requireNonNull(storage.listFiles(pathname -> pathname.getAbsolutePath().endsWith(".class"))));

                files2.forEach(file -> {
                    if (file.isDirectory()) {
                        List<File> add_files = Arrays.asList(Objects.requireNonNull(file.listFiles(pathname -> pathname.getAbsolutePath().endsWith(".class"))));
                        files2.addAll(add_files);
                    }
                });

                String[] args2 = new String[5 + files2.size()];
                args2[0] = "--dex";
                args2[1] = "--keep-classes";
                args2[2] = "--output=" + DEX_FILE_NAME + ".dex";
                args2[3] = "--min-sdk-version=26";
                args2[4] = "--verbose";
                int var0 = 5;
                for (File f :
                        files2) {
                    args2[var0] = f.getAbsolutePath();
                    var0++;
                }

                com.android.dx.command.Main.main(args2, () -> {

                    //noinspection ResultOfMethodCallIgnored
                    jar_file.delete();

                    DexClassLoader cl = new DexClassLoader(storage.getAbsolutePath() + "/" + DEX_FILE_NAME + ".dex", storage.getAbsolutePath(), null, context.getClassLoader());
                    try {
                        pro.classLoaded(cl.loadClass("YOUR_PACKAGE.YOUR_CLASS"));
                    } catch (Exception e) {
                        e.printStackTrace();
                        pro.classLoaded(null);
                    }
                });
            }catch (IOException ioe){
                ioe.printStackTrace();
            }
        });
        thread.start();
    }

}