Use built-in java bytecode generation

MethodAccessorsGenerator.java

package ru.narod.dimzon541.utils.reflect;

import sun.reflect.ConstructorAccessor;
import sun.reflect.FieldAccessor;
import sun.reflect.MethodAccessor;

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

@SuppressWarnings("UnusedDeclaration")
public class MethodAccessorsGenerator {
    private static final Object generatorObject;
    private static final MethodAccessor generateMethod;
    private static final MethodAccessor generateConstructor;
    private static final MethodAccessor newFieldAccessor;

    static {
        try {
            Class<?> aClass = Class.forName("sun.reflect.MethodAccessorGenerator");
            Constructor<?>[] declaredConstructors = aClass.getDeclaredConstructors();
            Constructor<?> declaredConstructor = declaredConstructors[0];
            declaredConstructor.setAccessible(true);
            generatorObject = declaredConstructor.newInstance();
            Method bar = aClass.getMethod("generateMethod", Class.class, String.class, Class[].class, Class.class, Class[].class, Integer.TYPE);
            bar.setAccessible(true);
            generateMethod = (MethodAccessor) bar.invoke(
                    generatorObject,
                    bar.getDeclaringClass(),
                    bar.getName(),
                    bar.getParameterTypes(),
                    bar.getReturnType(),
                    bar.getExceptionTypes(),
                    bar.getModifiers());
            bar = aClass.getMethod("generateConstructor", Class.class, Class[].class, Class[].class, Integer.TYPE);
            generateConstructor = newMethodAccessor(bar);
            aClass = Class.forName("sun.reflect.UnsafeFieldAccessorFactory");
            bar = aClass.getDeclaredMethod("newFieldAccessor", Field.class, Boolean.TYPE);
            newFieldAccessor = newMethodAccessor(bar);
        } catch (NoSuchMethodException
                | InstantiationException
                | IllegalAccessException
                | InvocationTargetException
                | ClassNotFoundException e) {
            throw new RuntimeException(e);
        }
    }
    public static FieldAccessor newFieldAccessor(Field field, boolean overrideFinalCheck){
        try {
            return (FieldAccessor) newFieldAccessor.invoke(null,new Object[]{field,overrideFinalCheck});
        } catch (InvocationTargetException e) {
            throw new RuntimeException(e);
        }
    }
    public static  MethodAccessor newMethodAccessor(Method bar){
        try {
            return  (MethodAccessor) generateMethod.invoke(
                    generatorObject, new Object[]{
                    bar.getDeclaringClass(),
                    bar.getName(),
                    bar.getParameterTypes(),
                    bar.getReturnType(),
                    bar.getExceptionTypes(),
                    bar.getModifiers()});
        } catch (InvocationTargetException e) {
            throw new RuntimeException(e);
        }
    }
    public static ConstructorAccessor newConstructorAccessor(Constructor<?> bar){
        try {
            return  (ConstructorAccessor) generateConstructor.invoke(
                    generatorObject, new Object[]{
                    bar.getDeclaringClass(),
                    bar.getParameterTypes(),
                    bar.getExceptionTypes(),
                    bar.getModifiers()});
        } catch (InvocationTargetException e) {
            throw new RuntimeException(e);
        }
    }
}