FinalFieldHelper.java

/*
 * Minecraft Forge
 * Copyright (c) 2016.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation version 2.1
 * of the License.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 */

package net.minecraftforge.fml.common.registry;

import com.google.common.base.Throwables;

import javax.annotation.Nullable;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;

/**
 * Helper class for setting final fields.
 */
class FinalFieldHelper
{
    private static Field modifiersField;
    private static Object reflectionFactory;
    private static Method newFieldAccessor;
    private static Method fieldAccessorSet;
    static Field makeWritable(Field f) throws Exception
    {
        if (modifiersField == null)
        {
            Method getReflectionFactory = Class.forName("sun.reflect.ReflectionFactory").getDeclaredMethod("getReflectionFactory");
            reflectionFactory = getReflectionFactory.invoke(null);
            newFieldAccessor = Class.forName("sun.reflect.ReflectionFactory").getDeclaredMethod("newFieldAccessor", Field.class, boolean.class);
            fieldAccessorSet = Class.forName("sun.reflect.FieldAccessor").getDeclaredMethod("set", Object.class, Object.class);
            modifiersField = Field.class.getDeclaredField("modifiers");
            modifiersField.setAccessible(true);
        }
        modifiersField.setInt(f, f.getModifiers() & ~Modifier.FINAL);
        return f;
    }


    static void setField(Field field, @Nullable Object instance, Object thing) throws Exception
    {
        Object fieldAccessor = newFieldAccessor.invoke(reflectionFactory, field, false);
        fieldAccessorSet.invoke(fieldAccessor, instance, thing);
    }
}