Loot Tables

Custom_Chest_Loot.json

  "pools":[
   {

   "name": "main",
   "rolls": 3,
   "entries": [

      {
      "type": "item",
      "name": "minecraft:porkchop",
      "weight": 20,
      },
      {
      "type": "item",
      "name": "augmentedvoid:legendbow",
      "weight": 10,
      }

   ]
 }
]

ItemLegendaryGem

package mod.teamvoid.augmentedvoid.items;

import java.util.List;
import java.util.Random;

import mod.teamvoid.augmentedvoid.init.ModLootTables;
import mod.teamvoid.augmentedvoid.init.SpaceTabs;
import net.minecraft.block.state.IBlockState;
import net.minecraft.creativetab.CreativeTabs;
import net.minecraft.entity.player.EntityPlayer;
import net.minecraft.init.Blocks;
import net.minecraft.item.Item;
import net.minecraft.item.ItemStack;
import net.minecraft.tileentity.TileEntity;
import net.minecraft.tileentity.TileEntityChest;
import net.minecraft.util.EnumActionResult;
import net.minecraft.util.EnumFacing;
import net.minecraft.util.EnumHand;
import net.minecraft.util.ResourceLocation;
import net.minecraft.util.math.BlockPos;
import net.minecraft.util.text.TextFormatting;
import net.minecraft.world.World;
import net.minecraft.world.storage.loot.LootTableList;

public class ItemLegendaryGem extends Item{

	
	public ItemLegendaryGem(){
		super();
		this.setRegistryName("legendarygem");
		this.setUnlocalizedName("legendarygem");
		setCreativeTab(SpaceTabs.tabSpace);
    
    }
	
	public void addInformation(ItemStack stack, EntityPlayer player, List list, boolean par4)
    {
    	list.add(TextFormatting.WHITE + "Creates a chest with loot");
    	list.add(TextFormatting.ITALIC + "Normally places our custom loot table");
    	list.add(TextFormatting.ITALIC + "Sneaking places a modified loot table");
    }
	
	public EnumActionResult onItemUse(ItemStack stack, EntityPlayer player, World world, BlockPos pos, EnumHand hand, EnumFacing theface, float hitX, float hitY, float hitZ)
	{
		
		IBlockState iblockstate = Blocks.CHEST.getDefaultState();
		world.setBlockState(pos, Blocks.CHEST.correctFacing(world, pos, iblockstate), 2);
        TileEntity tileentity = world.getTileEntity(pos);
        
        Random random = new Random();

        if (tileentity instanceof TileEntityChest)   
        {
        	/**Our Custom Loot**/
        	ResourceLocation location = ModLootTables.Custom_Chest_Loot;
        	
        	if(player.isSneaking()){
        		/**Our modified Spawn Chest Loot**/
        		location = LootTableList.CHESTS_SPAWN_BONUS_CHEST;
        	}        	
        	
            ((TileEntityChest)tileentity).setLootTable(location, random.nextLong());
        }
		
		
		return EnumActionResult.SUCCESS;
	}
	
}

ModEventHandler

package mod.teamvoid.augmentedvoid.init;

import java.util.List;

import net.minecraft.util.ResourceLocation;
import net.minecraft.world.storage.loot.LootEntry;
import net.minecraft.world.storage.loot.LootEntryTable;
import net.minecraft.world.storage.loot.LootPool;
import net.minecraft.world.storage.loot.LootTable;
import net.minecraft.world.storage.loot.RandomValueRange;
import net.minecraft.world.storage.loot.conditions.LootCondition;
import net.minecraftforge.event.LootTableLoadEvent;
import net.minecraftforge.fml.common.eventhandler.SubscribeEvent;
import net.minecraftforge.fml.relauncher.ReflectionHelper;

public class ModEventHandler { 
		
	@SubscribeEvent
	public void Table_Additives(LootTableLoadEvent event){		
		
		/*Name of the table*/
		String name = event.getName().toString();
		
		try{
			
			/*Loot tables to match*/
			if(name.matches("minecraft:chests/spawn_bonus_chest") 	
				  || name.matches("minecraft:entities/chicken")){

				
				
				/*Adding a loot pool to the target table*/
				event.getTable().addPool(getAdditive("augmentedinferno:Loot_Additive"));
			}
			
			/*Finding and adding to non mincraft loot*/
			if(name.matches("augmentedvoid:Custom_Chest_Loot")){				
				
			}
			
					//setblock ~ ~ ~ minecraft:chest 2 replace {LootTable:chests/spawn_bonus_chest}
		}
		catch(Exception exc){
		}
		
	}
	
	/** Here we are creating a new pool from the resource location we feed it. **/
	private LootPool getAdditive(String entryName) {
		return new LootPool(new LootEntry[] { getAdditiveEntry(entryName, 1) }, new LootCondition[0], new RandomValueRange(1), new RandomValueRange(0, 1), "Additive_pool");
	}

	/** Make sure to setup your resource location accordingly **/
	private LootEntryTable getAdditiveEntry(String name, int weight) {
		return new LootEntryTable(new ResourceLocation(name), weight, 0, new LootCondition[0], "Additive_entry");
	}

	
}

ModLootTables

package mod.teamvoid.augmentedvoid.init;

import mod.teamvoid.augmentedvoid.Main;
import mod.teamvoid.augmentedvoid.Reference;
import net.minecraft.util.ResourceLocation;
import net.minecraft.world.storage.loot.LootTable;
import net.minecraft.world.storage.loot.LootTableList;


/** Registration and reference for new loot tables **/
public class ModLootTables {
	
	public static final ResourceLocation Custom_Chest_Loot = register("Custom_Chest_Loot");

	
	private static ResourceLocation register(String id) {
		return LootTableList.register(new ResourceLocation(Reference.MOD_ID, id));
	}
}