AHPlayer.java

package me.tmp.test;

import lombok.Getter;
import org.bukkit.Bukkit;
import org.bukkit.entity.Player;

import java.util.LinkedList;
import java.util.List;
import java.util.UUID;

/**
 * Created by TheMasteredPanda on 18/01/2017.
 */

public class AHPlayer
{
    private @Getter UUID playerUUID;
    private @Getter LinkedList<Listing> listings;
    private @Getter List<UUID> watchedAuctioneers;
    private @Getter long totalProfitMade;
    private @Getter int itemsSold;
    private @Getter int itemsBrought;
    private @Getter int rating;
    private Player player;

    protected AHPlayer(UUID playerUUID, LinkedList<Listing> listings, List<UUID> watchedAuctioneers, List<Listing> watchedItems, long totalProfitMade, int itemsSold, int itemsBrought, boolean blackListed)
    {
        this.playerUUID = playerUUID;
        this.listings = listings;
        this.watchedAuctioneers = watchedAuctioneers;
        this.totalProfitMade = totalProfitMade;
        this.itemsSold = itemsSold;
        this.itemsBrought = itemsBrought;
        this.rating = rating;
        this.player = Bukkit.getPlayer(playerUUID);
    }
}

CommandGive.java

package me.tmp.test;

import org.bukkit.Bukkit;
import org.bukkit.command.Command;
import org.bukkit.command.CommandExecutor;
import org.bukkit.command.CommandSender;

/**
 * Created by TheMasteredPanda on 22/01/2017.
 */

public class CommandGive implements CommandExecutor
{
    private JsonTest instance = JsonTest.getInstance();
    public boolean onCommand(CommandSender commandSender, Command command, String s, String[] strings)
    {
        if (command.getName().equalsIgnoreCase("givelistingitems")) {
            for (int i = 0; i < this.instance.listings.size(); i++) {
                Listing listing = this.instance.listings.get(i);
                Bukkit.getPlayer(commandSender.getName()).getInventory().addItem(listing.getItem());
                commandSender.sendMessage("Added Item "+ listing.getItem());
            }
        }
        return true;
    }
}

JsonTest.java

package me.tmp.test;

import com.google.common.collect.Lists;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import lombok.Getter;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.player.PlayerJoinEvent;
import org.bukkit.plugin.java.JavaPlugin;

import java.io.*;
import java.util.List;
import java.util.UUID;

/**
 * Created by TheMasteredPanda on 21/01/2017.
 */

public class JsonTest extends JavaPlugin implements Listener
{
    private static @Getter JsonTest instance;
    private Gson gson = new GsonBuilder().setPrettyPrinting().create();
    public List<Listing> listings = Lists.newArrayList();
    private AHPlayer player;

    @Override
    public void onLoad()
    {
        instance = this;

        try  {
            getCommand("givelistingitems").setExecutor(new CommandGive());
        } catch (NullPointerException npe) {
            npe.printStackTrace();
        }
    }

    @Override
    public void onEnable()
    {
        File[] files = new File(this.getDataFolder(), "JsonTest").listFiles();

        if (files != null) {
            for (int i = 0; i < files.length; i++) {
                try {
                    listings.add(gson.fromJson(new FileReader(files[i]), Listing.class));
                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    @EventHandler
    public void onPlayerJoin(PlayerJoinEvent e)
    {
        this.player = new AHPlayer(e.getPlayer().getUniqueId(), Lists.newLinkedList(listings), Lists.newArrayList(new UUID[]{UUID.randomUUID(), UUID.randomUUID(), UUID.randomUUID()}), listings, 10000L, 20, 10, false);

        File f = new File(this.getDataFolder(), this.player.getPlayerUUID() + ".json");

        if (!f.exists()) {
            try {
                f.createNewFile();
                FileWriter writer = new FileWriter(f);
                writer.write(gson.toJson(this.player));
                writer.close();
            } catch (IOException ioe) {
                ioe.printStackTrace();
            }
        }
    }
}

Listing.java

package me.tmp.test;

import lombok.Getter;
import lombok.Setter;
import org.bukkit.inventory.ItemStack;

import java.util.UUID;

/**
 * Created by TheMasteredPanda on 22/01/2017.
 */

public class Listing
{
    private @Getter
    int listingID;
    private @Getter UUID auctioneer;
    private @Getter @Setter
    UUID highestCurrentBidder;
    private @Getter long startPrice;
    private @Getter @Setter long currentPrice;
    private @Getter long lowestPossibleBid;
    private @Getter
    ItemStack item;
    private @Getter float listingDuration;
    private @Getter boolean expired;

    public Listing(int listingID, ItemStack item, UUID auctioneer, UUID highestCurrentBidder, long startPrice, long currentPrice, long lowestPossibleBid, float listingDuration, boolean expired)
    {
        this.listingID = listingID;
        this.auctioneer = auctioneer;
        this.startPrice = startPrice;
        this.currentPrice = currentPrice;
        this.lowestPossibleBid = lowestPossibleBid;
        this.listingDuration = listingDuration;
        this.expired = expired;
        this.item = item;
    }
}