Using Google Guava to restore blocks after a certain amount of time.

TemporaryModifcations.java

package com.comphenix.example;

import java.lang.ref.WeakReference;
import java.util.concurrent.TimeUnit;

import org.bukkit.World;
import org.bukkit.block.Block;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;

import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.block.BlockBreakEvent;
import org.bukkit.plugin.PluginManager;
import org.bukkit.plugin.java.JavaPlugin;
import org.bukkit.util.BlockVector;

import com.google.common.cache.Cache;
import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.RemovalListener;
import com.google.common.cache.RemovalNotification;

public class TemporaryModifcations extends JavaPlugin implements Listener {

    public static int TICKS_PER_SECOND = 20;
    
    private static class BlockData {
        private WeakReference<World> worldReference;
        private int typeID;
        private byte data;
        
        public BlockData(Block block) {
            this.worldReference = new WeakReference<World>(block.getWorld());
            this.typeID = block.getTypeId();
            this.data = block.getData();
        }
        
        /**
         * Restore the current block.
         * @return TRUE if the block was restored, FALSE otherwise.
         */
        public boolean restore(BlockVector vector) {
            if (getWorld() != null) {
                Block block = getWorld().getBlockAt(vector.toLocation(getWorld()));
                
                // Restore type and data
                block.setTypeId(typeID);
                block.setData(data);
                return true;
            } else {
                return false;
            }
        }
        
        public World getWorld() {
            return worldReference.get();
        }
    }
    
    private Cache<BlockVector, BlockData> restoreQueue;
    
    @Override
    public void onLoad() {
        restoreQueue = CacheBuilder.
            newBuilder().
            concurrencyLevel(2).
            weakValues().
            expireAfterWrite(10, TimeUnit.SECONDS).
            removalListener(new RemovalListener<BlockVector, BlockData>() {
                @Override
                public void onRemoval(RemovalNotification<BlockVector, BlockData> entry) {
                    entry.getValue().restore(entry.getKey());
                }
            }).
            build(new CacheLoader<BlockVector, BlockData>() {
                @Override
                public BlockData load(BlockVector arg0) throws Exception {
                    throw new RuntimeException("Unsupported! Cannot generate entries, must be placed manually.");
                }
            });
    }
    
    @Override
    public void onEnable() {
        PluginManager manager = getServer().getPluginManager();
        manager.registerEvents(this, this);
        
        // Run the block cleanup once per second
        getServer().getScheduler().scheduleSyncRepeatingTask(this, new Runnable() {
            @Override
            public void run() {
                restoreQueue.cleanUp();
            }
        }, TICKS_PER_SECOND, TICKS_PER_SECOND);
    }
    
    @EventHandler
    public void onBlockBreakEvent(BlockBreakEvent event) {
        BlockData data = new BlockData(event.getBlock());
        BlockVector vector = new BlockVector(event.getBlock().getLocation().toVector());
        
        // Expire after two minutes
        restoreQueue.asMap().put(vector, data);
    }
}