Due to the popularity of the question on how to stop or manipulate explosions without needing a core mod, I decided to tackle/post the following.

 

What I've illustrated here is how to silently replace tnt with custom tnt, with the players being none-the-wiser. This allows you to write a custom tnt that looks/feels just like tnt, but you can override methods and add custom fields/methods/etc, giving you complete manipulation of tnt on your server.

 

Just replace bedrock in the following example with your custom tnt and voila!

 

 

import java.util.List;

import net.minecraft.block.Block;
import net.minecraft.entity.Entity;
import net.minecraft.entity.item.EntityItemFrame;
import net.minecraft.init.Blocks;
import net.minecraft.item.Item;
import net.minecraft.item.ItemBlock;
import net.minecraft.util.AxisAlignedBB;
import net.minecraftforge.common.util.ForgeDirection;
import net.minecraftforge.event.entity.player.PlayerInteractEvent;

import cpw.mods.fml.common.eventhandler.SubscribeEvent;

public class BuildEventHook {	

@SubscribeEvent
public void onClick(PlayerInteractEvent event) {		

	if (event.action == event.action.RIGHT_CLICK_BLOCK) {			

		if(event.entityPlayer.inventory.mainInventory[event.entityPlayer.inventory.currentItem].getItem() == Item.getItemFromBlock(Blocks.tnt)){
			int i = event.face;
			int x = event.x;
			int y = event.y;
			int z = event.z;
			boolean can = false;

			// bottom top north south west east
			if(i == 0){
				y--;
			}
			else if(i == 1){
				y++;
			}
			else if(i == 2){
				z--;
			}
			else if(i == 3){
				z++;
			}
			else if(i == 4){
				x--;
			}
			else if(i == 5){
				x++;
			}

			if(event.world.isAirBlock(x, y, z))
				can = true;

			List l = event.world.getEntitiesWithinAABB(
					Entity.class,
					AxisAlignedBB.getBoundingBox(
							(double) x,
							(double) y,
							(double) z,
							(double) x + 1.0d,
							(double) y + 1.0d,
							(double) z + 1.0d));
			if(l.size() > 0)
				can = false;

			if(can){
				event.world.setBlock(x, y, z, Blocks.bedrock);					
			}
			event.setCanceled(true);
		}
	}

}	

}

Note: to use a clone of vanilla tnt, you will have to create and register a new entity for the tnt, which can be cloned from EntityTNTPrimed (notice it extends the vanilla):

 

 

public class NewTNTPrimed extends EntityTNTPrimed
{
    /** How long the fuse is */
    public int fuse;
    private EntityLivingBase tntPlacedBy;
    
    public NewTNTPrimed(World p_i1729_1_)
    {
        super(p_i1729_1_);
        this.preventEntitySpawning = true;
        this.setSize(0.98F, 0.98F);
        this.yOffset = this.height / 2.0F;
        this.fuse = 80;
        
    }

    public NewTNTPrimed(World p_i1730_1_, double p_i1730_2_, double p_i1730_4_, double p_i1730_6_, EntityLivingBase p_i1730_8_)
    {
        this(p_i1730_1_);
        this.setPosition(p_i1730_2_, p_i1730_4_, p_i1730_6_);
        float f = (float)(Math.random() * Math.PI * 2.0D);
        this.motionX = (double)(-((float)Math.sin((double)f)) * 0.02F);
        this.motionY = 0.20000000298023224D;
        this.motionZ = (double)(-((float)Math.cos((double)f)) * 0.02F);
        this.fuse = 80;
        this.prevPosX = p_i1730_2_;
        this.prevPosY = p_i1730_4_;
        this.prevPosZ = p_i1730_6_;
        this.tntPlacedBy = p_i1730_8_;
    }

    protected void entityInit() {}

    /**
     * returns if this entity triggers Block.onEntityWalking on the blocks they walk on. used for spiders and wolves to
     * prevent them from trampling crops
     */
    protected boolean canTriggerWalking()
    {
        return false;
    }

    /**
     * Returns true if other Entities should be prevented from moving through this Entity.
     */
    public boolean canBeCollidedWith()
    {
        return !this.isDead;
    }

    /**
     * Called to update the entity's position/logic.
     */
    public void onUpdate()
    {
        this.prevPosX = this.posX;
        this.prevPosY = this.posY;
        this.prevPosZ = this.posZ;
        this.motionY -= 0.03999999910593033D;
        this.moveEntity(this.motionX, this.motionY, this.motionZ);
        this.motionX *= 0.9800000190734863D;
        this.motionY *= 0.9800000190734863D;
        this.motionZ *= 0.9800000190734863D;

        if (this.onGround)
        {
            this.motionX *= 0.699999988079071D;
            this.motionZ *= 0.699999988079071D;
            this.motionY *= -0.5D;
        }

        if (this.fuse-- <= 0)
        {
            this.setDead();

            if (!this.worldObj.isRemote)
            {
            	if(Events.onTNTExplode(this, (EntityPlayer)this.tntPlacedBy))
            		this.explode();                
            }
        }
        else
        {
            this.worldObj.spawnParticle("smoke", this.posX, this.posY + 0.5D, this.posZ, 0.0D, 0.0D, 0.0D);
        }
    }

    private void explode()
    {
        float f = 4.0F;
        this.worldObj.createExplosion(this, this.posX, this.posY, this.posZ, f, true);
    }

    /**
     * (abstract) Protected helper method to write subclass entity data to NBT.
     */
    protected void writeEntityToNBT(NBTTagCompound p_70014_1_)
    {
        p_70014_1_.setByte("NFuse", (byte)this.fuse);
    }

    /**
     * (abstract) Protected helper method to read subclass entity data from NBT.
     */
    protected void readEntityFromNBT(NBTTagCompound p_70037_1_)
    {
        this.fuse = p_70037_1_.getByte("NFuse");
    }

    @SideOnly(Side.CLIENT)
    public float getShadowSize()
    {
        return 0.0F;
    }

    /**
     * returns null or the entityliving it was placed or ignited by
     */
    public EntityLivingBase getTntPlacedBy()
    {
        return this.tntPlacedBy;
    }
}

 

take note of this line:

if(Events.onTNTExplode(this, (EntityPlayer)this.tntPlacedBy)) this.explode();

 

...it will let you create an explosion event handler as such:

 

	/**
 * Fired just before a tnt explosion
 * @param tnt
 * @param player = null often! be careful!
 * @return false will cancel the explosion
 */
public static boolean onTNTExplode(NewTNTPrimed tnt, EntityPlayer player) {



	return true;
}

 

Also, your tnt may not render correctly after lighting it. Be sure to register the renderer in your proxy! I suggest using the same renderer as vanilla tnt.

 

RenderingRegistry.registerEntityRenderingHandler(NewTNTPrimed.class, new RenderTNTPrimed());

 

Edit: Sorry, be sure to put

if(!event.world.isRemote){

in your PlayerInteractEvent check. The check should actually look as follows.

if(!event.world.isRemote){
			if(event.entityPlayer.inventory.mainInventory[event.entityPlayer.inventory.currentItem].getItem() == Item.getItemFromBlock(Blocks.tnt)){
				int i = event.face;
				int x = event.x;
				int y = event.y;
				int z = event.z;
				boolean can = false;

				// bottom top north south west east
				if(i == 0){
					y--;
				}
				else if(i == 1){
					y++;
				}
				else if(i == 2){
					z--;
				}
				else if(i == 3){
					z++;
				}
				else if(i == 4){
					x--;
				}
				else if(i == 5){
					x++;
				}

				if(event.world.isAirBlock(x, y, z))
					can = true;

				List l = event.world.getEntitiesWithinAABB(
						Entity.class,
						AxisAlignedBB.getBoundingBox(
								(double) x,
								(double) y,
								(double) z,
								(double) x + 1.0d,
								(double) y + 1.0d,
								(double) z + 1.0d));
				if(l.size() > 0)
					can = false;

				if(can){
					event.world.setBlock(x, y, z, IFaction.NewTNT);		
					event.world.notifyBlockOfNeighborChange(x, y, z, IFaction.NewTNT);
				}
				event.setCanceled(true);
			}