add new class

src/main/java/net/minecraftforge/common/util/EntitySnapshot.java

@@ -0,0 +1,27 @@
+package net.minecraftforge.common.util;
+
+import org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason;
+import net.minecraft.entity.Entity;
+import net.minecraft.world.World;
+
+public class EntitySnapshot{
+
+    public final World mWorld;
+    public final Entity mEntity;
+    public final SpawnReason mReason;
+
+    public EntitySnapshot(World pWorld,Entity pEntity,SpawnReason pReason){
+        this.mWorld=pWorld;
+        this.mEntity=pEntity;
+        this.mReason=pReason==null?SpawnReason.CUSTOM:pReason;
+    }
+
+    public boolean apply(){
+        return this.mWorld.addEntity(this.mEntity,this.mReason);
+    }
+
+    public void cancel(){
+        this.mEntity.setDead();
+        this.mWorld.removeEntity(this.mEntity);
+    }
+}