Added EntityPersistor

EntityPersistor allows you to wrap an Entity instance with a proxy which will try to ensure persistence of the object as a valid reference

src/redempt/redlib/misc/EntityPersistor.java

@@ -0,0 +1,67 @@
+package redempt.redlib.misc;
+
+import org.bukkit.Bukkit;
+import org.bukkit.entity.Entity;
+
+import java.lang.reflect.InvocationHandler;
+import java.lang.reflect.Method;
+import java.lang.reflect.Proxy;
+
+/**
+ * An Entity in Spigot may not persist if the entity it refers to is unloaded, then loaded again at a later time.
+ * This can make development very annoying, as you have to constantly check whether the Entity is still valid or not.
+ * EntityPersistor wraps an Entity using a proxy, and anytime a method is called on the Entity, it will check if
+ * the Entity instance is still valid. If it isn't, it will attempt to replace it with a valid instance by re-fetching
+ * the Entity from Bukkit.
+ */
+public class EntityPersistor {
+
+	/**
+	 * Wraps an Entity object with a proxy which will attempt to ensure the Entity object remains valid
+	 * even if the entity's chunk is unloaded, then loaded again. Helpful if you need a reference to an
+	 * Entity over a long period of time which must not be broken. Note that any wrapped Entity will not
+	 * interact with {@link Object#equals(Object)} reflexively. You must call .equals() on the Entity
+	 * which has been wrapped, not on another Entity comparing it to this one. This could not be avoided,
+	 * unfortunately, but as long as you are aware of that, it should work fine.
+	 * @param entity The Entity to wrap
+	 * @param <T> The type of the Entity
+	 * @return The wrapped Entity
+	 */
+	public static <T extends Entity> T persist(T entity) {
+		Class<?> clazz = entity.getClass();
+		boolean foundInterface = false;
+		for (Class<?> iface : clazz.getInterfaces()) {
+			if (Entity.class.isAssignableFrom(iface)) {
+				clazz = iface;
+				foundInterface = true;
+				break;
+			}
+		}
+		if (!foundInterface) {
+			throw new IllegalArgumentException("The provided object cannot be wrapped!");
+		}
+		return (T) Proxy.newProxyInstance(clazz.getClassLoader(), new Class[]{clazz}, new InvocationHandler() {
+
+			private T instance = entity;
+
+			@Override
+			public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
+				if (!instance.isValid()) {
+					T replace = (T) Bukkit.getEntity(instance.getUniqueId());
+					if (replace != null) {
+						instance = replace;
+					}
+				}
+				if (method.getName().equals("equals") && method.getParameters().length == 1 && method.getParameters()[0].getName().equals("Object")) {
+					if (args[0] instanceof Entity) {
+						return ((Entity) args[0]).getUniqueId().equals(instance.getUniqueId());
+					}
+					return false;
+				}
+				return method.invoke(instance, args);
+			}
+
+		});
+	}
+
+}

src/redempt/redlib/misc/Hologram.java

@@ -253,7 +253,7 @@ private ArmorStand spawn(int line, String text) {
 		} else {
 			loc = start;
 		}
-		ArmorStand stand = (ArmorStand) loc.getWorld().spawnEntity(loc, EntityType.ARMOR_STAND);
+		ArmorStand stand = EntityPersistor.persist((ArmorStand) loc.getWorld().spawnEntity(loc, EntityType.ARMOR_STAND));
 		initiate(stand);
 		stand.setCustomName(text);
 		return stand;