java/src/main/com/google/appengine/api/datastore/PreGet.java

   1 // Copyright 2012 Google Inc. All Rights Reserved.
   2
   3 package com.google.appengine.api.datastore;
   4
   5 import java.lang.annotation.ElementType;
   6 import java.lang.annotation.Retention;
   7 import java.lang.annotation.RetentionPolicy;
   8 import java.lang.annotation.Target;
   9
  10 /**
  11  * Identifies a callback method to be invoked before an {@link Entity} of any
  12  * of the specified kinds is fetched from the datastore via a get() rpc.  If
  13  * {@link #kinds()} is not provided the callback will execute for all kinds.
  14  * Methods with this annotation must return {@code void}, must accept a single
  15  * argument of type {@link PreGetContext}, must not throw any checked
  16  * exceptions, must not be static, and must belong to a class with a no-arg
  17  * constructor.  Neither the method nor the no-arg constructor of the class to
  18  * which it belongs are required to be public.  Methods with this annotation
  19  * are free to throw any unchecked exception they like.  Throwing an unchecked
  20  * exception will prevent callbacks that have not yet been executed from
  21  * running, and the exception will propagate to the code that invoked the
  22  * datastore operation that resulted in the invocation of the callback.
  23  * Throwing an unchecked exception from a callback will prevent the datastore
  24  * operation from executing.
  25  *
  26  */
  27 @Target(ElementType.METHOD)
  28 @Retention(RetentionPolicy.RUNTIME)
  29 public @interface PreGet {
  30
  31   /**
  32    * The kinds to which this callback applies.  The default value is an empty
  33    * array, which indicates that the callback should run for all kinds.
  34    *
  35    * @return The kinds to which this callback applies.
  36    */
  37   String[] kinds() default {};
  38 }