Expose.java

/*
 * Copyright (C) 2008 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.smartandroid.sa.json.annotations;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * An annotation that indicates this member should be exposed for JSON
 * serialization or deserialization.
 * 
 * <p>
 * This annotation has no effect unless you build {@link com.google.gson.Gson}
 * with a {@link com.google.gson.GsonBuilder} and invoke
 * {@link com.google.gson.GsonBuilder#excludeFieldsWithoutExposeAnnotation()}
 * method.
 * </p>
 * 
 * <p>
 * Here is an example of how this annotation is meant to be used:
 * <p>
 * 
 * <pre>
 * public class User {
 *   @Expose private String firstName;
 *   @Expose(serialize = false) private String lastName;
 *   @Expose (serialize = false, deserialize = false) private String emailAddress;
 *   private String password;
 * }
 * </pre>
 * 
 * </p>
 * If you created Gson with {@code new Gson()}, the {@code toJson()} and
 * {@code fromJson()} methods will use the {@code password} field along-with
 * {@code firstName}, {@code lastName}, and {@code emailAddress} for
 * serialization and deserialization. However, if you created Gson with
 * {@code Gson gson = new GsonBuilder().excludeFieldsWithoutExposeAnnotation().create()}
 * then the {@code toJson()} and {@code fromJson()} methods of Gson will exclude
 * the {@code password} field. This is because the {@code password} field is not
 * marked with the {@code @Expose} annotation. Gson will also exclude
 * {@code lastName} and {@code emailAddress} from serialization since
 * {@code serialize} is set to {@code false}. Similarly, Gson will exclude
 * {@code emailAddress} from deserialization since {@code deserialize} is set to
 * false.
 * 
 * <p>
 * Note that another way to achieve the same effect would have been to just mark
 * the {@code password} field as {@code transient}, and Gson would have excluded
 * it even with default settings. The {@code @Expose} annotation is useful in a
 * style of programming where you want to explicitly specify all fields that
 * should get considered for serialization or deserialization.
 * 
 * @author Inderjeet Singh
 * @author Joel Leitch
 */
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface Expose {

	/**
	 * If {@code true}, the field marked with this annotation is written out in
	 * the JSON while serializing. If {@code false}, the field marked with this
	 * annotation is skipped from the serialized output. Defaults to
	 * {@code true}.
	 * 
	 * @since 1.4
	 */
	public boolean serialize() default true;

	/**
	 * If {@code true}, the field marked with this annotation is deserialized
	 * from the JSON. If {@code false}, the field marked with this annotation is
	 * skipped during deserialization. Defaults to {@code true}.
	 * 
	 * @since 1.4
	 */
	public boolean deserialize() default true;
}