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src/com/google/gson/annotations/Expose.java

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+/*
+ * 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.google.gson.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 {
+ *   &#64Expose private String firstName;
+ *   &#64Expose(serialize = false) private String lastName;
+ *   &#64Expose (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;
+}