com.google.gson.annotations.JsonAdapter Maven / Gradle / Ivy
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/*
* Copyright (C) 2014 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 com.google.gson.JsonDeserializer;
import com.google.gson.JsonSerializer;
import com.google.gson.TypeAdapter;
import com.google.gson.TypeAdapterFactory;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* An annotation that indicates the Gson {@link TypeAdapter} to use with a class
* or field.
*
* Here is an example of how this annotation is used:
*
* @JsonAdapter(UserJsonAdapter.class)
* public class User {
* public final String firstName, lastName;
* private User(String firstName, String lastName) {
* this.firstName = firstName;
* this.lastName = lastName;
* }
* }
* public class UserJsonAdapter extends TypeAdapter<User> {
* @Override public void write(JsonWriter out, User user) throws IOException {
* // implement write: combine firstName and lastName into name
* out.beginObject();
* out.name("name");
* out.value(user.firstName + " " + user.lastName);
* out.endObject();
* // implement the write method
* }
* @Override public User read(JsonReader in) throws IOException {
* // implement read: split name into firstName and lastName
* in.beginObject();
* in.nextName();
* String[] nameParts = in.nextString().split(" ");
* in.endObject();
* return new User(nameParts[0], nameParts[1]);
* }
* }
*
*
* Since User class specified UserJsonAdapter.class in @JsonAdapter annotation, it
* will automatically be invoked to serialize/deserialize User instances.
*
* Here is an example of how to apply this annotation to a field.
*
* private static final class Gadget {
* @JsonAdapter(UserJsonAdapter2.class)
* final User user;
* Gadget(User user) {
* this.user = user;
* }
* }
*
*
* It's possible to specify different type adapters on a field, that
* field's type, and in the {@link com.google.gson.GsonBuilder}. Field
* annotations take precedence over {@code GsonBuilder}-registered type
* adapters, which in turn take precedence over annotated types.
*
* The class referenced by this annotation must be either a {@link
* TypeAdapter} or a {@link TypeAdapterFactory}, or must implement one
* or both of {@link JsonDeserializer} or {@link JsonSerializer}.
* Using {@link TypeAdapterFactory} makes it possible to delegate
* to the enclosing {@code Gson} instance.
*
* @since 2.3
*
* @author Inderjeet Singh
* @author Joel Leitch
* @author Jesse Wilson
*/
// Note that the above example is taken from AdaptAnnotationTest.
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE, ElementType.FIELD})
public @interface JsonAdapter {
/** Either a {@link TypeAdapter} or {@link TypeAdapterFactory}, or one or both of {@link JsonDeserializer} or {@link JsonSerializer}. */
Class value();
/** false, to be able to handle {@code null} values within the adapter, default value is true. */
boolean nullSafe() default true;
}