Annotation Type JsonAdapter

public @interface JsonAdapter

An annotation that indicates the Gson TypeAdapter to use with a class or field.

Here is an example of how this annotation is used:

 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.value(user.firstName + " " + user.lastName);
     // implement the write method
   @Override public User read(JsonReader in) throws IOException {
     // implement read: split name into firstName and lastName
     String[] nameParts = in.nextString().split(" ");
     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 {
   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 GsonBuilder. Field annotations take precedence over GsonBuilder-registered type adapters, which in turn take precedence over annotated types.

The class referenced by this annotation must be either a TypeAdapter or a TypeAdapterFactory. Using the factory interface makes it possible to delegate to the enclosing Gson instance.

Inderjeet Singh, Joel Leitch, Jesse Wilson

Required Element Summary
 Class<?> value
          Either a TypeAdapter or TypeAdapterFactory.

Element Detail


public abstract Class<?> value
Either a TypeAdapter or TypeAdapterFactory.

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