Annotation Type JsonAdapter

@Retention(RUNTIME) @Target({TYPE,FIELD}) 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:

@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 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, or must implement one or both of JsonDeserializer or JsonSerializer. Using TypeAdapterFactory makes it possible to delegate to the enclosing Gson instance.

Since:
2.3
Author:
Inderjeet Singh, Joel Leitch, Jesse Wilson

  • Required Element Summary

    Required Elements
    Modifier and Type
    Required Element
    Description
    Class<?>
    value
    Either a TypeAdapter or TypeAdapterFactory, or one or both of JsonDeserializer or JsonSerializer.

  • Optional Element Summary

    Optional Elements
    Modifier and Type
    Optional Element
    Description
    boolean
    nullSafe
    false, to be able to handle null values within the adapter, default value is true.