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
    • 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.