com.google.gson.annotations

Annotation Type JsonAdapter

@Retention(value=RUNTIME)
@Target(value={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. Using the factory interface 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 and Description
Class<?>	value Either a TypeAdapter or TypeAdapterFactory.

Element Detail

value

public abstract Class<?> value

Either a TypeAdapter or TypeAdapterFactory.