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, 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

Required Element Summary

Required Elements

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

Element Detail

value

public abstract java.lang.Class<?> value

Either a TypeAdapter or TypeAdapterFactory, or one or both of JsonDeserializer or JsonSerializer.

nullSafe

public abstract boolean nullSafe

false, to be able to handle null values within the adapter, default value is true.

Default:

true