@Retention(value=RUNTIME)
@Target(value={TYPE,FIELD})
public @interface JsonAdapter
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.
| Modifier and Type | Required Element and Description |
|---|---|
java.lang.Class<?> |
value
|
| Modifier and Type | Optional Element and Description |
|---|---|
boolean |
nullSafe
false, to be able to handle
null values within the adapter, default value is true. |
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