Annotation Type JsonAdapter

@Retention(CLASS) @Target({TYPE,FIELD}) public @interface JsonAdapter

Hands a type's JSON form to the application's own JsonTypeAdapter.

On a field it applies to that field; on a class, to every field, element and body of that class, which is how a type the generated codecs cannot map -- a money value, an identifier wrapper -- gets one form everywhere. A field's adapter wins over its class's.

public final class EpochSecondsAdapter implements JsonTypeAdapter<java.util.Date> {
    public Object toJson(java.util.Date d) {
        return d == null ? null : Long.valueOf(d.getTime() / 1000);
    }
    public java.util.Date fromJson(Object json) {
        if (json == null) {
            return null;
        }
        // instanceof, never a bare cast: a failed cast does not throw on iOS.
        if (!(json instanceof Number)) {
            throw new IllegalArgumentException("expected epoch seconds");
        }
        return new java.util.Date(((Number) json).longValue() * 1000);
    }
}

@Mapped
public class Invoice {
    @JsonAdapter(EpochSecondsAdapter.class)
    public java.util.Date issued;
}

The adapter needs a public constructor without arguments. The generated code creates one instance per adapter class and calls it directly, so nothing is found by name at run time and the translated binary keeps the class.

  • Required Element Summary

    Required Elements
    Modifier and Type
    Required Element
    Description
    Class<? extends JsonTypeAdapter>
    value
    The adapter class.