Convert GsonBuilder into Kotlin

Question

Does anyone know how to convert this code into kotlin

GsonBuilder builder = new GsonBuilder();
builder.setLenient();
builder.registerTypeAdapter(Date.class, new JsonDeserializer<Date>() {
        @Override
        public Date deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
            if (json.getAsJsonPrimitive().isNumber()) {
                return new Date(json.getAsJsonPrimitive().getAsLong() * 1000);
            } else {
                return null;
            }
        }
    });
return builder.create();

Then, i tried

val builder = GsonBuilder()
builder.setLenient()
builder.registerTypeAdapter(Date::class.java,.........)
return builder.create()

..... i can't figured it out how to convert the code

Answer 1

The code line that you are asking about can be converted to the following Kotlin code:

builder.registerTypeAdapter(Date::class.java, JsonDeserializer<Date> { 
    json, typeOfT, context ->
    if (json.getAsJsonPrimitive().isNumber())
        Date(json.asJsonPrimitive.asLong * 1000) else
        null
})

First, Kotlin supports SAM conversion of lambdas to Java interfaces, but the syntax is different to Java. Then, returns inside lambdas have different meaning to that in Java, and should be replaced with implicit returns or labeled returns.