Deserializing Option returns None instead of an exception in json4s

Question

When running the following code I would expect an exception, but I get None instead. Is that expected?

import org.json4s.jackson.JsonMethods
import org.json4s.{DefaultFormats, Formats}
implicit val f: Formats = DefaultFormats
val json ="{ \"a\" : { \"c\": 1 }}"

case class Foo(a: Option[String])
val foo = JsonMethods.parse(json).extract[Foo]

println(foo)

>  Foo(None)

also that code:

import org.json4s.jackson.JsonMethods
import org.json4s.{DefaultFormats, Formats}
implicit val f: Formats = DefaultFormats
val json ="{ \"a\" : { \"c\": 1 }}"

case class Foo(a: String = "")
val foo = JsonMethods.parse(json).extract[Foo]

println(foo)

>  Foo()

Well, I would argue that the idea of **Option** is it shouldn't fail. If it couldn't read `a` as a **String** then it will return **None**. — Luis Miguel Mejía Suárez, Feb 25 '20 at 18:53
Well, you got a point. It depends on how strict you want it to be. Probably there are ways to configure it. — Luis Miguel Mejía Suárez, Feb 25 '20 at 19:07
BEWARE: Json4s is [vulnerable under DoS/DoW attacks](https://github.com/json4s/json4s/issues?utf8=%E2%9C%93&q=is%3Aissue+is%3Aopen+denial)! — Andriy Plokhotnyuk, May 06 '20 at 05:49

score 4 · Accepted Answer · answered Feb 25 '20 at 19:15

You can enforce strict option parsing by changing the default format as such:

implicit val f: Formats = DefaultFormats.withStrictOptionParsing

The underlying exception:

[error] (run-main-2) org.json4s.package$MappingException: No usable value for a
[error] Do not know how to convert JObject(List((c,JInt(1)))) into class java.lang.String

Deserializing Option returns None instead of an exception in json4s

1 Answers1