Deserializing to Option[T] doesn't properly handle json string values

[c089]

I encountered an issue with deserializing JSON like this:

{"x": "42", "y": "foo"}

Note the value of x is a valid integer, but represented as a JSON string, which is fairly common. Now, trying to deserialize this to Ints works as expected: x will be parsed as Int, and y will trigger an InvalidFormatException. However, if you try to serialize this as Option[Int], it will succeed in both cases, and you get a reference to a Some that holds a String, which caused very subtle bugs in our code.

I wanted to do a pull request, but unfortunately I was not able to build this project from a clean checkout using sbt or IntelliJ, so instead I isolated some tests to an external repository. The last two tests there are failing.

If someone would be willing to help me build jackson-module-scala and/or pair with me on fixing this, jut ping me on twitter @c089.

[timoreimann]

The link you provided to that external repository yields a 404. I suppose you meant to refer to https://github.com/c089/jackson-module-scala-bugreport instead.

[c089]

thanks, fixed

[christophercurrie]

Thanks for the report, I'll take a look. I'm curious, what were your issues building the project?

[c089]

Oh yeah, forgot to add that build log. It's trying to find jackson-core snapshots, but those don't seem to be published so I assume I would have to build that and add it to my local cache?

[warn]  ::::::::::::::::::::::::::::::::::::::::::::::
[warn]  ::          UNRESOLVED DEPENDENCIES         ::
[warn]  ::::::::::::::::::::::::::::::::::::::::::::::
[warn]  :: com.fasterxml.jackson.core#jackson-core;2.5.0-SNAPSHOT: not found
[warn]  :: com.fasterxml.jackson.core#jackson-annotations;2.5.0-SNAPSHOT: not found
[warn]  :: com.fasterxml.jackson.core#jackson-databind;2.5.0-SNAPSHOT: not found
[warn]  ::::::::::::::::::::::::::::::::::::::::::::::
sbt.ResolveException: unresolved dependency: com.fasterxml.jackson.core#jackson-core;2.5.0-SNAPSHOT: not found
unresolved dependency: com.fasterxml.jackson.core#jackson-annotations;2.5.0-SNAPSHOT: not found
unresolved dependency: com.fasterxml.jackson.core#jackson-databind;2.5.0-SNAPSHOT: not found

[christophercurrie]

That's generally not the way I would achieve it. What's probably missing is a reference to the Sonatype OSS repository. I don't like adding that reference to my published build files, because I'll forget to remove it when I do releases. So I keep a sonatype.sbt file in my local build directory with the following contents:

resolvers += "Sonatype OSS Snapshots" at "https://oss.sonatype.org/content/repositories/snapshots"

The published .gitignore file excludes this filename to prevent it from being published. I'll add some build instructions to this effect to the README

[c089]

Ah yes that makes more sense, thanks. Maybe you could add that to README.md to make it a bit easier to get started :)

[christophercurrie]

Ok, so just a heads up, the tests as provided would not work, but that is not the cause of the issue. The issue in the provided tests is the use of classOf:

val result: Option[Int] = mapper.readValue(json, classOf[Option[Int]])

classOf discards any type information that might have been provided, returning the "erased" type, for which Jackson has to deduce the type parameter from the JSON text; no type conversion is done. The correct code for this uses the TypeReference type to retain the type parameter:

val result: Option[Int] = mapper.readValue(json, new TypeReference[Option[Int]]{})

However, this would not fix the underlying issue, which is the same as is reported in #104, and is described in more detail in the FAQ. As describe there, getting the correct behavior involves the use of the @JsonDeserialize annotation. If you have challenges using that annotation, please follow up on the mailing list.

[c089]

oh yes, that makes sense :) Thank for the explanation