Jackson is a fast JSON processor for Java that supports three models: streaming, node, and object mapping (akin to the three independent models SAX/[Stax], DOM and JAXB for XML processing).
The object mapping model is a high-level processing model that allows the user to project JSON data onto a domain-specific data model appropriate for their application, without having to deal with the low-level mechanics of JSON parsing. It is the standard object mapping parser implementaton in Jersey, the reference implementation for JSR-311 (Java API for Restful Web Services).
Scala is a functional programming language for the JVM that supports
Java interoperability. Its standard library is quite distinct from Java,
and does not fulfill the expectations of Jacksons default mappings.
Notably, Scala collections do not derive from java.util.Collection or
its subclasses, and Scala properties do not (by default) look like Java Bean properties.
The Scala Module supports serialization and limited deserialization of
Scala Case Classes, Sequences, Maps, Tuples, Options, and Enumerations.
Jackson-module-scala follows the same release strategy of jackson-databind. Master branch is used for Jackson 3 development. The latest releases are v2.12.x.
Scala 2.11, 2. 8DA4 12 and 2.13 are supported. Scala 2.10 support was dropped in v2.12.0. Java 8 is the minimum supported version now.
Scala 3 support will be added in v2.13.0. This support is still deemed to be experimental. Code contributions are welcomed.
- ScalaObjectMapper is not supported for Scala 3 (FasterXML#503)
- v2.13.0-SNAPSHOT is published for Scala 3.0.0
- There are still a number of tests that work with Scala 2 that fail with Scala 3
- It is expected that most use cases should work ok with Scala 3
- Most of the broken tests relate to the use of Jackson annotations - many use cases work but some don't
- There has been no testing of using Scala 3 classes with Scala 2 jackson-module-scala or Scala 2 classes with Scala 3 jackson-module-scala
To use the Scala Module in Jackson, simply register it with the ObjectMapper instance:
// With 2.10 and later
val mapper = JsonMapper.builder()
.addModule(DefaultScalaModule)
.build()
// versions before 2.10 (also support for later 2.x but not 3.0)
val mapper = new ObjectMapper()
mapper.registerModule(DefaultScalaModule)DefaultScalaModule is a Scala object that includes support for all
currently supported Scala data types. If only partial support is desired,
the component traits can be included individually:
val module = new OptionModule with TupleModule {}
val mapper = JsonMapper.builder()
.addModule(module)
.build()You can also mixin ScalaObjectMapper to get rich wrappers that automatically
convert scala manifests directly into TypeReferences for Jackson to use (now depecated because manifests are not supported in Scala 3):
val mapper = new ObjectMapper() with ScalaObjectMapper
mapper.registerModule(DefaultScalaModule)
val myMap = mapper.readValue[Map[String,Tuple2[Int,Int]]](src)This is the equivalent of
val mapper = JsonMapper.builder().addModule(DefaultScalaModule).build()
val myMap = mapper.readValue(src, new TypeReference[Map[String,Tuple2[Int,Int]]]{})Consult the Scaladoc for further details.
The master branch often depends on SNAPSHOT versions of the core Jackson projects,
which are published to the Sonatype OSS Repository. To make these dependencies available,
create a file called sonatype.sbt in the same directory as build.sbt with the following
content. The project .gitignore file intentionally prevents this file from being checked in.
resolvers += "Sonatype OSS Snapshots" at "https://oss.sonatype.org/content/repositories/snapshots"Check out Wiki. API Scaladocs can be found on the project site but they are not really well suited to end users, as most classes are implementation details of the module.
The main mechanisms for contribution are:
- Reporting issues, suggesting improved functionality on Github issue tracker
- Participating in discussions on mailing lists, Gitter (see Jackson portal for details)
- Submitting Pull Requests (PRs) to fix issues, improve functionality.
Currently active core developers (ones who can review, accept and merge Pull Requests) are:
- Morten Kjetland (@mbknor)
- Nate Bauernfeind (@nbauernfeind)
- PJ Fanning (@pjfanning)
If you have questions on issues, implementation strategies, you may refer to core developers (and this is recommended if you are in doubt!), but keep in mind that these are voluntary positions: everyone is doing this because they want to, not because they are paid or contractually obligated to. This also means that time availability changes over time so getting answers may take time.
In addition other Jackson developers with similar access (but less active) include
- Christopher Currie (@christophercurrie) -- original author of Scala module
- Tatu Saloranta (@cowtowncoder) -- main author of core Jackson components
