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. 3.x branch is used for Jackson 3 development.
Scala 2.12, 2.13, 3.3+ are supported. Scala 2.11 support was dropped in v3.0.0. Java 17 is the minimum supported version now (Jackson 3 generally has a minimum requirement of Java 17).
There are a few differences from Scala 2 support.
- There are still a few tests that work with Scala 2 that fail with Scala 3
- It is expected that most use cases should work ok with Scala 3
- Known issues with using jackson-module-scala with Scala 3 are tracked at scala3
- There has been limited 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:
val mapper = JsonMapper.builder()
.addModule(DefaultScalaModule)
.build()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 (approach differs from Jackson 2):
val scalaModule = ScalaModule.builder()
.addModule(OptionModule)
.addModule(TupleModule)
.build()
val mapper = JsonMapper.builder()
.addModule(scalaModule)
.build()If you want to configure the behavior of the ScalaModule but have all the underlying Scala modules, you can do this :
val scalaModule = ScalaModule.builder()
.addAllBuiltinModules()
.addModule(TupleModule)
.build()
val mapper = JsonMapper.builder()
.addModule(scalaModule)
.applyDefaultValuesWhenDeserializing(false) //default of true
.supportScala3Classes(false) //default of true
.build()It is recommended that Scala users enable DeserializationFeature.FAIL_ON_NULL_CREATOR_PROPERTIES. This feature means that when you
deserialize JSON and bind to a Scala/Java class and a required field is missing (or null), then the deserialization call will fail
with a tools.jackson.databind.exc.MismatchedInputException. By default, the deserialization call will succeed and a null value
will be set for the field.
val mapper = JsonMapper.builder()
.addModule(DefaultScalaModule)
.enable(DeserializationFeature.FAIL_ON_NULL_CREATOR_PROPERTIES)
.build()You can also mixin ClassTagExtensions to get rich wrappers that automatically
convert scala ClassTags directly into TypeReferences for Jackson to use:
val mapper = JsonMapper.builder().addModule(DefaultScalaModule).build() :: ClassTagExtensions
val myMap = mapper.readValue[Map[String, Tuple2[Int,Int]]](src)ClassTagExtensions is a replacement for ScalaObjectMapper, which was recently deprecated because it relies on Manifests and they are not supported in Scala 3.
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.
To import in sbt:
libraryDependencies += "tools.jackson.module" %% "jackson-module-scala" % "3.0.0-rc1-SNAPSHOT"DefaultScalaModule is a Scala Object and to access it when you are not compiling with Scala compiler, you will need to use tools.jackson.module.scala.javadsl.DefaultScalaModule.getInstance() instead. You can access the Scala object using tools.jackson.module.scala.DefaultScalaModule$.MODULE$.
import tools.jackson.module.scala.javadsl.*;
ObjectMapper mapper = JsonMapper.builder().addModule(DefaultScalaModule.getInstance()).build();
// or ScalaModule.builder().addAllBuiltinModules().build() instead of DefaultScalaModule.getInstance()The branches 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 ++= Resolver.sonatypeOssRepos("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.
- jackson-scala-reflect-extensions
- jackson-scala3-reflect-extensions
- jackson-module-enumeratum
- jackson-caffeine-cache
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.
Jackson components are supported by the Jackson community through mailing lists, Gitter forum, Github issues. See Participation, Contributing for full details.
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Currently active core developers (ones who can review, accept and merge Pull Requests) are:
- 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
- Morten Kjetland (@mbknor)
- Nate Bauernfeind (@nbauernfeind)
- Tatu Saloranta (@cowtowncoder) -- main author of core Jackson components
