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https://github.com/FasterXML/jackson-module-scala

Add-on module for Jackson (https://github.com/FasterXML/jackson) to support Scala-specific datatypes
https://github.com/FasterXML/jackson-module-scala

cbor hacktoberfest jackson json scala serialization smile xml

Last synced: 25 days ago
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Add-on module for Jackson (https://github.com/FasterXML/jackson) to support Scala-specific datatypes

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# Overview



[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, `Sequence`s, `Map`s, `Tuple`s, `Option`s, and Enumerations.



# Version Support



Jackson-module-scala follows the same release strategy of [jackson-databind](https://github.com/FasterXML/jackson-databind).

Master branch is used for Jackson 3 development. The latest releases are v2.12.x.



Scala 2.11, 2.12 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



[Scala 3 support](https://github.com/FasterXML/jackson-module-scala/issues?q=is%3Aissue+is%3Aopen+label%3Ascala3) was added in v2.13.0.

There are a few differences from Scala 2 support.

* ScalaObjectMapper is not supported for Scala 3 but ClassTagExtensions is its replacement. (https://github.com/FasterXML/jackson-module-scala/issues/503)

* 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 https://github.com/FasterXML/jackson-module-scala/labels/scala3

  * 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



# Usage



To use the Scala Module in Jackson, simply register it with the

ObjectMapper instance:



```scala

// 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:



```scala

val module = new OptionModule with TupleModule {}

val mapper = JsonMapper.builder()

  .addModule(module)

  .build()

```



Prior to v2.16.0, `ScalaObjectDeserializerModule` was not part of `DefaultScalaModule`. This module is used to

ensure that deserialization to a Scala object does not create a new instance of the object. Users of older versions can add this

module explicitly.



## DeserializationFeature.FAIL_ON_NULL_CREATOR_PROPERTIES



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 `com.fasterxml.jackson.databind.exc.MismatchedInputException`. By default, the deserialization call will succeed and a `null` value

will be set for the field.



```scala

val mapper = JsonMapper.builder()

  .addModule(DefaultScalaModule)

  .enable(DeserializationFeature.FAIL_ON_NULL_CREATOR_PROPERTIES)

  .build()

```



## ClassTagExtensions

You can also mixin `ClassTagExtensions` to get rich wrappers that automatically

convert scala ClassTags directly into TypeReferences for Jackson to use:

```scala

val mapper = JsonMapper.builder().addModule(DefaultScalaModule).build() :: ClassTagExtensions

// or using old style

//val mapper = new ObjectMapper() with ClassTagExtensions

//mapper.registerModule(DefaultScalaModule)

val myMap = mapper.readValue[Map[String, Tuple2[Int,Int]]](src)

```



ClassTagExtensions is a replacement for `ScalaObjectMapper`, which was recently deprecated because it relies on `Manifest`s and they are not supported in Scala 3.



This is the equivalent of

```scala

val mapper = JsonMapper.builder().addModule(DefaultScalaModule).build()

val myMap = mapper.readValue(src, new TypeReference[Map[String,Tuple2[Int,Int]]]{})

```



Consult the [Scaladoc](https://fasterxml.github.io/jackson-module-scala/latest/api/) for further details.



## Sbt



To import in sbt:

```scala

libraryDependencies += "com.fasterxml.jackson.module" %% "jackson-module-scala" % "2.17.2"

```



## Java/Kotlin users



DefaultScalaModule is a Scala Object and to access it when you are not compiling with Scala compiler, you will need to use `DefaultScalaModule$.MODULE$` instead.



```java

import com.fasterxml.jackson.module.scala.DefaultScalaModule$;



ObjectMapper mapper = JsonMapper.builder().addModule(DefaultScalaModule$.MODULE$).build();

```



# Building



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.



``` scala

resolvers ++= Resolver.sonatypeOssRepos("snapshots")

```



# Download, docs



Check out [Wiki]. API Scaladocs can be found [on the project site][API] but they are not really

well suited to end users, as most classes are implementation details of the module.



# Related Projects

* [jackson-scala-reflect-extensions](https://github.com/pjfanning/jackson-scala-reflect-extensions)

* [jackson-scala3-reflect-extensions](https://github.com/pjfanning/jackson-scala3-reflection-extensions)

* [jackson-module-enumeratum](https://github.com/pjfanning/jackson-module-enumeratum)

* [jackson-module-scala3-enum](https://github.com/pjfanning/jackson-module-scala3-enum) -- since v2.17.0, this is included in jackson-module-scala

* [jackson-caffeine-cache](https://github.com/pjfanning/jackson-caffeine-cache)



# Contributing



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](https://github.com/FasterXML/jackson#participation) for details)

* Submitting Pull Requests (PRs) to fix issues, improve functionality.



## Support



### Community support



Jackson components are supported by the Jackson community through mailing lists, Gitter forum, Github issues. See [Participation, Contributing](../../../jackson#participation-contributing) for full details.



### Enterprise support



Available as part of the Tidelift Subscription.



The maintainers of `jackson-module-scala` and thousands of other packages are working with Tidelift to deliver commercial support and maintenance for the open source dependencies you use to build your applications. Save time, reduce risk, and improve code health, while paying the maintainers of the exact dependencies you use. [Learn more.](https://tidelift.com/subscription/pkg/maven-com.fasterxml.jackson.module.jackson-module-scala.2.13?utm_source=maven-com.fasterxml.jackson.module.jackson-module-scala.2.13&utm_medium=referral&utm_campaign=enterprise&utm_term=repo)



## Core Development Team



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



# Acknowledgements



[![Developed with IntelliJ IDEA](https://www.jetbrains.com/img/logos/logo_intellij_idea.png "Developed with IntelliJ IDEA")](https://www.jetbrains.com/idea/features/scala.html)



[Jackson]: https://github.com/FasterXML/jackson

[SAX]: https://www.saxproject.org/

[DOM]: https://www.w3.org/TR/DOM-Level-3-Core/

[JAXB]: https://jaxb.java.net/

[Jersey]: https://jersey.java.net/

[Java Bean]: https://www.oracle.com/technetwork/java/javase/documentation/spec-136004.html

[Scala]: https://www.scala-lang.org/

[Wiki]: https://github.com/FasterXML/jackson-module-scala/wiki

[API]: https://fasterxml.github.io/jackson-module-scala/latest/api/#com.fasterxml.jackson.module.scala.package