This project is no longer maintained!

gson library heavily depends on reflection and so it's hard to keep the support for Scala. Use json4s or circe library instead.

gson-scala

Allows to use Scala and Java 8 types with gson library.

Supported types:

• java.time.Instant
• java.time.Duration
• scala.concurrent.duration.Duration
• java.util.Optional
• scala.Option
• scala.Seq

How to use

<dependency>
    <groupId>cz.augi.gsonscala</groupId>
    <artifactId>gson-scala_2.12</artifactId>
    <version>$latestVersion</version>
</dependency>

compile "cz.augi.gsonscala:gson-scala_2.12:$latestVersion"

import cz.augi.gsonscala._
val gson = new GsonBuilder()
                .registerMillisDurationConverters() // registers for Duration classes expecting millis in integer values
                .registerUnixMillisInstantConverter() // registers for Instant expecting Unix millis in integer values
                .registerBasicConverters() // registers for Optional, Option and Seq
                .create()

The registerBasicConverters``must be called as the last method before the create` method.

Alternatively, these methods can be used for registrations:

• registerSecondsDurationConverters - expects durations in seconds
• registerStringDurationConverters
• registerUnixSecondsInstantConverter - expects time in Unix timestamp (seconds)
• registerStringInstantConverter - expects time in ISO format

You can also cherry-pick some of converters as shown here.

Please note that registerBasicConverters also registers NonNullTypeAdapterFactory - it's required because the default object deserializer doesn't call deserializer of a field if the value is not even present in the json.

Why to use this library?

As gson library targets Java 6, it doesn't support Java 8 type out of the box. There are several libraries that add support for Optional type but most of them is not able to handle missing value correctly.

For example gson-java8-datatype looked promising but it has too simple tests. E.g. if you have a class with Optional field then the deserialized object contains null instead of Optional.empty().

The problem is that gson by default doesn't write null values. So the read method of TypeAdapter is not even called for missing value and the field of deserialized object has null value. Tests of gson-java8-datatype are passing because null value is written if it's top-level object.