groovy-beans-with-jackson

Implementations of the Jackson API to support Groovy Beans, particularly @Immutables

Current Status

[] (https://travis-ci.org/phasebash/groovy-beans-with-jackson)

Use Cases

Groovy Beans are a particularly attractive way of developing Java Beans. Yet when making the most of what Groovy provides, particularly the @Immutable transform, this presents challenges during deserialization as Jackson will not be able to find a default constructor (or any annotations if your classes are fully Groovy).

Consider the following Groovy Bean.

@Immutable
class BeanBag {
    Integer count
    String texture
    Zipper zipper
}

Without modification, this stacktrace might look familiar:

com.fasterxml.jackson.databind.JsonMappingException:
No suitable constructor found for type
[simple type, class BeanBag]:
can not instantiate from JSON object (need to add/enable type information?)

As a first naive step, one could provide a private constructor:

@Immutable
class BeanBag {
    private BeanBag() {}
    Integer count
    String texture
    Zipper zipper
}

And would could expect to receive this message:

Groovyc: Explicit constructors not allowed for @Immutable class: BeanBag

Yet, the @Immutable transform prohibits this, any other constructors are also forbidden.

In Use

In order to deserialize @Immutable GroovyBeans without fuss, simply provide the ObjectMapper with a Jackson Module which provides the necessary ValueInstantiator to allow Jackson to instantiate GroovyBeans by their generated HashMap constructors.

ObjectMapper objectMapper = new ObjectMapper()
objectMapper.registerModule(new GroovyImmutableModule())

// this is now possible.
BeanBag beanBag = objectMapper.readValue('{"count": 100, "texture": "smooth"}', BeanBag)

Coordinates

You may make use of this module with the following coordinates:

Maven

<dependency>
    <groupId>com.phasebash.jackson</groupId>
    <artifactId>groovy-beans-with-jackson-immutables-module</artifactId>
    <version>1.0</version>
</dependency>

Gradle

compile(
    [groupId: 'com.phasebash.jackson', name: 'groovy-beans-with-jackson-immutables-module', version: '1.0']
)

Questions, Feedback?

Feel free to submit an issue ticket through github or contact me directly. I will help you.

License

The groovy-beans-with-jackson has been released under Apache 2.0 as per all it's dependencies.