Extension types

At the moment you can find two kind of extensions in Genson,

  • Integrations of Genson in common frameworks to handle the JSON ser/deser.
  • Integration in Genson of types defined in widely used libraries, ie. support JSR 353 JsonObject, JsonArray, etc types. This is done through the GensonBundle system.


A GensonBundle is a way to group a set of features in a single registrable component. Bundles by default, are not registered, you must do it explicitly. This is used internally to support types and annotations defined in other libraries and is intended to allow users to group their customizations behind a logical abstraction - the bundle.

User config takes precedence over bundle config. This means that you can override the configuration that a bundle defined, but at your own risk. Maybe the bundle did need this specific configuration in order to work properly.

Bundles must be registered first, before any other configuration.

For example you can implement a Bundle providing some common features for your company.

public class MyBundle extends GensonBundle {
  public void configure(GensonBuilder builder) {
    // use the builder to configure & register your components

// then register your bundle
Genson genson = new GensonBuilder().withBundle(new MyBundle()).create();

JAX-RS: Jersey & cie

To enable json support in JAX-RS implementations with Genson, just drop the jar into your classpath. The implementation will detect it and use Genson for json conversions.

Actually it has been tested with Jersey and Resteasy. It works out of the box.


  • By default Genson JAX-RS integration enables JAXB annotations and constructors without arguments support.

Manual registration

The examples above are for Jersey, but ResourceConfig is just an implementation of Application interface. So you can achieve the same result without using Jersey but any other implementation of Jax-RS spec. You basically only have to implement getSingletons to return a Set containing your GensonJaxRSFeature instance or GensonJsonConverter.

To manually register Genson in Jersey, on the server side:

// You can also provide an instance of GensonJsonConverter.
final ResourceConfig config = new ResourceConfig().register(GensonJsonConverter.class);

On the client side:

final ClientConfig clientConfig = new ClientConfig().register(GensonJsonConverter.class);

Adding a customized Genson instance can be achieved through the same registration mechanism.


In many cases you might want to customize the Genson instance being used. To do so, you only have to create your custom instance with GensonBuilder and then register a GensonJaxRSFeature configured with this Genson instance.

new ResourceConfig().register(new GensonJaxRSFeature().use(myCustomGenson).disableSerializationFor(String.class));

GensonJaxRSFeature is supposed to be the centralized place containing the config related to Genson and Jax-RS.

Disabling Genson in JAX-RS

Disabling Genson is achieved via GensonJaxRSFeature mechanism we have seen above.

// client
ClientBuilder.newClient(new ClientConfig().register(new GensonJaxRSFeature().disable()));
// server
new ResourceConfig().register(new GensonJaxRSFeature().disable());

Filtering properties from ser/de at runtime

The Jax-Rs extension comes with a feature called UrlQueryParamFilter which implements Gensons RuntimePropertyFilter. Let’s say we have a class containing some properties age, name, gender and we want to be able to include only some of those at runtime in the response based on the params of the query string. For example having this url http://localhost/foo/bar?filter=age&filter=name would include only age and name in the response.

To enable this feature you must register it with Genson and with Jax-Rs:

UrlQueryParamFilter filter = new UrlQueryParamFilter();
Genson genson = new GensonBuilder().useRuntimePropertyFilter(filter).create();
new ResourceConfig()
  .register(new GensonJaxRSFeature().use(genson))

Have a look at the methods from UrlQueryParamFilter to see how its behaviour can be customized to fit your needs.

JSR 353 - Java API for Json Processing

Genson provides two kind of integrations with the JSR. You can use it as the JSR implementation or to work with the DOM structures defined in the JSR.

If the JSR API is not included in your Java version, you can still get it with Maven.


Using Genson as JSR 353 implementation

Since version 0.99 Genson provides a complete implementation of JSR 353. To use Genson implementation, you only need it on your classpath.

Using JSR 353 types with Genson

Starting with release 0.98 Genson provides a bundle JSR353Bundle that enables support of JSR 353 types in Genson. This means that you can ser/deser using those types but also mix them with the databinding mechanism.

Genson genson = new GensonBuilder().withBunle(new JSR353Bundle()).create();
JsonObject object = genson.deserialize(json, JsonObject.class);

You can also mix with standard Pojos.

class Pojo {
  public String aString;
  public JsonArray someArray;

Pojo pojo = genson.deserialize(json, Pojo.class);

JAXB Annotations

Since version 0.95 Genson provides support for JAXB annotations. All annotations are not supported as some do not make sense in the JSON world. Genson annotations take precedence over JAXB ones, so they can be used to override JAXB annotations.

In Jersey JAXB bundle is enabled by default. If you are using Genson outside Jersey you have to register JAXB bundle:

Genson genson = new GensonBuilder().withBundle(new JAXBBundle()).create();

Supported annotations

  • XmlAttribute can be used to include a property in serialization/deserialization (can be used on fields, getter and setter). If a name is defined it will be used instead of the one derived from the method/field.

  • XmlElement works as XmlAttribute, if type is defined it will be used instead of the actual one.

  • XmlJavaTypeAdapter can be used to define a custom XmlAdapter. This adapter must have a no arg constructor.

  • XmlEnumValue can be used on enum values to map them to different values (it can be mixed with default behaviour: you can use this annotation on some enum values and let the others be ser/deser using the default strategy).

  • XmlAccessorType can be used to define how to detect properties (fields, methods, public only etc).

  • XmlTransient to exclude a field or get/set from ser/deser process.

  • XmlRootElement by default has no effect, but when used with new JAXBBundle().wrapRootValues(true) allows to wrap/unwrap the root classes annotated with @XmlRootElement in another object. By default the key used is the class name with first letter to lower case.

Supported types

Actual implementation has default converters for Duration and XMLGregorianCalendar.

What might come next

Support for cyclic references using XmlId and XmlIdRef, XmlType.

If there are other jaxb features you would like to be supported just open an issue or drop an email on the google group.


Genson provides JodaTimeBundle enabling joda-time types support.

Genson genson = new GensonBuilder().withBundle(new JodaTimeBundle()).create();

By default subclasses of ReadableInstant are being ser/de using


formatter. You can change it and use another formatter. However take care, that this formatter will be used for serialization and deserialization, thus it must support the methods print and parse.

DateTimeFormatter formatter = DateTimeFormat.forPattern("yyyy/MM/dd");
Genson genson = new GensonBuilder()
  .withBundle(new JodaTimeBundle().useDateTimeFormatter(formatter))

LocalDate/DateTime/Time are serialized using their ISODateTimeFormat.date/dateTime/time formats with default DateTimeZone. However LocalDateTime and LocalTime are being deserialized using localDateOptionalTimeParser and localTimeParser. In most cases you won’t need to configure the deserialization format for these types.

JsonDateFormat annotation can also be used with DateTime, MutableDateTime, LocalDate, LocalDateTime and LocalTime classes.

Supported types

Main Joda Time types are supported at the moment, if some are missing feel free to open an issue or even better, make a pull request :)

  • Implementations of ReadableInstant such as DateTime, Instant and MutableDateTime.
  • LocalDate, LocalDateTime and LocalTime
  • Interval as an object containing two keys start and end, using the configured DateTimeFormatter or timestamps.
  • Period is ser/de using


  • Duration is ser/de as a long representing the duration in milliseconds.


At the moment the Guava bundle is still under development, it only supports the Optional type. Absent will be serialized as null and null will be deserialized back to Absent.

Genson genson = new GensonBuilder().withBundle(new GuavaBundle()).create();

Spring MVC

To enable json support in Spring MVC with Genson, you need to register Gensons MessageConverter implementation.

    <bean class="com.owlike.genson.ext.spring.GensonMessageConverter"/>