JAX-RS/RestEasy Client and JSON-P - jax-rs

Question

In a REST client written using JAX-RS and RestEasy as implementation I'm trying the send a JsonObject via POST to a WebService. The project uses the reference implementation of JSON-P, org.glassfish.javax.json.
When I'm trying the send the request I get the following exception:
javax.ws.rs.ProcessingException: RESTEASY003215: could not find writer for content-type application/json type: org.glassfish.json.JsonObjectBuilderImpl$JsonObjectImpl
The following artifacts are present in the pom.xml:
<dependency>
<groupId>javax.json</groupId>
<artifactId>javax.json-api</artifactId>
<version>1.1.4</version>
</dependency>
<dependency>
<groupId>org.glassfish</groupId>
<artifactId>javax.json</artifactId>
<version>1.1.4</version>
</dependency>
<dependency>
<groupId>org.jboss.resteasy</groupId>
<artifactId>resteasy-jaxrs</artifactId>
<version>3.6.3.SP1</version>
</dependency>
<dependency>
<groupId>org.jboss.resteasy</groupId>
<artifactId>resteasy-client</artifactId>
<version>3.6.3.SP1</version>
</dependency>
<dependency>
<groupId>org.jboss.resteasy</groupId>
<artifactId>resteasy-json-p-provider</artifactId>
<version>3.6.3.SP1</version>
</dependency>
From what I've read in the documentation that should be all necessary.
The request in invoked as follows:
final JsonObjectBuilder credentialsBuilder = Json.createObjectBuilder();
credentialsBuilder.add("username", configuration.getServiceUser());
credentialsBuilder.add("password", configuration.getServicePassword());
final Entity<JsonObject> credentials = Entity
.json(credentialsBuilder.build());
final Response response = ClientBuilder
.newClient()
.target("http://www.example.org/some/url")
.request(MediaType.APPLICATION_JSON)
.post(credentials);
What I'm missing?

Answer 1

It seems like your provider is not being registered; depending on how/where you're using Resteasy, you might need to do additional configuration to make sure it picks up that kind of stuff for you (http://docs.jboss.org/resteasy/docs/3.6.3.Final/userguide/html_single).
For example, if you're using servlet configuration, you might need to use resteasy-servlet-initializer, or add in a spring helper, etc.
Note that you can most likely explicitly register the JSON-P provider to the Client, Target, or Request itself when you're building it out if you wanted to (or are just testing)

Answer 2

Thanks for the hint. That was indeed the solution. The application is a command line client (Java SE). The solution was - in addition to add the dependencies - to do register the providers when creating the client instance:
ClientBuilder
.newClient()
.register(JsonArrayProvider.class)
.register(JsonObjectProvider.class)
.register(JsonStructureProvider.class)
.register(JsonValueProvider.class)
... // create request