How to solve could not find writer for content-type application/json type

In this short tutorial we will learn how to fix a common error that you can hit when deploying REST Web service that produce or consume JSON content type.

Error description:

RESTEASY004655: Unable to invoke request: jakarta.ws.rs.ProcessingException: RESTEASY003215: could not find writer for content-type application/json type: 

A common cause of this issue is that you are either:

• Missing a JSON Provider such as Jackson2. Jackson is is a multi-purpose Java library for processing JSON data format.
• An incorrect version of Resteasy Client

Example of the correct dependencies for a RESTeasy Endpoint that produces/consumes JSON Media type:

<dependency>
    <groupId>org.jboss.resteasy</groupId>
    <artifactId>resteasy-client</artifactId>
    <version>6.2.0.Final</version>
</dependency>

<dependency>
    <groupId>org.jboss.logging</groupId>
    <artifactId>commons-logging-jboss-logging</artifactId>
    <version>1.0.0.Final</version>
</dependency>

<dependency>
  <groupId>org.jboss.resteasy</groupId>
  <artifactId>resteasy-jackson2-provider</artifactId>
  <version>6.2.0.Final</version>
</dependency>

Sample JAX-RS Application that consumes/produces JSON media type

Here is a minimal REST Endpoint you can use as an example:

@Path("/service")
@Produces(MediaType.APPLICATION_JSON)
@Consumes(MediaType.APPLICATION_JSON)
public class ParamRESTService {

	@Inject DataList ejb;

	@GET
	@Path("/{id}")
	public SimpleProperty getPropertyById(@PathParam("id")int id)
	{
		return ejb.getList().get(id);
	}

	@GET
	public List<SimpleProperty> getProperty()
	{
		return ejb.getList();
	}

	@POST
	public Response createProperty(  SimpleProperty p) {
		int n = ejb.addToList(p);
		return Response.status(Response.Status.OK).build();
	}
}

The DataList is an EJB that stores an ArrayList of a Java POJO in memory:

@ApplicationScoped
@Named
public class DataList implements Serializable {
	private List<SimpleProperty> list;

	@PostConstruct
	public void init() {
		list = new ArrayList<SimpleProperty>();

	}
	public List<SimpleProperty> getList() {
		return list;
	}

	public void setList(List list) {
		this.list = list;
	}
	public int addToList(String key, String value) {

		list.add(new SimpleProperty(key,value));
		return list.size();
	}
	public int addToList(SimpleProperty p) {
		list.add(p);
		return list.size();
	}

}

Testing the REST Service

In order to Test the REST Service you can use the following JUnit Test Class:

public class TestClient {
String BASE_URL ="http://localhost:8080/ee-rest-client/rest";

	@Test
	public void testParam() {
		Client client = ClientBuilder.newClient();
		SimpleProperty p1 = new SimpleProperty("mykey","value");

		WebTarget myResource = client.target(BASE_URL).path("/service");
		Response rs = myResource.request(MediaType.APPLICATION_JSON)
						.post(Entity.json(p1), Response.class);

		assertEquals(rs.getStatus(),200);

		SimpleProperty property =
				client.target(BASE_URL).path("/service/{key}")
				        .resolveTemplate("key", "0")
						.request(MediaType.APPLICATION_JSON)
						.get(SimpleProperty.class);
		assertNotNull(property);

        List<SimpleProperty> result = client.target(BASE_URL).path("/service")
            .request(MediaType.APPLICATION_JSON).get(new GenericType<List<SimpleProperty>>() {
            });

		assertEquals("mykey",result.get(0).getKey());
		assertEquals("value",result.get(0).getValue());

	}

}

Conclusion

This article was a quick howto to help you with the error “RESTEASY003215: could not find writer for content-type application/json type:”.