EchoController.java

@Path("echo")
public class EchoController {

  private EchoService echoService;

  /**
   * explicit default constructor;
   * required by Jersey
   */
  public EchoController() {
    echoService = new EchoService();
  }

  /**
   * test constructor;
   * required for full control during unit testing
   */
  @TestConstructor
  public EchoController(EchoService echoService) {
    this.echoService = echoService;
  }

  @GET
  @Path("{echo}")
  @Produces(MediaType.TEXT_PLAIN)
  public Echo echo(@PathParam("echo") String echo) {
    return new Echo(echoService.reverse(echo));
  }

}