NoClassDefFoundError when calling function from RESTful web service - rest

Question

I'm trying to create a RESTful web service in java that will allow authentication with a Yubikey.
I'm modifying an existing tutorial that I completed while trying to learn about REST.
I'm trying to call the validation function from within the javax.ws.rs.core.Response function but keep getting an error with a package from the imported yubikey jars.
I imported these jars from build path -> libraries --> Add external Jars
Error as follows when I post my form to the RESTful url:
java.lang.NoClassDefFoundError: com/yubico/client/v2/exceptions/YubicoValidationException
package de.vogella.jersey.todo.resources;
import javax.ws.rs.FormParam;
import javax.ws.rs.POST;
import javax.ws.rs.Path;
import javax.ws.rs.core.Response;
import com.yubico.client.v2.exceptions.YubicoValidationException;
import com.yubico.client.v2.exceptions.YubicoValidationFailure;
import de.vogella.jersey.todo.resources.Validate;
#Path("/test")
public class Test {
#POST
public Response testCred(#FormParam("username") String username,
#FormParam("password") String password,
#FormParam("otp") String otp) throws YubicoValidationException, YubicoValidationFailure {
int client_id = 11095;
boolean status;
status = Validate.validate(otp, client_id);
return Response.status(200)
.entity("validation status: : " + status + ", for client " + otp)
.build();
}
}
the validate class is as follows:
package de.vogella.jersey.todo.resources;
import com.yubico.client.v2.YubicoClient;
import com.yubico.client.v2.YubicoResponse;
import com.yubico.client.v2.YubicoResponseStatus;
import com.yubico.client.v2.exceptions.YubicoValidationException;
import com.yubico.client.v2.exceptions.YubicoValidationFailure;
public class Validate {
public static boolean validate(String otp, int client_id) throws YubicoValidationException, YubicoValidationFailure {
YubicoClient client = YubicoClient.getClient(client_id);
YubicoResponse response = client.verify(otp);
if(response != null && response.getStatus() == YubicoResponseStatus.OK) {
return true;
}
return false;
}
}