Adding jar to classpath for runtime requirement

Question

I am getting this error java.lang.NoCLassDefFoundError: org/apache/http/HttpEntity when I run my application. It compiles and builds fine. But then I try to use an EJB that imports a HttpClient, I get this error.

As I have read, that I have to import the jars (httpclient-4.5 and httpcore-4.4.5) at runtime. How do I do that?

I have these jars in my gradle script. I would think that the compile would take care of pulling in all of the classes it needs to build and be good to run.

I have a implication of the HttpClient in a class. Below is a slimmed down version of the implementation:

import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;

public class httpClientImpl implements httpClient {

    public CloseTrailerResponse closeActionFromAdapter(requestObject request) throws IOException {

        CloseableHttpClient client = HttpClients.createDefault();
        HttpPost httpPost = new HttpPost(trailerCloseAdapterURL);

        try {
            ..setting stuff     
            CloseableHttpResponse response = client.execute(httpPost);      
            }       
        }
        catch(Exception ex) {
            //exceptions logged
        }
       finally {
        client.close();
       }
        return response;
    }
}

This client is instantiated and called in the EJB.

import com.client.httpClientImpl;

private HttpClientImpl httpClientInstance = new HttpClientImpl();
private Request request;
private Response response;

//In a method the http client is called...
response = httpClientInstance.closeActionFromAdapter(request); 

When I access this class at runtime, I get the class def not found.

Is the error that it needs the class at runtime or is it something else? If it needs the class at runtime, how do I add it to the classpath?

Thanks.