Apache CXF client to access multiple resourcess

Question

My question might be stupid but I am new in the world of web services and I found a tutorial but I have some doubts about it. It is using Apache CXF. I have the Calculator class which has all the resources, CalculatorStartUp which will startup the server, and the Client class where I have more clients. Bellow is the code:

    import javax.ws.rs.GET;
    import javax.ws.rs.Path;
    import javax.ws.rs.PathParam;
    import javax.ws.rs.Produces;
    import javax.ws.rs.core.MediaType;

    @Path("/calc")
    public class Calculator {

        @GET
        @Path("/add/{a}/{b}")
        @Produces(MediaType.TEXT_PLAIN)
        public String addPlainText(@PathParam("a") double a, @PathParam("b") double b) {
            return (a + b) + "";
        }

        @GET
        @Path("/sub/{a}/{b}")
        @Produces(MediaType.TEXT_PLAIN)
        public String subPlainText(@PathParam("a") double a, @PathParam("b") double b) {
            return (a - b) + "";
        }
    }

Server:

import org.apache.cxf.endpoint.Server;
import org.apache.cxf.jaxrs.JAXRSServerFactoryBean;
import org.apache.cxf.jaxrs.lifecycle.SingletonResourceProvider;

public class CalculatorStartUp {

    public static void main(String[] args) {
         JAXRSServerFactoryBean sf = new JAXRSServerFactoryBean();
            sf.setResourceClasses(Calculator.class);
            sf.setResourceProvider(Calculator.class, 
                new SingletonResourceProvider(new Calculator()));
            sf.setAddress("http://localhost:9999/calcrest/");
            Server server = sf.create();

    }
}

Client:

import org.apache.cxf.jaxrs.client.WebClient;

public class Client {
    final static String REST_URI = "http://localhost:9999/calcrest";
    final static String ADD_PATH = "calc/add";
    final static String SUB_PATH = "calc/sub";
    final static String MUL_PATH = "calc/mul";
    final static String DIV_PATH = "calc/div";

    public static void main(String[] args) {
        int a = 122;
        int b = 34;
        String s = "";

        WebClient plainAddClient = WebClient.create(REST_URI);
        plainAddClient.path(ADD_PATH).path(a + "/" + b).accept("text/plain");
        s = plainAddClient.get(String.class);
        System.out.println(s);

        WebClient plainSubClient = WebClient.create(REST_URI);
        plainSubClient.path(SUB_PATH).path(a + "/" + b).accept("text/plain");
        s = plainSubClient.get(String.class);
        System.out.println(s);
    }

My questions are:

1. why there are two clients? what if I write some resources for the mul and div resources? Do I need to add more resources..why write a client for each resource? there has to be a way to create only one client that can access a certain resource.

2. I saw that when creating a web client you can pass a provider or a list of providers. Can anyone explain what those providers represent?

I would appreciate any help!

Answer 1

For your questions:

1. You can re-use the same WebClient. If you want to re-use it you need to call the WebClient.back(true) or WebClient.replacePath(path) to update the path and can re-use the same baseURI.
2. You can use the WebClient.create(String baseAddress, List<?> providers) where the second argument is to provide JAX-RS provider like JacksonJsonProvider. Providers are used to customize the JAX-RS runtime. WebClient client = WebClient.create(REST_URI, Collections.singletonList(new JacksonJsonProvider()));

More about JAX-RS providers: What does Provider in JAX-RS mean?