Using ASP.NET Web API to call Java Web Service

Question

I have an ASP.NET Web API which is supposed to call a java addition web service. When i run the java web service and type url http://localhost:8080/addition/9/6 i get {"firstNumber":9,"secondNumber":6,"sum":15}as the output data. Right now, i want to use the ASP.NET Web API to call and display that data when i run the ASP.NET Web API application. How do i go about doing that?

Here are my codes:

ASP.NET Web API Codes

RestfulClient.cs

public class RestfulClient     
{
    private string BASE_URL = "http://localhost:8080/addition/";
    public Task<string> addition()
    {
        {
            try
            {
                var client = new HttpClient();
                client.BaseAddress = new Uri(BASE_URL);
                client.DefaultRequestHeaders.Accept.Add(
                    new MediaTypeWithQualityHeaderValue("application/json"));
                HttpResponseMessage response = client.GetAsync("addition").Result;
                return response.Content.ReadAsStringAsync();                 
            }
            catch (Exception e)
            {
                HttpContext.Current.Server.Transfer("ErrorPage.html");
            }
            return null;
        }
    }
}

ApiController.cs

private RestfulClient restfulClient = new RestfulClient();

    public ActionResult Index()
    {

        var Result1 = restfulClient.addition().Result;
        return Content(Result1);
    }

Java Web Service Codes

AdditionController.java

@RestController
public class AdditionController {

private static final String template = " %s";
private static int getSum;

@RequestMapping("/addition/{param1}/{param2}")
@ResponseBody 

public Addition getSum 
            (@PathVariable("param1") int firstNumber,@PathVariable("param2") int secondNumber) {
return new Addition(
        (String.format(template, firstNumber)), String.format(template, secondNumber));
  }
}

Someone please help me. Thank you so much in advance.

Not related to your issue, but please make your HttpClient a static instance through your application (see MSDN and this blog post). — ProgrammingLlama
– ProgrammingLlama, Commented Oct 27, 2017 at 1:56
By the way, you have to await async methods, otherwise you don't get their results. See here. — ProgrammingLlama
– ProgrammingLlama, Commented Oct 27, 2017 at 1:58
At first, when my java web service did not take in any parameters, this restfulClient.cs class worked. However when i added parameters to my java web service, this class does not work. I am not sure on how i should edit it. Could you please guide me through? — Susmitha Naidu
– Susmitha Naidu, Commented Oct 27, 2017 at 3:50

Susmitha Naidu · Accepted Answer · 2017-10-27 09:00:08Z

According to the Java service, the URL you are calling from the client is not formatted correctly based on your base URL and the one used in the GetAsync.

public class RestfulClient {
    private static HttpClient client;
    private static string BASE_URL = "http://localhost:8080/";

    static RestfulClient() {
        client = new HttpClient();
        client.BaseAddress = new Uri(BASE_URL);
        client.DefaultRequestHeaders.Accept.Add(
            new MediaTypeWithQualityHeaderValue("application/json"));
    }

    public async Task<string> addition(int a, int b) {
        try {
            var endpoint = string.Format("addition/{0}/{1}", a, b);
            var response = await client.GetAsync(endpoint);
            return await response.Content.ReadAsStringAsync();                 
        } catch (Exception e) {
            HttpContext.Current.Server.Transfer("ErrorPage.html");
        }
        return null;
    }
}

The controller would also need to be updated.

public async Task<ActionResult> Index() {
    int a = 9;
    int b = 6;
    var result = await restfulClient.addition(a, b);
    return Content(result);
}

Note the proper use of the HttpClient as suggested in the comments and as well as the use of async/await.

I get the error An object reference is required for the non-static field, method, or property 'RestfulClient.BASE_URL'

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