How to catch exception?

Question

I am trying to call api and check its response, but when ever some wrong value is passed it stops the program. I want to add exception during request and response but not sure how to write in function.

This is how i call my REST call

public dynamic APICalls(JObject ljson, string endpoints, string method)
        {
            var httpReq = (HttpWebRequest)HttprequestObject(endpoints, method);
            using (var streamWriter = new StreamWriter(httpReq.GetRequestStream()))
            {
                streamWriter.Write(ljson);
                streamWriter.Flush();
                streamWriter.Close();
            }
            var httpResponse = (HttpWebResponse)httpReq.GetResponse();
            var result = "";
            using (var streamReader = new StreamReader(httpResponse.GetResponseStream()))
            {
                result = streamReader.ReadToEnd();
            }
            return result;
            //return "Success";
            //not sure what to return 
            //here i have to add sql server code to enter into database
        }

THis is code for request

public dynamic HttprequestObject(string endpoints, string method)
        {
            string url = Settings.API_TEST_VALUE + endpoints;
            var httpWebRequest = (HttpWebRequest)WebRequest.Create(url);
            httpWebRequest.ContentType = "application/json";
            httpWebRequest.Method = method;
            return httpWebRequest;
        }

And right before request and right after response i want to catch exception.

At this point i have to catch exception

 var httpResponse = (HttpWebResponse)httpReq.GetResponse();

If some one gives me hint how to catch that before it stops program.

There are 400, 401,402 errors, if something is wrong API sends json

For instance, while creating user :-- Email id already exists

But that points stops json and stops program..

Using try catch it will stop program, I want it to run and want to receive resposne.

Actually, API will send error . For instance, status will be ;---401 UNAUTHORIZED and resposnse will be

{ "reason": "Email already registered.", "success": false }

I am changed my code and

   HttpWebResponse httpResponse; 
            try
            {
               //HttpWebResponse myHttpWebResponse = (HttpWebResponse)httpReq.GetResponse();
               httpResponse = (HttpWebResponse)httpReq.GetResponse();
               //myHttpWebResponse.Close();

               using (var streamReader = new StreamReader(httpResponse.GetResponseStream()))
               {
                   result = streamReader.ReadToEnd();
               }
            }
            catch (WebException e)
            {
                Console.WriteLine("This program is expected to throw WebException on successful run." +
                                    "\n\nException Message :" + e.Message);
                if (e.Status == WebExceptionStatus.ProtocolError)
                {
                    Console.WriteLine("Status Code : {0}", ((HttpWebResponse)e.Response).StatusCode);
                    Console.WriteLine("Status Description : {0}", ((HttpWebResponse)e.Response).StatusDescription);
                }
            }
            catch (Exception e)
            {
                Console.WriteLine(e.Message);
            }

            return result;
            //return "Success";
            //not sure what to return 
            //here i have to add sql server code to enter into database
        }

This is the new code, but I m not getting Json as return value, So i can show specific error. For below Json what should I write?

{ "reason": "Email already registered.", "success": false }

please I m new to c# and if something is not clear please modify or ask question? thank you

There's an entire manual on the C# Programming Language. You should look at it before asking basic questions on the syntax of the language. See C# Programming Guide . For detailed reference, see the C# Reference. — John Saunders
– John Saunders, Commented Jun 5, 2015 at 20:25

Yuval Itzchakov · Accepted Answer · 2015-06-05 20:26:29Z

3

What you're looking for is called a try-catch statement:

try
{
     var httpResponse = (HttpWebResponse)httpReq.GetResponse();
}
catch (WebException e)
{
    // Here is where you handle the exception.
}

Using WebException as the type in the catch statement means only exceptions of that particular type will be caught.

In case an exception occurs, the e variable will contain exception details, such as a message passed from the method which three the exception and any inner exceptions encapsulated inside.

edited Jun 5, 2015 at 20:26

answered Jun 5, 2015 at 20:21

Yuval Itzchakov

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2 Comments

nikunjM Over a year ago

but this will stop my response right ??? Actually, API will send error .For instance, status will be ;---401 UNAUTHORIZED and resposnse will be { "reason": "Email already registered.", "success": false }

Yuval Itzchakov Over a year ago

If GetResponse throws an exception which is caught, the code execution flow will continue normally after the catch block, unless the exception is rethrown.

Yuriy A. · Accepted Answer · 2015-06-05 21:27:27Z

2

You can handle your web exceptions to get HttpStatusCode and Response Message this way:

public void SendAndGetResponseString()
{
    try
    {
        // Here you call your API
    }
    catch (WebException e)
    {
        var result = GetResponceFromWebException(e);
        if (result != null){
            // 
            // Here you could use the HttpStatusCode and HttpResponseMessage
            //
        }                   

        throw;
    }
    catch (Exception e)
    {
        // log exception or do nothing or throw it          
    }
}


private HttpRequestResponce GetResponceFromWebException(WebException e)
{
    HttpRequestResponce result = null;
    if (e.Status == WebExceptionStatus.ProtocolError)
    {
        try
        {
            using (var stream = e.Response.GetResponseStream())
            {
                if (stream != null)
                {
                    using (var reader = new StreamReader(stream))
                    {
                        var responseString = reader.ReadToEnd();
                        var responce = ((HttpWebResponse) e.Response);

                        result = new HttpRequestResponce(responseString, responce.StatusCode);
                    }
                }
            }
        }
        catch (Exception ex)
        {
            // log exception or do nothing or throw it
        }
    }
    return result;
}


public class HttpRequestResponce {
    public HttpStatusCode HttpStatusCode { get;set; }
    public string HttpResponseMessage {get;set;}

    public HttpRequestResponce() { }

    public HttpRequestResponce(string message, HttpStatusCode code)
    {
          HttpStatusCode=code;
          HttpResponseMessage=message;
    }
}

edited Jun 5, 2015 at 21:27

answered Jun 5, 2015 at 20:54

Yuriy A.

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5 Comments

nikunjM Over a year ago

So should i call me response part in catch .. Because its not getting any response if there is error. But I think This will Work..Let me try. Give me 15 mins .. Thank you

Preston Guillot Over a year ago

catch (Exception e) { throw; } does nothing but waste time unwinding the stack needlessly.

nikunjM Over a year ago

@YuriyAkopov I have updated My post, Can you help me with that.. I am not getting response boby... So how to so that can you tell me.. please

Yuriy A. Over a year ago

@user3788832 You added not the full needed code to handle a web exception. Please, look at my example request to facebook api here dl.dropboxusercontent.com/u/46564414/StackOverFlow/… It returns HTTP400 plus error message in json

nikunjM Over a year ago

@YuriyAkopov U can check my ans, In that it is also returning JSon as well as error.. But thanks for your help

Erik Karlstrand · Accepted Answer · 2015-06-05 20:20:29Z

1

You encapsulate whatever method call or code block you want to prevent from throwing unhandled exceptions.

try
{
    // code here
}
catch (Exception)
{
    // here you may do whatever you want to do when an exception is caught
}

answered Jun 5, 2015 at 20:20

Erik Karlstrand

1,5379 silver badges24 bronze badges

6 Comments

Preston Guillot Over a year ago

If you're not going to use the exception object in your handling and you plan on catching any and all exceptions (you shouldn't be planning to do this, normally), declaring the type in the catch expression is unnecessary.

Erik Karlstrand Over a year ago

Sure, it's more of a clarification. To show that you can specify to catch specific exceptions if need be. But yes, it is unnecessary.

nikunjM Over a year ago

@noMad17:-- but this will stop my response right ??? Actually, API will send error .For instance, status will be ;---401 UNAUTHORIZED and resposnse will be { "reason": "Email already registered.", "success": false } –

Erik Karlstrand Over a year ago

If your application throws an exception you will end up inside of the catch-block and from there you can either do nothing at all (wouldn't recommend that since something obviously is wrong) or you can fix the problem with some alternative solution and the code will continue as if nothing happened.

nikunjM Over a year ago

@noMad17 As I mentioned in question, it will return status 401, or 402 or 400.. and it stops.. Let me try try-catch and if I am successfully getting response then i think problem is solved.

|

nikunjM · Accepted Answer · 2015-06-06 04:49:10Z

Ok,Finally I am able to Solve this.. Thanks everyone for you help.

This worked for me. I think I was not reading whole response.. So some how I think I realized and now its working ..

HttpWebResponse httpResponse;
            try
            {
                httpResponse = (HttpWebResponse)httpReq.GetResponse();
                using (var streamReader = new StreamReader(httpResponse.GetResponseStream()))
                {
                    result = streamReader.ReadToEnd();
                }
            }
            catch (WebException e)
            {
                Console.WriteLine("This program is expected to throw WebException on successful run." +
                                    "\n\nException Message :" + e.Message);
                if (e.Status == WebExceptionStatus.ProtocolError)
                {
                    Console.WriteLine("Status Code : {0}", ((HttpWebResponse)e.Response).StatusCode);
                    Console.WriteLine("Status Description : {0}", ((HttpWebResponse)e.Response).StatusDescription);
                    using (Stream data = e.Response.GetResponseStream())
                    using (var reader = new StreamReader(data))
                    {
                        string text = reader.ReadToEnd();
                        Console.WriteLine(text);
                    }
                }
            }
            catch (Exception e)
            {
                Console.WriteLine(e.Message);
            }

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