how to catch exception globally

Question

User-590375999 posted

Hi,

I need to catch the exception globally in web api 2,

how can i throw the exception from the helping classes?

i am using vb.net language, i can't find any guide using vb.net and most of the methods not working in vb.net, showing errors if i convert the c# to vb.net code.

Answer 1

User-369506445 posted

hi

If you want to catch all exception into global method , please follow step by step below

first create a filter class

Imports System.Web.Http.Filters
  
Public Class MyExceptionFilterAttribute 
Inherits ExceptionFilterAttribute

    Public Overrides Sub OnException(actionExecutedContext As HttpActionExecutedContext)
        Dim ex = actionExecutedContext.Exception
         'Here log your exception'
    End Sub
End Class

then add it into WebApiConfig file in App_start folder

  config.Filters.Add(new MyExceptionFilterAttribute())

now create a API action and throw an exception, and put a break point into MyExceptionFilterAttribute  class

you can see after each exception be fire your OnException method in MyExceptionFilterAttribute   class

Answer 2

User-590375999 posted

h,

how to throw the exception to the client with error code and message?

Answer 3

User-369506445 posted

try below code in your API action

  throw new HttpResponseException(Request.CreateErrorResponse(HttpStatusCode.NotFound, 
"this item does not exist"))

Answer 4

User753101303 posted

Hi,

Depends on what happens but usually you don't want to show exceptions that should be solved on your side. For example if the model doesn't validate per your rule you can send back error messages as it should be fixed from the client side but usually you don't want to send exception details if the issue is on your side as for a broken db connection or whatever...

Edit: BTW I would even start at an even higher level such as Application_Error if not AppDomain?UnhandledException (for example if you have code in Application_Start that fails).

Answer 5

User-590375999 posted

Hi,

i can't throw exception from the helper class files.

1. i need to catch the exception at one place and send custom error code and message to the customer

or 

    2. how to throw the exception from the helper class. call from controller methods.

Answer 6

User1120430333 posted

Hi,

i can't throw exception from the helper class files.

1. i need to catch the exception at one place and send custom error code and message to the customer

or 

    2. how to throw the exception from the helper class. call from controller methods.

Granted, the basecontroller is a MVC example, but you also have controllers in the WebAPI. So why can't  you have a basecontroller for WebAPI controllers where all WebAPI controllers are derived from the basecontoller. Any exception thrown in a controller or below the controller is caught by the basecontroller.

https://www.code-sample.com/2014/08/base-controller-in-mvc-5.html

Answer 7

User-369506445 posted

hi sivapooja

did you try my sample ?

as far as i understood your mean , you want catch your error in your helpers class and custom it based on your needs and return to client

if yes please follow below step:

1- create a folder in your root called Filter

2-create a class in Filter folder called MyExceptionFilterAttribute

Imports System.Web.Http.Filters

Public Class MyExceptionFilterAttribute
    Inherits ExceptionFilterAttribute

    Public Overrides Sub OnException(actionExecutedContext As HttpActionExecutedContext)
        Dim ex = actionExecutedContext.Exception

        If (ex.Message.Equals("my Exception")) Then
            Throw New Exception("Generate your custom Exception")
        End If

        'Here log your exception'
    End Sub
End Class

3- in App_start folder in WebApiConfig file put below code :

Imports System
Imports System.Collections.Generic
Imports System.Linq
Imports System.Web.Http

Public Module WebApiConfig
    Public Sub Register(ByVal config As HttpConfiguration)
        ' Web API configuration and services

        ' Web API routes
        config.MapHttpAttributeRoutes()

        config.Routes.MapHttpRoute(
            name:="DefaultApi",
            routeTemplate:="api/{controller}/{id}",
            defaults:=New With {.id = RouteParameter.Optional}
        )


        config.Filters.Add(New MyExceptionFilterAttribute())
    End Sub
End Module

4-create a class called HelperClass

Public Class HelperClass

    Public Function dosomething() As Boolean
        Throw New Exception("my Exception")
    End Function
End Class

5-create a Api Controller called DefaultController

Imports System.Net
Imports System.Web.Http

Namespace Controllers
    Public Class DefaultController
        Inherits ApiController

        ' GET: api/Default
        Public Function GetValues() As IEnumerable(Of String)

            Dim helper As New HelperClass()
            helper.dosomething()

            Return New String() {"value1", "value2"}
        End Function

    End Class
End Namespace

now run your project and fire your API address

http://localhost:50702/api/Default

now you can see your custom exception in browser

Answer 8

User-590375999 posted

Hi Bakkhi,

can throw the exception with status code from outside of controller method  like this?

Throw New HttpResponseException(Request.CreateErrorResponse(HttpStatusCode.InternalServerError, "Internal server error"))

Answer 9

User-369506445 posted

yes you can

for example in your attribute filter put below code :

Imports System.Web.Http
Imports System.Web.Http.Filters

Public Class MyExceptionFilterAttribute
    Inherits ExceptionFilterAttribute

    Public Overrides Sub OnException(actionExecutedContext As HttpActionExecutedContext)
        Dim ex = actionExecutedContext.Exception

        If (ex.Message.Equals("my Exception")) Then

            Throw New HttpResponseException(New Net.Http.HttpResponseMessage(Net.HttpStatusCode.InternalServerError) With
                                    {
                                    .Content = New Net.Http.StringContent("Internal server error")
                                    })
        End If

    End Sub
End Class

Answer 10

User-590375999 posted

Hi bakkhi,

i am getting follow error on OnException method

System.Web.Http.HttpResponseException
  HResult=0x80131500
  Message=Processing of the HTTP request resulted in an exception. Please see the HTTP response returned by the 'Response' property of this exception for details.
  Source=MYAPP
  StackTrace:
   at MYAPP.MYAPPExceptionFilterAttribute.OnException(HttpActionExecutedContext actionExecutedContext) in C:\Users\######\Exception\MYAPPExceptionFilterAttribute.vb:line 7
   at System.Web.Http.Filters.ExceptionFilterAttribute.OnExceptionAsync(HttpActionExecutedContext actionExecutedContext, CancellationToken cancellationToken)

Answer 11

User-369506445 posted

please put your code here

Answer 12

User-590375999 posted

Hi,

Public Class MYAPPExceptionFilterAttribute
    Inherits ExceptionFilterAttribute
    Public Overrides Sub OnException(actionExecutedContext As HttpActionExecutedContext)
     
        Throw New Http.HttpResponseException(New Net.Http.HttpResponseMessage(Net.HttpStatusCode.InternalServerError) With
                                    {
                                    .Content = New Net.Http.StringContent(actionExecutedContext.Exception.Message)
                                    })

    End Sub
End Class

Answer 13

User-369506445 posted

please try <g class="gr_ gr_12 gr-alert gr_spell gr_inline_cards gr_run_anim ContextualSpelling ins-del multiReplace" id="12" data-gr-id="12">belw</g> code 

Public Overrides Sub OnException(actionExecutedContext As HttpActionExecutedContext)
        Dim ex = actionExecutedContext.Exception



        Dim response As New Net.Http.HttpResponseMessage(Net.HttpStatusCode.InternalServerError) With
                                    {
                                    .Content = New Net.Http.StringContent(actionExecutedContext.Exception.Message)
                                    }

        actionExecutedContext.Response = response



    End Sub

Answer 14

User-590375999 posted

Hi,

This will revert the changes? i read if we don't throw error the changes will not be reverted.

Answer 15

User-369506445 posted

if you call your API on a client you can get below message

your status code changed

your message changed

Answer 16

User-590375999 posted

Hi,

This is like send response right? not throwing exception right?

Answer 17

User-590375999 posted

Tested code does not return error message

Answer 18

User-369506445 posted

here are two different ways,

if you want to throw an exception, you have to use first sample code 

if you want change response status code without exception, you have to use last sample code