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You're Using HttpClient Wrong

There's a very good chance that, every time you need to access a Web Service, you've been creating an HttpClient object and then throwing it away. Unfortunately, that's bad for your application because you can run out of WebSockets (yes, even if you call the object's Dispose method before discarding it). Though, I have to admit, you'll only have this problem if you use the HttpClient a lot. Still, it's a bad idea to keep creating and destroying it.

In the .NET Framework, the intent was for you to create the HttpClient once in your application and use it over and over. To do that you'll have to declare your HttpClient object as a global or static variable. That creates its own problems, of course.

In ASP.NET Core, however, you have a better option: the HttpClientFactory. The HttpClientFactory provides you with HttpClient objects but takes responsibility for managing the resources that the clients can use up. Think of it as "connection pooling for Web Services."

The first step in implementing this tactic is to create an HttpClientFactory object in your project's Startup class in the ConfigureServices method and add it to your application's services collection. All you need is this code (and, yes, I realize that the method's name doesn't do a good job of reflecting what it does):

services.AddHttpClient();

Then, in the constructor for any controller that needs an HttpClient, you can ask for the factory by its interface (IHttpClientFactory). This following example grabs the HttpClientFactory out of the services collection and stuffs it into a field to be used by the methods in the controller:

public class TodoListController: Controller
{
  public TodoListController(IHttpClientFactory factory, ... )
 {
  this.factory = factory;

Now, whenever you need an HttpClient object, you just get it from the factory's Create method, like this:

HttpClient hc = factory.CreateClient();

Posted by Peter Vogel on 09/12/2019 at 12:27 PM


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