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How to Handle Multiple HttpClients in the Same ASP.NET Core Application

It's not impossible that you're accessing several different methods from the same Web Service in your application. If so, and if you're using the HttpClientFactory (and you should be), you have an opportunity to centralize some of your code.

In your Startup class, you should be calling the AddHttpClient method, which, despite its name, actually adds an HttpClientFactory to your application's services collection. As part of that method, you can pass the AddHttpClient method a string and a lambda expression. In the lambda expression you can provide the code to configure the HttpClient objects created by the factory. When it comes time to create an HttpClient object, you can use the string you provided to get the configuration you specified.

This code, for example, passes the AddHttpClient method the name "phvis" and specifies how the BaseAddress on the HttpClient should be set when this factory is used:

services.AddHttpClient("phvis", hc =>
    hc.BaseAddress = new Uri("https://phvis.com/");

Now, when you go to create an HttpClient, you can use "phvis" to get a client that's configured for my site. As an example, this code retrieves an HttpClient configured for phvis.com (see my earlier tip on how to retrieve the factory from the services collection so that you can use it here):

var client = factory.CreateClient("phvis");

Because the client has its BaseAddress property already set, you only have to specify the back part of the service's URL when making a request. This example joins a relative URL passed to the GetAsync method with my earlier BaseAddress to send a request to https://phvis.com/Customer/A123:

var response = await Client.GetAsync("/Customer/A123");

And, if you're accessing multiple Web Services, there's nothing stopping you from setting up multiple named clients, each with their BaseAddress set for the various services you're using.

Posted by Peter Vogel on 09/16/2019 at 11:04 AM

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