If you’ve worked with the ASP.NET Core Web API before, chances are you used HttpClient to call them. Although HttpClient directly initializing is a common use, there is a better alternative. Instead of initializing the HttpClient , you use the IHttpClientFactory to get a copy of the HttpClient . Therefore, the resulting HttpClient object can be used to call the Web API. In this article I will discuss 3 ways to get an instance of HttpClient using IHttpClientFactory .

The examples discussed in the article assume you have a Web API as shown below:

ValuesController (a Web API) contains the Get() action, this function returns a string array – Hello World! , Hello Galazy! , and Hello Universe! This Web API is invoked at HomeController . As such, you will need the HttpClient object to complete its task.

See different ways to get an HttpClient instance using the IHttpClientFactory .

The basic technique for obtaining HttpClient

In this technique you use the AddHttpClient() with IServiceCollection inside the ConfigureServices() as shown below:

Next you can inject IHttpClientFactory into HomeController :

Next, you can get the HttpClient instance like this:

Notice how the CreateClient() of the IHttpClientFactory is used to get the HttpClient instance? How to create the instance is the job of CreateClient() . Once you have it, you can configure it according to your needs. For example, here you set the BaseAddress property to create the base address of the Web API. Next you handle to call GetAsync() which is the call to Get() action of Web API.

The JSON data returned from the Get() action is deserialized using the JsonSerializer class of System.Text.Json . Next the data is sent to the Index view on the page.

Obtained from previous configuration and Client name

Sometimes you need instances of HttpClient each have a separate configuration. While calling the AddHttpClient() you can also specify configuration information and names like the following code:

Here, you have created a client named ‘ myclient ‘ that has a certain configuration (in this case, BaseAddress ). Whenever you need this instance you can get it like this:

Notice that the CreateClient() now specifies the name of the client. When ‘ myclient ‘ already has BaseAddress configured in the Startup class, the above code no longer sets the BaseAddress property and handles the GetAsync() method call.

Get a typed client

A typed client is a required configuration packaging, and the Web API calls through a set of methods. The following class implements a typed client:

As you can see, the MyTypedClient class has a public property named Client, which is the type of HttpClient . This property is assigned a value in the constructor through dependency injection. The GetData() does all the configuration of the Web API call and returns the requested data to the client.

Therefore, other parts of the application do not need to know how the API is called or what configuration is needed. Other parts of the system only need to use the MyTypedClient object to get their work done.

When MyTypedClient ready to register in ConfigureServices() as the code below:

To inject the MyTypedClient object in HomeController you would write the following:

Next, you can use the typed client object in the Index() action as shown below:

summary

This article showed 3 ways to create an instance of HttpClient through IHttpClientFactory . HttpClient is popular and easy to use, but it has issues that we need to consider when using. About IHttpClientFactory gives us many more configuration options and features, while making sure to replace what HttpClient can do. You can learn more about their advantages and disadvantages in the article Use HttpClientFactory to implement resilient HTTP requests . Hope to bring you useful things.

The article was translated from source: http://www.binaryintellect.net/articles/1ec182b1-6d47-42da-92b6-c38279b28b20.aspx