Triggering asynchronous GET request is a three-step job, as follows:

1. Create a new HttpClient object (java.net.http.HttpClient):

HttpClient client = HttpClient.newHttpClient();

2. Build an HttpRequest object (java.net.http.HttpRequest) and specify the request (by default, this is a GET request):

HttpRequest request = HttpRequest.newBuilder()
  .uri(URI.create("https://reqres.in/api/users/2"))
  .build();

3. Trigger the request and wait for the response (java.net.http.HttpResponse). Being a synchronous request, the application will block until the response is available:

HttpResponse<String> response 
  = client.send(request, BodyHandlers.ofString());

If we group these three steps and add the lines for displaying the response code and body at the console, then we obtain the following code:

HttpClient client = HttpClient.newHttpClient();

HttpRequest request = HttpRequest.newBuilder()
  .uri(URI.create("https://reqres.in/api/users/2"))
  .build();

HttpResponse<String> response 
  = client.send(request, BodyHandlers.ofString());

System.out.println("Status code: " + response.statusCode());
System.out.println("
 Body: " + response.body());

One possible output for the preceding code is as follows:

Status code: 200
Body:
{
  "data": {
    "id": 2,
    "email": "[email protected]",
    "first_name": "Janet",
    "last_name": "Weaver",
    "avatar": "https://s3.amazonaws.com/..."
 }
}

By default, this request takes place using HTTP/2. However, we can explicitly set the version via HttpRequest.Builder.version() as well. This method gets an argument of the HttpClient.Version type, which is an enum data type that exposes two constants: HTTP_2 and HTTP_1_1. The following is an example of explicitly downgrading to HTTP/1.1:

HttpRequest request = HttpRequest.newBuilder()
  .version(HttpClient.Version.HTTP_1_1)
  .uri(URI.create("https://reqres.in/api/users/2"))
  .build();

The default settings for HttpClient are as follows:

• HTTP/2
• No authenticator
• No connection timeout
• No cookie handler
• Default thread pool executor
• Redirection policy of NEVER
• Default proxy selector
• Default SSL context

We'll take a look at the query parameter builder in the next section.