What is the Java 11 HttpClient and how do you use it for HTTP requests?

The java.net.http.HttpClient (JEP 321, finalised in Java 11) is a modern, non-blocking HTTP client that supports HTTP/1.1 and HTTP/2, WebSockets, synchronous and asynchronous request modes, and streaming. It replaces the antiquated HttpURLConnection.

import java.net.http.*;
import java.net.URI;
import java.time.Duration;

// Build a reusable client (expensive to create — use as singleton)
HttpClient client = HttpClient.newBuilder()
    .version(HttpClient.Version.HTTP_2)
    .connectTimeout(Duration.ofSeconds(10))
    .followRedirects(HttpClient.Redirect.NORMAL)
    .build();

// Synchronous GET
HttpRequest request = HttpRequest.newBuilder()
    .uri(URI.create("https://api.example.com/users/1"))
    .header("Accept", "application/json")
    .timeout(Duration.ofSeconds(30))
    .GET()
    .build();

HttpResponse response =
    client.send(request, HttpResponse.BodyHandlers.ofString());
System.out.println(response.statusCode()); // 200
System.out.println(response.body());       // JSON string

// Asynchronous POST with JSON body
HttpRequest postRequest = HttpRequest.newBuilder()
    .uri(URI.create("https://api.example.com/users"))
    .header("Content-Type", "application/json")
    .POST(HttpRequest.BodyPublishers.ofString("""
        {"name":"Alice","age":30}
        """))
    .build();

client.sendAsync(postRequest, HttpResponse.BodyHandlers.ofString())
    .thenApply(HttpResponse::body)
    .thenAccept(System.out::println)
    .join(); // wait for demo purposes

// With virtual threads (Java 21): use send() (blocking) — no need for sendAsync()
// The virtual thread parks during the network wait — OS thread is free