Java HttpClient (Java 11+): GET, POST, Headers, Async Requests and Sockets

Since Java 11, the JDK includes a modern HttpClient (java.net.http) for HTTP/1.1 and HTTP/2 calls with no extra library. Testers use it for small utilities: checking links, seeding test data, calling a health endpoint before a suite. For full API test suites, REST Assured is usually more convenient.

// ── HTTP CLIENT (Java 11+) ──
import java.net.http.*;
import java.net.URI;

HttpClient client = HttpClient.newBuilder()
    .version(HttpClient.Version.HTTP_2)
    .connectTimeout(Duration.ofSeconds(10))
    .build();

// GET request
HttpRequest getReq = HttpRequest.newBuilder()
    .uri(URI.create("https://api.example.com/users"))
    .header("Accept", "application/json")
    .header("Authorization", "Bearer " + token)
    .GET()
    .build();

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

// POST request
String json = "{\"name\":\"Alice\",\"email\":\"alice@test.com\"}";
HttpRequest postReq = HttpRequest.newBuilder()
    .uri(URI.create("https://api.example.com/users"))
    .header("Content-Type", "application/json")
    .POST(HttpRequest.BodyPublishers.ofString(json))
    .build();

// Async request
client.sendAsync(getReq, HttpResponse.BodyHandlers.ofString())
    .thenApply(HttpResponse::body)
    .thenAccept(System.out::println)
    .join();

// ── SOCKETS (low-level) ──
// Server
ServerSocket server = new ServerSocket(8080);
Socket client = server.accept();  // blocks waiting for connection
BufferedReader in = new BufferedReader(new InputStreamReader(client.getInputStream()));
PrintWriter out = new PrintWriter(client.getOutputStream(), true);
String message = in.readLine();
out.println("Echo: " + message);
client.close();

// Client
Socket socket = new Socket("localhost", 8080);
PrintWriter out2 = new PrintWriter(socket.getOutputStream(), true);
BufferedReader in2 = new BufferedReader(new InputStreamReader(socket.getInputStream()));
out2.println("Hello Server!");
System.out.println(in2.readLine());  // Echo: Hello Server!
socket.close();

Reading JSON Responses

record User(int id, String name, String email) { }

HttpResponse<String> res = client.send(getReq, HttpResponse.BodyHandlers.ofString());
if (res.statusCode() != 200) {
    throw new IllegalStateException("GET /users/7 returned " + res.statusCode() + ": " + res.body());
}
ObjectMapper mapper = new ObjectMapper();                    // Jackson
User user = mapper.readValue(res.body(), User.class);

Timeouts and Retries

HttpRequest req = HttpRequest.newBuilder(URI.create(baseUrl + "/health"))
        .timeout(Duration.ofSeconds(5))                    // per-request timeout
        .GET().build();

for (int attempt = 1; attempt <= 3; attempt++) {           // wait for the environment before the suite
    try {
        if (client.send(req, HttpResponse.BodyHandlers.discarding()).statusCode() == 200) break;
    } catch (HttpTimeoutException e) { /* retry */ }
    Thread.sleep(2000);
}

Set a connect timeout on the client and a request timeout on each call; without them a hung server can block a test run indefinitely.

HttpClient vs REST Assured

FAQs

Which Java version introduced HttpClient?

Java 11 made java.net.http.HttpClient standard (it was an incubator module in Java 9 and 10).

Does Java HttpClient support HTTP/2?

Yes. It uses HTTP/2 by default when the server supports it and falls back to HTTP/1.1; you can force a version with .version(HttpClient.Version.HTTP_1_1).

Should I use HttpClient or REST Assured for API tests?

REST Assured for test suites, because of its fluent assertions and JSON path support; HttpClient for small utilities where you don't want an extra dependency.