networking5HttpClient

1package pkg10networking;2 3import com.sun.net.httpserver.HttpServer;4import java.net.InetSocketAddress;5import java.net.URI;6import java.net.http.HttpClient;7import java.net.http.HttpRequest;8import java.net.http.HttpResponse;9import java.nio.charset.StandardCharsets;10import java.time.Duration;11 12/*13 * networking5HttpClient.java14 * --------------------------15 * The modern HTTP client: java.net.http.HttpClient (Java 11+).16 *17 * DEFINITION:18 *   HttpClient is the standard, fluent, HTTP/2-capable client. It supports19 *   sync and async calls, timeouts, redirects, and body handlers. This demo20 *   talks to a local server so it runs offline.21 *22 * KEY POINTS:23 *   - Build once (HttpClient.newBuilder()), reuse for many requests.24 *   - HttpRequest is immutable; choose GET/POST and a BodyPublisher.25 *   - BodyHandlers.ofString() turns the response body into a String.26 *   - sendAsync() returns a CompletableFuture for non-blocking calls.27 */28public class networking5HttpClient {29 30    public static void main(String[] args) throws Exception {31        // Local echo-ish server: GET returns text, POST echoes the request body32        HttpServer server = HttpServer.create(new InetSocketAddress("127.0.0.1", 0), 0);33        server.createContext("/api", ex -> {34            String method = ex.getRequestMethod();35            byte[] reqBody = ex.getRequestBody().readAllBytes();36            String reply = "GET".equals(method)37                    ? "{\"message\":\"hello\"}"38                    : "{\"echo\":\"" + new String(reqBody, StandardCharsets.UTF_8) + "\"}";39            byte[] out = reply.getBytes(StandardCharsets.UTF_8);40            ex.getResponseHeaders().add("Content-Type", "application/json");41            ex.sendResponseHeaders(200, out.length);42            ex.getResponseBody().write(out);43            ex.close();44        });45        server.start();46        String base = "http://127.0.0.1:" + server.getAddress().getPort() + "/api";47 48        HttpClient client = HttpClient.newBuilder()49                .connectTimeout(Duration.ofSeconds(2))50                .version(HttpClient.Version.HTTP_1_1)51                .build();52 53        // 1) GET54        HttpRequest get = HttpRequest.newBuilder(URI.create(base))55                .header("Accept", "application/json")56                .GET()57                .build();58        HttpResponse<String> getResp = client.send(get, HttpResponse.BodyHandlers.ofString());59        System.out.println("GET  status: " + getResp.statusCode());60        System.out.println("GET  body  : " + getResp.body());61 62        // 2) POST with a body63        HttpRequest post = HttpRequest.newBuilder(URI.create(base))64                .header("Content-Type", "application/json")65                .POST(HttpRequest.BodyPublishers.ofString("{\"name\":\"Ada\"}"))66                .build();67        HttpResponse<String> postResp = client.send(post, HttpResponse.BodyHandlers.ofString());68        System.out.println("\nPOST status: " + postResp.statusCode());69        System.out.println("POST body  : " + postResp.body());70 71        // 3) Async GET (non-blocking) — join just to print in this demo72        client.sendAsync(get, HttpResponse.BodyHandlers.ofString())73              .thenApply(HttpResponse::body)74              .thenAccept(b -> System.out.println("\nASYNC body : " + b))75              .join();76 77        server.stop(0);78    }79}