Java HttpClient Example: GET and POST Requests

Since Java 11 the standard library has a modern HTTP client: java.net.http.HttpClient. The example below starts a very small web server in the same program (with com.sun.net.httpserver), so it runs without internet, and then calls it with GET and POST.

Program

import com.sun.net.httpserver.HttpServer;
import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.nio.charset.StandardCharsets;

public class Main {
    public static void main(String[] args) throws Exception {
        // A tiny server for the test
        HttpServer server = HttpServer.create(new InetSocketAddress("127.0.0.1", 0), 0);
        server.createContext("/hello", exchange -> {
            byte[] body = "{\"message\":\"Hello from the server\"}".getBytes(StandardCharsets.UTF_8);
            exchange.getResponseHeaders().add("Content-Type", "application/json");
            exchange.sendResponseHeaders(200, body.length);
            exchange.getResponseBody().write(body);
            exchange.close();
        });
        server.createContext("/echo", exchange -> {
            String text = new String(exchange.getRequestBody().readAllBytes(), StandardCharsets.UTF_8);
            byte[] body = ("You sent: " + text).getBytes(StandardCharsets.UTF_8);
            exchange.sendResponseHeaders(201, body.length);
            exchange.getResponseBody().write(body);
            exchange.close();
        });
        server.start();
        int port = server.getAddress().getPort();

        // The client
        HttpClient client = HttpClient.newHttpClient();

        HttpRequest get = HttpRequest.newBuilder(URI.create("http://127.0.0.1:" + port + "/hello"))
                .GET()
                .build();
        HttpResponse<String> r1 = client.send(get, HttpResponse.BodyHandlers.ofString());
        System.out.println("GET status: " + r1.statusCode());
        System.out.println("Content-Type: " + r1.headers().firstValue("Content-Type").orElse("?"));
        System.out.println("Body: " + r1.body());

        HttpRequest post = HttpRequest.newBuilder(URI.create("http://127.0.0.1:" + port + "/echo"))
                .header("Content-Type", "text/plain")
                .POST(HttpRequest.BodyPublishers.ofString("name=Riya"))
                .build();
        HttpResponse<String> r2 = client.send(post, HttpResponse.BodyHandlers.ofString());
        System.out.println("POST status: " + r2.statusCode());
        System.out.println("Body: " + r2.body());

        server.stop(0);
    }
}

Use it with a real API

Change the address to a real one, like https://api.example.com/items. The code is the same. Always set a timeout and check the status code:

HttpClient client = HttpClient.newBuilder()
        .connectTimeout(java.time.Duration.ofSeconds(5))
        .build();

HttpRequest request = HttpRequest.newBuilder(URI.create("https://api.example.com/items"))
        .timeout(java.time.Duration.ofSeconds(10))
        .header("Accept", "application/json")
        .build();

HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());
if (response.statusCode() == 200) {
    System.out.println(response.body());
}

• client.send() waits for the answer. client.sendAsync() returns a CompletableFuture.
• The JSON text must be read with a library like Jackson or Gson. The JDK has no JSON parser.

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