Fetching JSON from an API using HttpClient

1. HttpClient (Introduced in Java 11)

HttpClient is a modern API for HTTP communication that was introduced in Java 11. It brings several improvements over the older HttpURLConnection:

Key Advantages of HttpClient

• Asynchronous and Synchronous Support:

  • HttpClient supports both synchronous (blocking) and asynchronous (non-blocking) requests. This is a major improvement over HttpURLConnection, allowing for better performance in applications where network latency or server response times can be variable.

  • With asynchronous requests, the application can continue processing other tasks while waiting for a response, making it more efficient for handling concurrent HTTP requests.

• Cleaner, More Intuitive API:
  • The HttpClient API is much easier to use, with less boilerplate code. It provides a builder pattern to configure the HTTP client and requests in a fluent and readable way.
• Built-in Support for HTTP/2 and WebSockets:
  • HttpClient has native support for HTTP/2, which improves performance by allowing multiplexed requests, header compression, and better resource management.
  • It also supports WebSockets, which allows real-time, bidirectional communication between the client and server.
• Timeouts and Redirection:
  • HttpClient provides easy-to-configure options for setting timeouts and handling redirections automatically, reducing the complexity involved in managing these aspects manually.
• Built-in Cookie and Authentication Support:
  • HttpClient supports managing cookies, proxies, and authentication mechanisms (such as Basic Authentication) out of the box.
• Immutable and Thread-Safe:
  • HttpClient instances are immutable and thread-safe, meaning they can be safely shared between threads, making them ideal for use in multi-threaded applications.

Example of HttpClient

import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;

public class HttpClientExample {
    public static void main(String[] args) {
        try {
            // Create an HttpClient instance
            HttpClient client = HttpClient.newHttpClient();

            // Create a request
            HttpRequest request = HttpRequest.newBuilder()
                    .uri(new URI("https://vejr.eu/api.php?location=Roskilde&degree=C"))
                    .GET()
                    .build();

            // Send the request and get the response
            HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());

            // Check the status code and print the response
            if (response.statusCode() == 200) {
                System.out.println(response.body());
            } else {
                System.out.println("GET request failed. Status code: " + response.statusCode());
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Async Example:

import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.util.concurrent.CompletableFuture;

public class AsyncHttpClientExample {
    public static void main(String[] args) {
        HttpClient client = HttpClient.newHttpClient();

        HttpRequest request = HttpRequest.newBuilder()
                .uri(URI.create("https://vejr.eu/api.php?location=Roskilde&degree=C"))
                .build();

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

        // Handle the async response
        response.thenAccept(res -> {
            if (res.statusCode() == 200) {
                System.out.println(res.body());
            } else {
                System.out.println("Request failed. Status code: " + res.statusCode());
            }
        }).join(); // Ensures the main thread waits for completion
    }
}

Comparison: HttpURLConnection vs. HttpClient

Feature	HttpURLConnection	HttpClient (Java 11+)
Asynchronous Support	No	Yes (non-blocking requests)
Synchronous Support	Yes	Yes
HTTP/2 Support	No	Yes
WebSocket Support	No	Yes
Boilerplate Code	High	Low (fluent, cleaner API)
Cookie Management	Manual	Automatic (built-in support)
Authentication Support	Manual (or third-party libraries)	Built-in support for Basic Auth, etc.
Timeout and Redirect Handling	Manual	Easy, with built-in methods
Thread Safety	Limited	HttpClient is thread-safe

Conclusion

HttpClient offers a much cleaner, modern, and feature-rich API compared to the older HttpURLConnection. It simplifies HTTP communication in Java by reducing boilerplate code, supporting both synchronous and asynchronous operations, and offering native support for HTTP/2 and WebSockets. These improvements make it the preferred choice for building HTTP clients in Java 11 and beyond.