15.4 HTTP Client API Explained

The HTTP Client API, introduced in Java SE 11, is a modern, flexible, and efficient way to handle HTTP requests and responses. It supports both HTTP/1.1 and HTTP/2 protocols, making it a powerful tool for networking in Java applications.

Key Concepts

1. HttpClient Class

The HttpClient class is the main entry point for sending HTTP requests and receiving responses. It provides methods to configure and execute HTTP requests.

Example

        HttpClient client = HttpClient.newHttpClient();
    

2. HttpRequest Class

The HttpRequest class represents an HTTP request. It allows you to specify the request method, URI, headers, and body.

Example

        HttpRequest request = HttpRequest.newBuilder()
            .uri(URI.create("https://example.com"))
            .GET()
            .build();
    

3. HttpResponse Class

The HttpResponse class represents an HTTP response. It provides access to the response status code, headers, and body.

Example

        HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());
        int statusCode = response.statusCode();
        String body = response.body();
    

4. BodyHandlers and BodyPublishers

The BodyHandlers and BodyPublishers interfaces provide methods to handle the request and response bodies. They support various data types, including strings, byte arrays, and files.

Example

        HttpRequest request = HttpRequest.newBuilder()
            .uri(URI.create("https://example.com"))
            .POST(HttpRequest.BodyPublishers.ofString("request body"))
            .build();
        
        HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());
    

5. Asynchronous Requests

The HTTP Client API supports asynchronous requests using the sendAsync method. This allows you to perform non-blocking HTTP requests and handle responses asynchronously.

Example

        CompletableFuture<HttpResponse<String>> future = client.sendAsync(request, HttpResponse.BodyHandlers.ofString());
        future.thenAccept(response -> {
            System.out.println(response.body());
        });
    

Examples and Analogies

Think of the HTTP Client API as a modern communication tool that allows your application to interact with other services over the internet. For instance, sending an HTTP request is like placing an order at a restaurant, where you specify what you want (request method, URI, headers, and body). Receiving a response is like getting your order delivered (response status code, headers, and body).

For example, if you are building a web application that needs to fetch data from an external API, the HTTP Client API allows you to make these requests efficiently and handle the responses gracefully. The asynchronous capabilities are like having a delivery service that notifies you when your order is ready, allowing you to continue with other tasks until then.

By mastering the HTTP Client API, you can create more responsive and efficient networking applications in Java SE 11, making your code more robust and maintainable.