**Course Title:** Comprehensive Java Programming: From Basics to Advanced Concepts **Section Title:** Web Development with Java **Topic:** Understanding the basics of HTTP and handling requests/responses **Introduction** In the previous topics, we explored the fundamentals of Java and its ecosystem. Now, we'll delve into web development with Java, starting with the basics of HTTP and handling requests/responses. Understanding HTTP is crucial for building robust web applications, and in this topic, we'll cover the fundamentals of HTTP, its architecture, and how to handle requests/responses in Java. **Understanding HTTP** HTTP (Hypertext Transfer Protocol) is an application-layer protocol that governs the communication between a client (e.g., web browser) and a server (e.g., web server). HTTP is a request-response protocol, meaning a client sends a request to the server, and the server responds with the requested data. Here are the key aspects of HTTP: * **HTTP Methods**: HTTP defines several methods, including: * GET: Retrieves data from the server * POST: Sends data to the server to create a new resource * PUT: Updates an existing resource on the server * DELETE: Deletes a resource from the server * **HTTP Status Codes**: HTTP status codes indicate the outcome of a request. Common status codes include: * 200 OK: Request successful * 404 Not Found: Requested resource not found * 500 Internal Server Error: Server error occurred * **HTTP Request Headers**: Request headers provide additional information about the request, such as the requested resource, HTTP method, and client information. * **HTTP Response Headers**: Response headers provide additional information about the response, such as the response status code, content type, and server information. **Handling Requests and Responses in Java** In Java, you can handle HTTP requests and responses using various libraries and frameworks. One popular library is the `java.net` package, which provides classes for working with HTTP connections. Here's a simple example of using the `java.net` package to send an HTTP GET request: ```java import java.net.*; import java.io.*; public class HttpRequestExample { public static void main(String[] args) throws Exception { URL url = new URL("http://example.com"); HttpURLConnection connection = (HttpURLConnection) url.openConnection(); connection.setRequestMethod("GET"); int statusCode = connection.getResponseCode(); if (statusCode == 200) { BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream())); String line; while ((line = reader.readLine()) != null) { System.out.println(line); } } else { System.out.println("Error: " + statusCode); } } } ``` **Using HttpClient** Java 11 introduced the `java.net.http.HttpClient` class, which provides a more convenient and efficient way to work with HTTP requests. Here's an example of using `HttpClient` to send an HTTP GET request: ```java import java.net.http.*; import java.net.*; public class HttpClientExample { public static void main(String[] args) throws Exception { HttpClient client = HttpClient.newHttpClient(); HttpRequest request = HttpRequest.newBuilder() .uri(URI.create("http://example.com")) .GET() .build(); client.sendAsync(request, HttpResponse.BodyHandlers.ofString()) .thenApply(HttpResponse::body) .thenAccept(System.out::println) .join(); } } ``` **Conclusion** In this topic, we explored the basics of HTTP and how to handle requests/responses in Java using the `java.net` package and `HttpClient`. Understanding HTTP is essential for building robust web applications, and we'll build upon this knowledge in the next topic, where we'll explore building RESTful services using Spring Boot. **Practice and Exercise** 1. Use the `java.net` package to send an HTTP POST request to a server with a JSON payload. 2. Use `HttpClient` to send an HTTP DELETE request to a server. **Additional Resources** * [RFC 7230: HTTP/1.1 Message Syntax and Routing](https://datatracker.ietf.org/doc/html/rfc7230) * [Java API Documentation: java.net](https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/net/package-summary.html) * [Java API Documentation: java.net.http](https://docs.oracle.com/en/java/javase/17/docs/api/java.net.http/java/net/http/package-summary.html) Do you have any questions or need further clarification on this topic? Please leave a comment or ask for help.

import java.net.*;
import java.io.*;

public class HttpRequestExample {
    public static void main(String[] args) throws Exception {
        URL url = new URL("http://example.com");
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();
        connection.setRequestMethod("GET");

        int statusCode = connection.getResponseCode();
        if (statusCode == 200) {
            BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
            String line;
            while ((line = reader.readLine()) != null) {
                System.out.println(line);
            }
        } else {
            System.out.println("Error: " + statusCode);
        }
    }
}

import java.net.http.*;
import java.net.*;

public class HttpClientExample {
    public static void main(String[] args) throws Exception {
        HttpClient client = HttpClient.newHttpClient();
        HttpRequest request = HttpRequest.newBuilder()
                .uri(URI.create("http://example.com"))
                .GET()
                .build();

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