Advanced Java Network Programming: Basics of HTTP Protocol and Web Development

In this article, we will delve into the HTTP protocol and learn how to perform simple web development using Java. As a basic user, you will understand the fundamental concepts of HTTP and how to create a simple HTTP server using Java.

What is the HTTP Protocol?

HTTP (Hypertext Transfer Protocol) is an application layer protocol used for transferring web pages from a web server to a client (usually a browser). When you enter a URL in the browser, it sends a request to the server via HTTP and retrieves the corresponding data.

HTTP Requests and Responses

A complete HTTP communication process generally consists of two main parts: the request and the response.

HTTP Request:

The client sends data to the server, requesting certain resources.
It includes the request line, request headers, and request body.

HTTP Response:

After processing the request, the server returns data to the client.
It includes the status line, response headers, and response body.

Common HTTP Methods

GET: Requests the specified page information and returns the entity body.
POST: Submits data to the specified resource, used for submitting forms or uploading files.
PUT: Updates the information of the specified resource.
DELETE: Deletes the specified resource.

Creating a Simple HTTP Server with Java

Next, we will implement a simple HttpServer that can handle GET and POST requests and return the corresponding data. In this example, we will use Java’s built-in com.sun.net.httpserver.HttpServer class to build our HttpServer.

Step 1: Add Necessary Dependencies

If you are using Maven to build your project, you can directly use the built-in library of the JDK without additional dependencies. Ensure that your JDK version supports the HttpServer API (JDK 7 and above).

Step 2: Write the Code

Below is an example code for creating a basic HTTP server:

import java.io.IOException;
import java.io.OutputStream;
import java.net.InetSocketAddress;
import com.sun.net.httpserver.HttpServer;
import com.sun.net.httpserver.HttpHandler;
import com.sun.net.httpserver.HttpExchange;

public class SimpleHttpServer {
    public static void main(String[] args) throws IOException {        // Create an instance of HttpServer, binding to the specified address and port        HttpServer server = HttpServer.create(new InetSocketAddress(8080), 0);
        // Register context, i.e., URL path "/"        server.createContext("/", new MyHandler());
        // Start the service        server.setExecutor(null);         System.out.println("Starting the server on port 8080...");        server.start();    }
    static class MyHandler implements HttpHandler {        @Override        public void handle(HttpExchange exchange) throws IOException {            String response = "Hello, World!"; // Response message
            // Set response header information            exchange.sendResponseHeaders(200, response.getBytes().length);
            OutputStream os = exchange.getResponseBody();            os.write(response.getBytes()); // Write to output stream            os.close(); // Close stream        }    }
}

Explanation of the Above Code:

Create Server: We call the HttpServer.create() method and bind it to the local address and desired port, here we choose port 8080.
Register Context: Use createContext() to register the root path / with the custom handler MyHandler. Whenever there is access to this path, the logic in this handler will be invoked.
Handle Request/Response:

In the handle method, we set the response message to “Hello, World!” and send the corresponding status code 200 indicating the request was successfully completed, finally writing this message to the output stream and closing it.

Step 3: Run the Service and Test

Place the above code in the main class of your project and run it. The console will prompt “Starting the server on port 8080…” indicating that the service has started.
Open your browser or use tools like Postman to access http://localhost:8080, you should see the message “Hello, World!” displayed. If you can access it successfully, it means your small HTTP server is working properly!

Conclusion and Outlook

This article introduced the basics of network programming in Java, including an introduction to the HTTP protocol and the implementation of a simple form of a small web server in Java. With this knowledge, you can further explore frameworks like Spring Boot to develop complex web applications more efficiently, leveraging the rich features provided by frameworks to quickly build robust and maintainable websites or API interfaces and other modern product directions. I hope readers can continue to learn deeply and continuously improve their skills in practical development.