How to Create a Simple HTTP Server Using Java?

Question

What is the simplest method to create an HTTP server in Java, specifically for handling GET and POST requests without an application server?

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

public class SimpleHttpServer {
    public static void main(String[] args) throws IOException {
        HttpServer server = HttpServer.create(new InetSocketAddress(8080), 0);
        server.createContext("/", new MyHandler());
        server.setExecutor(null);
        server.start();
        System.out.println("Server started on port 8080");
    }

    static class MyHandler implements HttpHandler {
        public void handle(HttpExchange exchange) throws IOException {
            String response;
            if (exchange.getRequestMethod().equalsIgnoreCase("GET")) {
                response = "This is a response to GET request";
            } else if (exchange.getRequestMethod().equalsIgnoreCase("POST")) {
                response = "This is a response to POST request";
            } else {
                response = "Method not supported";
            }
            exchange.sendResponseHeaders(200, response.length());
            OutputStream os = exchange.getResponseBody();
            os.write(response.getBytes());
            os.close();
        }
    }
}

Answer

Creating a simple HTTP server in Java can be straightforward, especially with the Built-in `HttpServer` class available in the `com.sun.net.httpserver` package. This implementation allows you to respond to both GET and POST requests without the need for a full-fledged application server.

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

public class SimpleHttpServer {
    public static void main(String[] args) throws IOException {
        HttpServer server = HttpServer.create(new InetSocketAddress(8080), 0);
        server.createContext("/", new MyHandler());
        server.setExecutor(null);
        server.start();
        System.out.println("Server started on port 8080");
    }

    static class MyHandler implements HttpHandler {
        public void handle(HttpExchange exchange) throws IOException {
            String response;
            if (exchange.getRequestMethod().equalsIgnoreCase("GET")) {
                response = "This is a response to GET request";
            } else if (exchange.getRequestMethod().equalsIgnoreCase("POST")) {
                response = "This is a response to POST request";
            } else {
                response = "Method not supported";
            }
            exchange.sendResponseHeaders(200, response.length());
            OutputStream os = exchange.getResponseBody();
            os.write(response.getBytes());
            os.close();
        }
    }
}

Causes

You need a lightweight server solution in Java.
Your project requirements specify handling of GET and POST requests.
Avoiding the overhead of a large application server.

Solutions

Utilize the `HttpServer` class from the `com.sun.net.httpserver` package to create a basic HTTP server.
Implement a custom handler to manage incoming requests and provide responses accordingly.
Ensure your server listens on a specified port and can handle multiple request types.

Common Mistakes

Mistake: Not specifying the server port correctly.

Solution: Ensure the port number is open and accessible; in the code above, it's set to 8080.

Mistake: Ignoring request method handling, leading to unhandled requests.

Solution: Always check the request method (GET or POST) before responding.

Mistake: Forgetting to set response headers appropriately.

Solution: Use `exchange.sendResponseHeaders()` to set response codes and sizes.

Helpers

HTTP server in Java
Java simple server
GET POST Java server
Java HttpServer example
Creating HTTP server Java