Java Built-in HTTP Server

import com.sun.net.httpserver.*;
import java.io.*;
import java.net.InetSocketAddress;
import java.nio.charset.StandardCharsets;
import java.util.Map;
import java.util.concurrent.Executors;

public class SimpleHttpServer {

    public static void main(String[] args) throws IOException {
        HttpServer server = HttpServer.create(new InetSocketAddress(8080), 0);
        server.setExecutor(Executors.newFixedThreadPool(10));

        // JSON endpoint
        server.createContext("/api/hello", exchange -> {
            if (!"GET".equals(exchange.getRequestMethod())) {
                sendResponse(exchange, 405, "{\"error\": \"Method not allowed\"}");
                return;
            }
            String name = getQueryParam(exchange, "name", "World");
            String json = "{\"message\": \"Hello, " + name + "!\"}"; // Use a JSON lib in production
            exchange.getResponseHeaders().set("Content-Type", "application/json");
            sendResponse(exchange, 200, json);
        });

        // POST endpoint — read body
        server.createContext("/api/echo", exchange -> {
            if (!"POST".equals(exchange.getRequestMethod())) {
                sendResponse(exchange, 405, "POST only");
                return;
            }
            String body = new String(exchange.getRequestBody().readAllBytes(), StandardCharsets.UTF_8);
            exchange.getResponseHeaders().set("Content-Type", "text/plain");
            sendResponse(exchange, 200, "Echo: " + body);
        });

        // Health check
        server.createContext("/health", exchange -> {
            sendResponse(exchange, 200, "{\"status\": \"UP\"}");
        });

        server.start();
        System.out.println("Server running on http://localhost:8080");
    }

    static void sendResponse(HttpExchange exchange, int status, String body)
            throws IOException {
        byte[] bytes = body.getBytes(StandardCharsets.UTF_8);
        exchange.sendResponseHeaders(status, bytes.length);
        try (OutputStream os = exchange.getResponseBody()) {
            os.write(bytes);
        }
    }

    static String getQueryParam(HttpExchange exchange, String key, String defaultVal) {
        String query = exchange.getRequestURI().getQuery();
        if (query == null) return defaultVal;
        for (String param : query.split("&")) {
            String[] kv = param.split("=", 2);
            if (kv[0].equals(key) && kv.length > 1) return kv[1];
        }
        return defaultVal;
    }
}