用java自己写一个demo,接收http请求并响应,返回的响应用json格式

Sure, here's a sample Java code that can receive an HTTP request and respond with a JSON-encoded response:

import java.io.IOException;
import java.io.OutputStream;
import java.net.InetSocketAddress;

import com.sun.net.httpserver.HttpExchange;
import com.sun.net.httpserver.HttpHandler;
import com.sun.net.httpserver.HttpServer;
import org.json.JSONException;
import org.json.JSONObject;

public class DemoServer {

    public static void main(String[] args) throws Exception {
        HttpServer server = HttpServer.create(new InetSocketAddress(8080), 0);
        server.createContext("/demo", new MyHandler());
        server.setExecutor(null); // creates a default executor
        server.start();
    }

    static class MyHandler implements HttpHandler {
        @Override
        public void handle(HttpExchange t) throws IOException {
            String response = "";
            int status = 200;

            try {
                // Process request
                String query = t.getRequestURI().getQuery();

                if (query != null && !query.isEmpty()) {
                    // Parse query parameters
                    String[] params = query.split("&");
                    int value = 0;
                    for (String param : params) {
                        String[] keyValue = param.split("=");
                        if (keyValue[0].equals("value")) {
                            value = Integer.parseInt(keyValue[1]);
                        }
                    }

                    // Generate response
                    JSONObject json = new JSONObject();
                    json.put("result", value * 2);
                    response = json.toString();
                }
            } catch (JSONException e) {
                e.printStackTrace();
                response = "Unexpected error";
                status = 500;
            }

            // Send response
            t.getResponseHeaders().add("Content-Type", "application/json");
            t.sendResponseHeaders(status, response.length());
            OutputStream os = t.getResponseBody();
            os.write(response.getBytes());
            os.close();
        }
    }

}

This code sets up an HTTP server that listens to port 8080 and has one endpoint "/demo". When a GET request is made to this endpoint with a query parameter named "value", the server responds with a JSON-encoded message that has a "result" field with the double of the value passed in the query. For example, a request to "http://localhost:8080/demo?value=3" will result in a response of '{"result": 6}'.