Unable to make my Http Server multithreaded? I'

Question

I have a following code snippet to make my HttpServer a multithreaded one,but its still working as single threaded.Can you please help me out? I'm using Java HttpServer API :

// Bind to port 8083
httpServer = HttpServer.create(new InetSocketAddress(HTTP_PORT), 0);

// Adding '/send' context
httpServer.createContext("/send", new SendHandler());

ExecutorService executor = Executors.newCachedThreadPool();
httpServer.setExecutor(executor);

// Start the server
httpServer.start();

Full Java Class :

public class GCMMockServer {

    static HttpServer httpServer;
    static final int HTTP_PORT = 8083;

    public static void main(String[] args) {
        GCMMockServer.start();
    }

    public static void start() {
        try {
            // Bind to port 8083
            httpServer = HttpServer.create(new InetSocketAddress(HTTP_PORT), 0);

            // Adding '/send' context
            httpServer.createContext("/send", new SendHandler());

            ExecutorService executor = Executors.newCachedThreadPool();
            httpServer.setExecutor(executor);

            // Start the server
            httpServer.start();

            System.out.println("GCM Mock Server started at (localhost,8083)");
        } catch (IOException ex) {
            Logger.getLogger(GCMMockServer.class.getName()).log(Level.SEVERE,
                    null, ex);
        }
    }

    public static void stop() {
        httpServer.stop(5);
    }

    // Handler for '/send' context
    static class SendHandler implements HttpHandler {

        @Override
        public void handle(HttpExchange he) throws IOException {
            System.out.println("Serving the request");

            // Serve for POST requests only
            if (he.getRequestMethod().equalsIgnoreCase("POST")) {

                try {
                    // REQUEST Headers
                    Headers requestHeaders = he.getRequestHeaders();
                    Set<Map.Entry<String, List<String>>> entries = requestHeaders
                            .entrySet();

                    System.out.println("Inside POST method");

                    int contentLength = Integer.parseInt(requestHeaders
                            .getFirst("Content-length"));
                    List<String> contentTypes = null;

                    for (Iterator<Entry<String, List<String>>> iterator = entries
                            .iterator(); iterator.hasNext();) {
                        Entry<String, List<String>> entry = iterator.next();
                        String key = entry.getKey();
                        System.out.println("Key : " + key + ", values : ");
                        if (key.equalsIgnoreCase("Content-type")) {
                            contentTypes = entry.getValue();
                        }
                        for (Iterator<String> iterator2 = entry.getValue()
                                .iterator(); iterator2.hasNext();) {
                            String value = iterator2.next();
                            System.out.println("-----------" + value);
                        }
                    }

                    System.out.println("Content length : " + contentLength);

                    // REQUEST Body
                    InputStream is = he.getRequestBody();

                    if (contentTypes.contains("application/json")) {

                        InputStreamReader isr = new InputStreamReader(is,
                                "utf-8");
                        BufferedReader br = new BufferedReader(isr);

                        // From now on, the right way of moving from bytes to
                        // utf-8 characters:

                        int b;
                        StringBuilder buf = new StringBuilder(512);
                        while ((b = br.read()) != -1) {
                            buf.append((char) b);
                        }

                        JSONObject req = new JSONObject(buf.toString());
                        System.out.println("Request body : " + req);
                        String to = (String) req.get("to");
                        String message = (String) ((JSONObject) req.get("data"))
                                .get("message");
                        System.out.println("Request message : " + message
                                + ", to : " + to);
                    }

                    // RESPONSE Headers
                    Headers responseHeaders = he.getResponseHeaders();
                    System.out.println("Response Headers : "
                            + responseHeaders.toString());

                    String response = "Message received";
                    // Send RESPONSE Headers
                    he.sendResponseHeaders(HttpURLConnection.HTTP_OK,
                            response.length());

                    // RESPONSE Body
                    OutputStream os = he.getResponseBody();

                    os.write(response.getBytes());

                    is.close();
                    os.flush();
                    os.close();
                    he.close();

                } catch (Exception e) {
                    e.printStackTrace();
                }
            } else if (he.getRequestMethod().equalsIgnoreCase("GET")) {
                System.out.println("Nothing to serve in GET request type");

                // RESPONSE Headers
                Headers responseHeaders = he.getResponseHeaders();
                String response = "Hi This is Sandeep";
                System.out.println("Response Headers : "
                        + responseHeaders.toString());

                // Send RESPONSE Headers
                he.sendResponseHeaders(HttpURLConnection.HTTP_OK,
                        response.length());

                // RESPONSE Body
                OutputStream os = he.getResponseBody();
                OutputStreamWriter osw = new OutputStreamWriter(os);

                osw.write(response);

                // is.close();
                osw.close();
                os.close();
                he.close();
            }

        }
    }
}

Answer 1

Consider changing the start of your handle method:

 @Override
 public void handle(HttpExchange he) throws IOException {
    System.out.println("Serving the request from Thread "
          + Thread.currentThread().getName() + " / " 
          + Thread.currentThread().getId());
    try {
      Thread.sleep(5000);
    } catch(InterruptedException ie) {
       ie.printStackTrace();
       return;
    }
    System.out.println("Continue request in Thread "
          + Thread.currentThread().getName() + " / " 
          + Thread.currentThread().getId());

Now start the server, open up a browser, load your url, refresh twise within 5s and watch your console log.

I have a feeling you'll be seeing multiple threads just fine.

Regarding your test:

The Test you use is single threaded (a for-loop). So there will be only one active invocation of your servlet at any one time. As the next iteration of your for loop will only start once the last one is finished, the previous thread in the executor thread pool was recycled. There simply was no need for mutlithreading based on your test.