Develop Reference

Any idea on how to implement the push-based messaging system using CoAP with Java?

I am willing to use CoAP protocol for implementing a java push-based messaging system. Particularly in such a system, a client opens just once a connection with a server (resource) and the server pushes messages (‘non-confirmable’) with a specific rate (e.g., 10 messages per second). However I did not find any existing solution to build the above system.
What I found is the pull-based messaging system. For such case, a client opens a connection with the server and after some time the client sends a GET request. Then, the server handles the request and pushes (as response) a single message to the client.
Hence, for each GET, I have a single message as response -- i.e., a two-way asynchronous interaction.
Does anybody have any idea on how to implement the push-based messaging system using CoAP? Does CoAP supports such a system?
The pull-based messaging system is implemented as follows
Server Part
public class CoapServerPartAsync extends CoapServer {
private static final int COAP_PORT = 8891;
private static int incrementor = 1;
/*
* Application entry point.
*/
public static void main(String[] args) {
try {
// create server
CoapServerPartAsync server = new CoapServerPartAsync();
// add endpoints on all IP addresses
server.addEndpoints();
server.start();
} catch (SocketException e) {
System.err.println("Failed to initialize server: " + e.getMessage());
}
}
/**
* Add endpoints listening on default CoAP port on all IP addresses of all network interfaces.
*
* #throws SocketException if network interfaces cannot be determined
*/
private void addEndpoints() throws SocketException {
InetSocketAddress bindToAddress = new InetSocketAddress("127.0.0.1", COAP_PORT);
addEndpoint(new CoapEndpoint(bindToAddress));
}
/*
* Constructor for a new Hello-World server. Here, the resources
* of the server are initialized.
*/
public CoapServerPartAsync() throws SocketException {
// provide an instance of a Hello-World resource
add(new HelloWorldResource());
}
/*
* Definition of the Hello-World Resource
*/
class HelloWorldResource extends CoapResource {
public HelloWorldResource() {
// set resource identifier
super("helloWorld");
// set display name
getAttributes().setTitle("Hello-World Resource");
}
#Override
public void handleGET(CoapExchange exchange){
// respond to the request
System.out.println("Push [Hello World!"+(incrementor)+"]");
exchange.respond("Hello World!"+(incrementor));
incrementor++;
}
}
}
Client Part
public class CoapClientPartAsync {
// static boolean getResponse = false;
public static void main(String args[]) {
CoapClient client = new CoapClient("coap://127.0.0.1:8891/helloWorld").useNONs();
while(true){
CoapObserveRelation relation = client.observe(
new CoapHandler() {
#Override public void onLoad(CoapResponse response){
String content = response.getResponseText();
System.out.println("NOTIFICATION: " + content);
}
#Override public void onError() {
System.err.println("OBSERVING FAILED (press enter to exit)");
}
});
try {
Thread.sleep(1000);
}catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}

How to know: How many requests is HttpServer-in-Vertx serving

I write a server with Vertx.
I have about 40k users. I can print every request but I don't know how to know how many current requests my server is serving
I used this class: http://vertx.io/docs/apidocs/io/vertx/core/http/HttpServer.html but this is no method to do it
Vertx is great toolkit but it can not show server status, really????
My server code:
public class MyFirstVerticle extends AbstractVerticle {
private HttpServer httpServer = null;
#Override
public void start() throws Exception {
httpServer = vertx.createHttpServer();
httpServer.requestHandler(new Handler<HttpServerRequest>() {
#Override
public void handle(HttpServerRequest request) {
String path = request.path();
System.out.println("incoming request: [" + request.remoteAddress() + "] at " + path);
}
});
httpServer.listen(9999);
}
}

Since vert.x 3.x.x http://vertx.io/docs/vertx-dropwizard-metrics is an official component of vert.x
I think what you search is this:
http://vertx.io/docs/vertx-dropwizard-metrics/java/#http-server-metrics
There are several possibilities to view the metrics
jmx http://vertx.io/docs/vertx-dropwizard-metrics/java/#jmx
http bridge for jmx http://vertx.io/docs/vertx-dropwizard-metrics/java/#_using_jolokia_and_hawtio
In our project we write periodically to a log file and send it in parallel to a graphite / grafana instance over udp

Vert.x requests are very short lived, so basing calculations solely on number of requests per second is not optimal. But, for the sake of discussion, you can achieve what you want in the following way:
public class MyFirstVerticle extends AbstractVerticle {
private HttpServer httpServer = null;
// Bad, done for the sake of simplicity
public final static AtomicInteger counter = new AtomicInteger(0);
#Override
public void start() throws Exception {
httpServer = vertx.createHttpServer();
httpServer.requestHandler(new Handler<HttpServerRequest>() {
public void handle(HttpServerRequest request) {
counter.incrementAndGet();
String path = request.path();
System.out.println("incoming request: [" + request.remoteAddress() + "] at " + path);
request.response().end();
request.endHandler(new Handler<Void>() {
#Override
public void handle(Void aVoid) {
counter.decrementAndGet();
}
});
}
});
httpServer.listen(9999);
}
}
Then to test yourself you can try something like that:
public class Main {
public static void main(String[] args) {
Vertx vertx = Vertx.vertx();
MyFirstVerticle verticle = new MyFirstVerticle();
vertx.deployVerticle(verticle);
// Very bad, but our request are very short
vertx.setPeriodic(1, new Handler<Long>() {
#Override
public void handle(Long aLong) {
// Otherwise will overflow our console
if (MyFirstVerticle.counter.intValue() > 0) {
System.out.println(MyFirstVerticle.counter.intValue());
}
}
});
}
}

Adding new resources dynamically - CoAP

Once CoAP server is started I need to add new resources dynamically. But I have to stop and start the server again in order to access new resources. I suppose adding new resources same as adding a new HTTP servlet into already started HTTP server.
Here I added source code which is used for adding dynamic resources. If I am missing anything here let me know.
private static CoapServer server;
public CoAPEventAdapter(InputEventAdapterConfiguration eventAdapterConfiguration,
Map<String, String> globalProperties) {
this.eventAdapterConfiguration = eventAdapterConfiguration;
this.globalProperties = globalProperties;
if(server == null){
server = new CoapServer();
server.start();
}
}
#Override
public void connect() {
registerDynamicEndpoint(eventAdapterConfiguration.getName());
isConnected = true;
}
private void registerDynamicEndpoint(String adapterName) {
server.stop();
server.add(new HelloWorldResource(adapterName));
server.start();
}
class HelloWorldResource extends CoapResource {
public HelloWorldResource(String resourceName) {
// set resource identifier
super(resourceName);
// set display name
getAttributes().setTitle("Hello-World Resource");
}
#Override
public void handleGET(CoapExchange exchange) {
// respond to the request
exchange.respond("Hello World!");
}
}

I've just tried to add a CoapResource dynamically:
#Override
public void handleGET(CoapExchange exchange) {
server.getRoot().add(new CoapResource("dynstatus") {
#Override
public void handleGET(CoapExchange exchange) {
System.err.println("dynstatus!!!");
}
});
And was able to call it.

Creating SockJS server with Java

I'm very new with Vert.x so excuse my newbness.
I was able to create a very simply SockJS server with Vert.x however I can't figure out how to register events/callbacks/handlers when connections are open or closed.
With JSR-356, it's drop dead simple to handle open/close connection events:
#OnOpen
public void onOpen(Session userSession) {
// Do whatever you need
}
#OnClose
public void onClose(Session userSession) {
// Do whatever you need
}
Using the SockJS support in Spring Framework 4.0 M1+, it's almost the same as JSR-356:
public class MySockJsServer extends TextWebSocketHandlerAdapter {
#Override
public void afterConnectionEstablished(WebSocketSession session) throws Exception {
// Do whatever you need
}
#Override
public void afterConnectionClosed(WebSocketSession session, CloseStatus status) throws Exception {
// Do whatever you need
}
}
For some reason I couldn't figure out how to do something so conceptually simple in Vert.x. I though Vert.x was simple ?!!
If anyone can point me in the right direction, please help.
I played around with EventBus and EventBus hooks but it didn't work. Perhaps that's the wrong approach anyhow.
I'm using Vert.x version 2.0.1
TIA

This is the answer:
HttpServer httpServer = vertx.createHttpServer();
// Create HTTP server
httpServer = httpServer.requestHandler(new Handler<HttpServerRequest>() {
#Override
public void handle(HttpServerRequest req) {
req.response().sendFile("web/" + req.path());
}
});
// Create SockJS Server
SockJSServer sockJSServer = vertx.createSockJSServer(httpServer);
sockJSServer = sockJSServer.installApp(new JsonObject().putString("prefix", "/test"), new Handler<SockJSSocket>() {
public void handle(final SockJSSocket sock) {
System.out.println("New session detected!");
// Message handler
sock.dataHandler(new Handler<Buffer>() {
public void handle(Buffer buffer) {
System.out.println("In dataHandler");
}
});
// Session end handler
sock.endHandler(new Handler<Void>() {
#Override
public void handle(Void arg) {
System.out.println("In endHandler");
}
});
}
});
httpServer.listen(8080);

tomcat websocket servlet listening port

I'm trying to write a servlet that uses org.apache.catalina.websocket.WebSocketServlet. I've found an example of websocket chat, but I can't figure out how can I specify the listening port for a websocket server (which is implemented in this servlet)? For example I need to listen for clients connection on port 11337. But how I can express this?
OK, here is the (simplified) code:
public class TestServlet extends WebSocketServlet {
private static final Logger logger = LoggerFactory.getLogger(TestServlet.class);
public TestServlet() {
logger.error("Initializing TestServlet");
}
#Override
protected StreamInbound createWebSocketInbound(String subProtocol, HttpServletRequest request) {
logger.error("New WS connection, subProtocol=" + subProtocol + ", request=" + request.getRequestURL());
return new TestConnection();
}
private class TestConnection extends MessageInbound {
#Override
protected void onBinaryMessage(ByteBuffer byteBuffer) throws IOException {
logger.error("onBinaryMessage");
}
#Override
protected void onTextMessage(CharBuffer charBuffer) throws IOException {
logger.error("onBinaryMessage: " + charBuffer);
sendMessage("Test message");
}
public void sendMessage(String message) {
WsOutbound outbound = this.getWsOutbound();
CharBuffer cb = CharBuffer.wrap(message);
try {
outbound.writeTextMessage(cb);
} catch (IOException e) {
logger.error("failed to write outbound");
}
}
}
}
I can't find where and how I can set listening port. Official websocket documentation also doesn't help much.
So I guess it can be set somewhere in servlet settings, but can't find where.
Does anyone have any ideas?

WebSocket is designed to work over HTTP protocol and so it won't have different listening port like normal TCP Socket but it use the same server port that it deployed on.
so here in your case, if you are using tomcat server than websocket may use port 8080 (if you haven't modified explicitly) for communication. You may need to override onOpen and onClose methods of MessageInbound class to get notified on Connection established and connection close. Refer below sample code for more details.
public class IncomingMessageHandler extends MessageInbound {
private WsOutbound myoutbound;
public IncomingMessageHandler() {
}
#Override
public void onOpen(WsOutbound outbound) {
logger.info("Open Client.");
this.myoutbound = outbound;
}
#Override
public void onClose(int status) {
logger.info("Close Client.");
}
/**
* Called when received plain Text Message
*/
#Override
public void onTextMessage(CharBuffer cb) throws IOException {
}
/**
* We can use this method to pass image binary data, eventually !
*/
#Override
public void onBinaryMessage(ByteBuffer bb) throws IOException {
}
public synchronized void sendTextMessage(String message) {
try {
CharBuffer buffer = CharBuffer.wrap(message);
this.getMyoutbound().writeTextMessage(buffer);
this.getMyoutbound().flush();
} catch (IOException e) {
}
}
/**
* Set timeout in milliseconds, -1 means never
*/
#Override
public int getReadTimeout() {
return -1;
}
public WsOutbound getMyoutbound() {
return myoutbound;
}
public void setMyoutbound(WsOutbound myoutbound) {
this.myoutbound = myoutbound;
}
}