java - In the program to create a simple websocket, where is the onOpen method being called? -

i found code create simple websocket connection. in main function constructor websocketclientendpoint being called , don't see call onopen function inside constructor. in output, "opening websocket" printed specified in onopen function. can please tell me call onopen function happening?

testapp.java:

package testapp;  import java.net.uri; import java.net.urisyntaxexception;  public class testapp {  public static void main(string[] args) {     try {         // open websocket         final websocketclientendpoint clientendpoint = new websocketclientendpoint(new uri("wss://real.okcoin.cn:10440/websocket/okcoinapi"));          // add listener         clientendpoint.addmessagehandler(new websocketclientendpoint.messagehandler() {             public void handlemessage(string message) {                 system.out.println(message);             }         });          // send message websocket         clientendpoint.sendmessage("{'event':'addchannel','channel':'ok_btccny_ticker'}");          // wait 5 seconds messages websocket         thread.sleep(5000);      } catch (interruptedexception ex) {         system.err.println("interruptedexception exception: " + ex.getmessage());     } catch (urisyntaxexception ex) {         system.err.println("urisyntaxexception exception: " + ex.getmessage());     } } 

}

websocketclientendpoint.java

package testapp;  import java.net.uri; import javax.websocket.clientendpoint; import javax.websocket.closereason; import javax.websocket.containerprovider; import javax.websocket.onclose; import javax.websocket.onmessage; import javax.websocket.onopen; import javax.websocket.session; import javax.websocket.websocketcontainer;   /**  * chatserver client  *  * @author jiji_sasidharan  */ @clientendpoint public class websocketclientendpoint {  session usersession = null; private messagehandler messagehandler;  public websocketclientendpoint(uri endpointuri) {     try {         websocketcontainer container = containerprovider.getwebsocketcontainer();         container.connecttoserver(this, endpointuri);     } catch (exception e) {         throw new runtimeexception(e);     } }  /**  * callback hook connection open events.  *  * @param usersession usersession opened.  */ @onopen public void onopen(session usersession) {     system.out.println("opening websocket");     this.usersession = usersession; }  /**  * callback hook connection close events.  *  * @param usersession usersession getting closed.  * @param reason reason connection close  */ @onclose public void onclose(session usersession, closereason reason) {     system.out.println("closing websocket");     this.usersession = null; }  /**  * callback hook message events. method invoked when client send message.  *  * @param message text message  */ @onmessage public void onmessage(string message) {     if (this.messagehandler != null) {         this.messagehandler.handlemessage(message);     } }  /**  * register message handler  *  * @param message  */ public void addmessagehandler(messagehandler msghandler) {     this.messagehandler = msghandler; }  /**  * send message.  *  * @param user  * @param message  */ public void sendmessage(string message) {     this.usersession.getasyncremote().sendtext(message); }  /**  * message handler.  *  * @author jiji_sasidharan  */ public static interface messagehandler {      public void handlemessage(string message); } } 

you have read how annotations works understand this.the @onopen annotation. @onopen allows intercept creation of new session.

the annotation type onopen

@retention(value=runtime)
@target(value=method)
public @interface onopen

this method level annotation can used decorate java method wishes called when new web socket session open.

the method may take following parameters:-

optional session parameter
optional endpointconfig parameter
0 n string parameters annotated pathparam annotation.

the parameters may appear in order.