09. Using WebSockets and HTTP

marzo 14, 2022

Introduction

Thanks to BalusC for the valuable information!

WebSockets enables server-client communication much more fluently than servlets! In long processes, you can inform the user of everything that is happening in time. In the servlets, you need to wait till the process has ended or use asynchronous servlets that are prune error.

Information on WebServlets can be seen on Oracle web. and better in another post from Abhishek Gupta

Here is his code but changing "javax" with "jakarta"

These files are needed:

A java WebSocket endpoint (EndPoint.java)
A Server Endpoint Config.Configurator (HttpSessionConfigurator.java)
A client WebSocket implemented in Html with javascript code (websocket.html)

EndPoint.java

package gupta;

import java.io.IOException;

//import http.SessionWrapper;
import jakarta.servlet.http.HttpSession;
import jakarta.websocket.EndpointConfig;
import jakarta.websocket.OnOpen;
import jakarta.websocket.Session;
import jakarta.websocket.server.PathParam;
import jakarta.websocket.server.ServerEndpoint;
import openadmin.model.control.MenuItem;

@ServerEndpoint(value = "/gupta/{user}", configurator = HttpSessionConfigurator.class)

public class Service {

	private EndpointConfig config;

	@OnOpen
	public void opened(@PathParam("user") String user, Session session, EndpointConfig config) throws IOException {
		this.config = config;
	}

        @OnMessage
	public void onReceipt(Session session,String message) throws IOException {
		System.out.println("===============================================================================");
		System.out.println("Got message:"+message);
		System.out.println("===============================================================================");
		session.getBasicRemote().sendText("echo 1"+message);
		session.getBasicRemote().sendText("echo 2"+message);
		session.getBasicRemote().sendText("echo 3"+message);
		
		
		//Close the connection form server
		CloseReason closeReason= new CloseReason(CloseCodes.NORMAL_CLOSURE, "It's time to close!....");
		session.close(closeReason);

        @OnMessage
	public void binaryMessage(Session session, ByteBuffer msg) {
	      System.out.println("I am sending this Binary message: " + msg.toString());
	}

	@OnMessage
	public void pongMessage(Session session, PongMessage msg) {
		System.out.println("Pong message: " + 
	    msg.getApplicationData().toString());
	}
	
	@OnClose
	public void handleClose() {
		System.out.println("Desconnected client .......!");
	}

	@OnError
	public void handleError(Throwable t) {
		t.printStackTrace();
	}

}

HttpSessionConfigurator.java

NOTE: It is important to verify that the httpSession is not null, or else when storing it in the map, an exception is thrown!!!

package gupta;

import jakarta.servlet.http.HttpSession;
import jakarta.websocket.HandshakeResponse;
import jakarta.websocket.server.HandshakeRequest;
import jakarta.websocket.server.ServerEndpointConfig;

public class HttpSessionConfigurator extends ServerEndpointConfig.Configurator {

	@Override
	public void modifyHandshake(ServerEndpointConfig config, HandshakeRequest request, HandshakeResponse response) {
		//System.out.println("modifyHandshake() Current thread " + Thread.currentThread().getName());
		
		HttpSession httpSession = (HttpSession) request.getHttpSession();
	    
		Map<String, Object> mp =config.getUserProperties();
		
		if (mp==null ) System.out.println("config.getUserProperties() is null");
		else if (httpSession==null)  System.out.println("httpSession is null");
		else mp.put("httpSession", httpSession);
	}

}

websocket.html

<!DOCTYPE html>
<html>
<head>
  <!-- jQuery -->
  <script src="http://code.jquery.com/jquery-latest.js"> </script>
  <meta charset="UTF-8"> 
  <title>websocket tutorial</title>
</head>
<body>
  <form>
    <input id="textMessage" type="text">
    <input onclick="sendMessage();" value="Send Message" type="button">
  </form>
  <br>
	
  <textarea id="messagesTextArea" rows="10" cols="50"></textarea>

  <script type="text/javascript">
    
    var webSocket =new WebSocket("ws://localhost:8080/JSP-05/gupta/ximo");  // ws://<host>:<port>/application>/<path>/<path param>
    	
    var messagesTextArea = document.getElementById("messagesTextArea");
    	
    webSocket.onopen =    function (message) { processOpen(message);};
    webSocket.onclose =   function (message) { processClose(message);};
    webSocket.onerror =   function (message) { processError(message);};
    webSocket.onmessage = function (message) { processMessage(message);};
    	
    	
    	
    function processOpen(message) {
    	messagesTextArea.value += "Server Connect...."+"\n";
    }
    	
    function processMessage(message) {
    		
    	messagesTextArea.value += "Receive From Server ==>" + message.data + "\n";
    		
    	
    function sendMessage(message) {
    	if (textMessage.value!="close") {
    		webSocket.send(textMessage.value);
    		messagesTextArea.value += "Sent to server.===>"+ textMessage.value + "\n";
    		textMessage.value="";
    	}else websocket.close();	
    }
    	
    function processClose(message) {
    	webSocket.send("client disconnected....");
    	messagesTextArea.value += "Server Disconnect...."+"\n";
    }
    	
    function processError(message) {
    		
    	messagesTextArea.value += "error...."+"\n";
    }
    
  </script>


</body>
</html>

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