make number of web-socket-workers / decoders configurable

Author: Daniel Rentsch

OCPP-J/src/main/java/eu/chargetime/ocpp/JSONConfiguration.java

@@ -37,6 +37,7 @@ public class JSONConfiguration {
   public static final String USERNAME_PARAMETER = "USERNAME";
   public static final String PASSWORD_PARAMETER = "PASSWORD";
   public static final String CONNECT_TIMEOUT_IN_MS_PARAMETER = "CONNECT_TIMEOUT_IN_MS";
+  public static final String WEBSOCKET_WORKER_COUNT = "WEBSOCKET_WORKER_COUNT";
 
   private final HashMap<String, Object> parameters = new HashMap<>();
 

OCPP-J/src/main/java/eu/chargetime/ocpp/WebSocketListener.java

@@ -48,6 +48,7 @@ of this software and associated documentation files (the "Software"), to deal
 public class WebSocketListener implements Listener {
   private static final Logger logger = LoggerFactory.getLogger(WebSocketListener.class);
 
+  private static final int DEFAULT_WEBSOCKET_WORKER_COUNT = 4;
   private static final int TIMEOUT_IN_MILLIS = 10000;
 
   private static final int OCPPJ_CP_MIN_PASSWORD_LENGTH = 16;
@@ -78,7 +79,10 @@ public WebSocketListener(ISessionFactory sessionFactory, Draft... drafts) {
   @Override
   public void open(String hostname, int port, ListenerEvents handler) {
     server =
-        new WebSocketServer(new InetSocketAddress(hostname, port), drafts) {
+        new WebSocketServer(
+                new InetSocketAddress(hostname, port),
+                configuration.getParameter(JSONConfiguration.WEBSOCKET_WORKER_COUNT, DEFAULT_WEBSOCKET_WORKER_COUNT),
+                drafts) {
           @Override
           public void onOpen(WebSocket webSocket, ClientHandshake clientHandshake) {
             logger.debug(