Jetty, websocket, java.lang.RuntimeException: Cannot load platform configurator

I try to get http session in Endpoint. I followed this recomendations https://stackoverflow.com/a/17994303 . Thats why I did:

public class MyConfigurator extends ServerEndpointConfig.Configurator
{
    @Override
    public void modifyHandshake(ServerEndpointConfig config, 
                                HandshakeRequest request, 
                                HandshakeResponse response)
    {
        HttpSession httpSession = (HttpSession)request.getHttpSession();
        config.getUserProperties().put(HttpSession.class.getName(),httpSession);
    }
}

and

@ServerEndpoint(value = "/foo", configurator = MyConfigurator.class)
public class MyEndpoint {

    private Session wsSession;

    private HttpSession httpSession;


    @OnOpen
    public void open(final Session session,EndpointConfig config) {
        this.wsSession=session;
        this.httpSession = (HttpSession) config.getUserProperties().get(HttpSession.class.getName());
    }
}

And this is what I get

java.lang.RuntimeException: Cannot load platform configurator
    at javax.websocket.server.ServerEndpointConfig$Configurator.fetchContainerDefaultConfigurator(ServerEndpointConfig.java:123)
    at javax.websocket.server.ServerEndpointConfig$Configurator.getContainerDefaultConfigurator(ServerEndpointConfig.java:128)
    at javax.websocket.server.ServerEndpointConfig$Configurator.checkOrigin(ServerEndpointConfig.java:192)
    at org.eclipse.jetty.websocket.jsr356.server.JsrCreator.createWebSocket(JsrCreator.java:88)
    at org.eclipse.jetty.websocket.server.WebSocketServerFactory.acceptWebSocket(WebSocketServerFactory.java:187)
    at org.eclipse.jetty.websocket.server.WebSocketUpgradeFilter.doFilter(WebSocketUpgradeFilter.java:207)
    at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1676)
    at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:581)
    at org.ops4j.pax.web.service.jetty.internal.HttpServiceServletHandler.doHandle(HttpServiceServletHandler.java:70)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:143)
    at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:548)
    at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:226)
    at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1180)
    at org.ops4j.pax.web.service.jetty.internal.HttpServiceContext.doHandle(HttpServiceContext.java:276)
    at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:511)
    at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:185)
    at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1112)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141)
    at org.ops4j.pax.web.service.jetty.internal.JettyServerHandlerCollection.handle(JettyServerHandlerCollection.java:80)
    at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:134)
    at org.eclipse.jetty.server.Server.handle(Server.java:524)
    at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:319)
    at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:253)
    at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:273)
    at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:95)
    at org.eclipse.jetty.io.SelectChannelEndPoint$2.run(SelectChannelEndPoint.java:93)
    at org.eclipse.jetty.util.thread.strategy.ExecuteProduceConsume.executeProduceConsume(ExecuteProduceConsume.java:303)
    at org.eclipse.jetty.util.thread.strategy.ExecuteProduceConsume.produceConsume(ExecuteProduceConsume.java:148)
    at org.eclipse.jetty.util.thread.strategy.ExecuteProduceConsume.run(ExecuteProduceConsume.java:136)
    at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:671)
    at org.eclipse.jetty.util.thread.QueuedThreadPool$2.run(QueuedThreadPool.java:589)
    at java.lang.Thread.run(Thread.java:745)

I use osgi, jetty 9.3.11 and pax-web 6.0.0.

The problem is that the javax.websocket-api jar is not set up for using the ServiceLoader mechanism in osgi so it can find custom Configurator instances.

In order for that to work in osgi, the manifest in the javax.websocket-api jar would need to have these lines:

Require-Capability: osgi.serviceloader;filter:="(osgi.serviceloader=javax.websocket.server.ServerEndpointConfig.Configurator)";resolution:=optional;cardin
 ality:=multiple,osgi.extender;filter:="(osgi.extender=osgi.serviceloa
 der.processor)"

So as it does NOT have those lines, you are going to need to add another bundle with a manifest with those lines in it and that declares itself as a fragment for the javax.websocket-api bundle.

If you're using maven, the lines you'd need in a pom are something like:

      <plugin>
        <groupId>org.apache.felix</groupId>
        <artifactId>maven-bundle-plugin</artifactId>
        <configuration>
            <instructions>
              <Bundle-SymbolicName>${bundle-symbolic-name};singleton:=true</Bundle-SymbolicName>
              <Bundle-Name>OSGi Websocket API Fragment</Bundle-Name>
              <Fragment-Host>javax.websocket-api</Fragment-Host>
            <Require-Capability>osgi.serviceloader; filter:="(osgi.serviceloader=)javax.websocket.server.ServerEndpointConfig.Configurator";resolution:=optional;cardinality:=multiple, osgi.extender; filter:="(osgi.extender=osgi.serviceloader.processor)"</Require-Capability>
            </instructions>
        </configuration>
      </plugin>