HandshakeWebSocketService assumes jakarta websocket is present #33970
Description
HandshakeWebSocketService#initUpgradeStrategy does not check for the availability of relevant classes before attempting to instanciate StandardWebSocketUpgradeStrategy.
static RequestUpgradeStrategy initUpgradeStrategy() { if (tomcatWsPresent) { return new TomcatRequestUpgradeStrategy(); } else if (jettyWsPresent) { return new JettyRequestUpgradeStrategy(); } else if (undertowWsPresent) { return new UndertowRequestUpgradeStrategy(); } else if (reactorNettyPresent) { // As late as possible (Reactor Netty commonly used for WebClient) return ReactorNettyStrategyDelegate.forReactorNetty1(); } else if (reactorNetty2Present) { // As late as possible (Reactor Netty commonly used for WebClient) return ReactorNettyStrategyDelegate.forReactorNetty2(); } else { // Let's assume Jakarta WebSocket API 2.1+ return new StandardWebSocketUpgradeStrategy(); } }This breaks when you attempt to load a context without a dependency on jakarta.websocket-client-api.
It looks like it should be handled gracefully by the following code in WebFluxConfigurationSupport:
private WebSocketService initWebSocketService() { WebSocketService service = getWebSocketService(); if (service == null) { try { service = new HandshakeWebSocketService(); } catch (IllegalStateException ex) { // Don't fail, test environment perhaps service = new NoUpgradeStrategyWebSocketService(); } } return service; }but because a ClassNotFoundException is thrown instead of IllegalStateException; the context simply fails to load instead of falling back to NoUpgradeStrategyWebSocketService