WebSocketMessageBrokerStats has null stats for stompSubProtocolHandler since 5.3.2

[countableSet]

Since upgrading spring-websockets library to version 5.3.2 I've noticed the WebSocketMessageBrokerStats class no longer provides metrics for stompSubProtocolHandler. I think I've traced it down to different bean creation order between two library versions, in which the webSocketMessageBrokerStats bean is constructed before the stompWebSocketHandlerMapping which adds a stompSubProtocolHandler from adding a stomp endpoint.

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A quick summary of the difference:

Broken since Spring Boot 2.4.1 with websocket 5.3.2
Here's the call order I'm seeing in the new version:

1. Bean constructed: WebSocketMessageBrokerConfigurationSupport#subProtocolWebSocketHandler
2. Bean constructed: WebSocketMessageBrokerConfigurationSupport#webSocketMessageBrokerStats
   • subProtocolWebSocketHandler bean at this stage has no protocolHandlers and no defaultProtocolHandler
   • WebSocketMessageBrokerStats#setSubProtocolWebSocketHandler sets stompSubProtocolHandler to null
3. Bean constructed: WebSocketMessageBrokerConfigurationSupport#stompWebSocketHandlerMapping
   • calls WebSocketMessageBrokerConfigurationSupport#registerStompEndpoints
   • registry.addEndpoint(...) adds one protocolHandler to webSocketHandler
4. When trying to access WebSocketMessageBrokerStats#getStompSubProtocolStatsInfo "null" string is returned.

Was working in Spring Boot 2.4.0 with websocket 5.3.1
Call chain for the 'working' version where webSocketMessageBrokerStats.stompSubProtocolStatsInfo doesn't return null.

1. Bean constructed: WebSocketMessageBrokerConfigurationSupport#subProtocolWebSocketHandler
2. Bean constructed: WebSocketMessageBrokerConfigurationSupport#stompWebSocketHandlerMapping
   • calls WebSocketMessageBrokerConfigurationSupport#registerStompEndpoints
   • registry.addEndpoint(...) adds one protocolHandler to webSocketHandler
3. Bean constructed: WebSocketMessageBrokerConfigurationSupport#webSocketMessageBrokerStats
   • subProtocolWebSocketHandler bean at this stage has one protocolHandlers and no defaultProtocolHandler
4. When trying to access WebSocketMessageBrokerStats#getStompSubProtocolStatsInfo processed CONNECT(0)-CONNECTED(0)-DISCONNECT(0) string is returned, which is expected.

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I also created a demo app for the issue here https://github.com/countableSet/spring-websocket-metrics-bug-demo
Just flip between spring boot versions 2.4.0 and 2.4.1 you should be able to see the issue in std.out.

[rstoyanchev]

Thanks for the sample project. I am able to reproduce the issue. I'll experiment with changing WebSocketBrokerStats to an InitializingBean in order to defer its initialization.