Allow customizing of DefaultSubscriptionRegistry messageEvalContext [SPR-17485]

David Melia opened SPR-17485 and commented

Hi,

org.springframework.messaging.simp.broker.DefaultSubscriptionRegistry contains

private static EvaluationContext messageEvalContext =
          SimpleEvaluationContext.forPropertyAccessors(new SimpMessageHeaderPropertyAccessor()).build();

but with no way to override it.

If you think about a stock broking site contain 1000s of price updates I need the ability to add a selector header to filter only the stocks that the customer is interested in. To do that using the default cut down EvaluationContext the selector would be very clunky.

If I can add my own function to the evaluation context i.e

messageEvalContext.setVariable("myCustomStockSymbolFilterFunction" . . .

then the selector would be simplified i.e.

#myCustomStockSymbolFilterFunction(headers['simpDestination'],{'MSFT','BARC'})

Therefore:

• Could you add the ability to override the EvaluationContext? 

• If so would it be possible to make SimpMessageHeaderPropertyAccessor available somehow?

Thanks

Affects: 5.1.2

Start with org.springframework.messaging.simp.broker.DefaultSubscriptionRegistry and inspect how its messageEvalContext is used for selector evaluation. Review SimpMessageHeaderPropertyAccessor and determine the supported customization boundary. Done means the EvaluationContext can be overridden and the accessor can be used for custom selector functions.