Convert comment to the answer. @adam-arold said it works

@EventListener 
public void onContextClosed(ContextClosedEvent event) {
    closeAllEmitters(); 
}

private void closeAllEmitters() {     
    List<SseEmitter> allEmitters = emitters.values().stream()             
        .flatMap(List::stream)             
        .collect(Collectors.toList());     
    for (SseEmitter emitter : allEmitters) {         
        try {             
            emitter.complete();         
        } catch (Exception e) {             
            log.error("Error during emitter completing");         
        }     
    }
    emitters.clear(); 
}