I'm using the following construction (simplified):
@Component
class RuleProvider {
public Stream<String> getRules() {
return Stream.of("r1", "r2", "r3");
}
}
@Service
class RuleService {
@Autowired RuleProvider ruleProvider;
public void evaluateRules() {
ruleProvider.getRules().foreach(System.out::println);
}
}
and I use Spring AOP to perform logging. Now I'd like to log all the rules that are handed to the service. In general, this should do it:
@Aspect
class LoggingAspect {
@AfterReturning(value="execution(* *..RuleProvider.getRules(*))",
returning="rules")
void logRules(JoinPoint jp, Stream<String> rules) {
Logger logger = LoggerFactory.getLogger(jp.getTarget().getClass());
rules.peek(rule -> logger.debug("evaluating {}", rule);
}
}
This should work - the aspect is evaluated, registers the peek intermediate operation, and once the foreach() terminal op is performed, the logging should also to done.
However, when I run this, the Stream seems to get closed after the aspect has run - I get a "stream has already been operated upon or closed" in the service method.
Why is the Stream being closed? Is there anything I can do against that?
The stream is not closed, but it obviously "has already been operated on" exactly as the error message says. Consider how peek is normally used:
Stream.of(...)
.peek(...)
.other_operations(...);
Note that the other_operations() are acting on the Stream returned by peek(), and not on the original stream. What you are doing with the aspect is analogous to this:
Stream s = Stream.of(...);
s.peek(...);
s.other_operations(...);
What you can do to fix this is to replace the return value, e.g. by using an @Around aspect.