Why there is no exception stack trace in spring webflux with default configuration?

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Question

I built a server following Webflux functional programming, and added below code to my Router: route(GET("/test/{Id}"), request -> throw new RuntimeException("123")).

But when I call /test/{Id}, the only error log in console is:

TRACE 153036 --- [ctor-http-nio-7] o.s.w.r.function.server.RouterFunctions  : [fc7e809d] Matched org.springframework.web.reactive.function.server.RequestPredicates$$Lambda$827/1369035321@9d8c274
DEBUG 153036 --- [ctor-http-nio-7] org.springframework.web.HttpLogging      : [fc7e809d] Resolved [RuntimeException: 123] for HTTP GET /test/job
TRACE 153036 --- [ctor-http-nio-7] org.springframework.web.HttpLogging      : [fc7e809d] Encoding [{timestamp=Mon Dec 17 15:34:43 CST 2018, path=/test/123, status=500, error=Internal Server Error, message=123}]
TRACE 153036 --- [ctor-http-nio-7] o.s.w.s.adapter.HttpWebHandlerAdapter    : [fc7e809d] Completed 500 INTERNAL_SERVER_ERROR, headers={masked}
TRACE 153036 --- [ctor-http-nio-7] org.springframework.web.HttpLogging      : [fc7e809d] Handling completed

No stack trace, but why? It should be handled by spring or netty, not my customized code, right? Setting logging.level.org.springframework.web: trace is not a solution, there're too many logs.

Here is what I found so far, but still confused:

I've checked why spring mvc has stack trace, because there is a log.error in try-catch in tomcat and it's proven by debugging.

Then I thought does Netty has these logic too? Actually it has! But what's confuse me is that I can't pause the code in this try-catch with any breakpoints.

Which means there may exists some Mono.onErrorResume swallowing the exception, so netty can't catch anything. But I don't know how to debug a large Mono to check the root cause. And why swallow it?

project-reactor spring-webflux spring-boot netty spring
1 Answers

Option 1A: Set application properties as follows:

server.error.includeStacktrace=ALWAYS

Option 1B: Set application properties as follows:

server.error.includeStacktrace=ON_TRACE_PARAM

And, specify request parameter trace to true.

Option 2: Add a customized WebExceptionHandler, and make sure it's in the component scan scope.

@Component
@Order(-2)
public class LoggingErrorWebExceptionHandler extends DefaultErrorWebExceptionHandler {
    private static final Logger logger = LoggerFactory.getLogger(LoggingErrorWebExceptionHandler.class);

    public LoggingErrorWebExceptionHandler(ErrorAttributes errorAttributes, ResourceProperties resourceProperties,
            ServerProperties serverProperties, ApplicationContext applicationContext, ServerCodecConfigurer serverCodecConfigurer) {
        super(errorAttributes, resourceProperties, serverProperties.getError(), applicationContext);
        super.setMessageWriters(serverCodecConfigurer.getWriters());
        super.setMessageReaders(serverCodecConfigurer.getReaders());
    }

    @Override
    protected void logError(ServerRequest request, HttpStatus errorStatus) {
        Throwable ex = getError(request);
        logger.error("Error Occurred:", ex);
        super.logError(request, errorStatus);
    }

}

See https://www.baeldung.com/spring-webflux-errors for more details.

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