title: Why there is no exception stack trace in spring webflux with default configuration?
body: <h2>Question</h2>
  <p>I built a server following <a href="https://www.baeldung.com/spring-5-functional-web" rel="nofollow noreferrer">Webflux functional programming</a>, and added below code to my Router: <code>route(GET(&quot;/test/{Id}&quot;), request -&gt; throw new RuntimeException(&quot;123&quot;))</code>.</p>
  <p>But when I call <code>/test/{Id}</code>, the only error log in console is:</p>
  <pre><code>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
  </code></pre>
  <p><strong>No stack trace, but why?</strong> It should be handled by spring or netty, not my customized code, right? Setting <code>logging.level.org.springframework.web: trace</code> is not a solution, there're too many logs.</p>
  <h2>Here is what I found so far, but still confused:</h2>
  <p>I've checked why spring mvc has stack trace, because there is a <a href="https://github.com/apache/tomcat/blob/trunk/java/org/apache/catalina/core/StandardWrapperValve.java#L236" rel="nofollow noreferrer">log.error in try-catch</a> in tomcat and it's proven by debugging.</p>
  <p>Then I thought does Netty has these logic too? Actually it <a href="https://github.com/reactor/reactor-netty/blob/master/src/main/java/reactor/netty/http/server/HttpServerHandle.java#L67" rel="nofollow noreferrer">has</a>! But what's confuse me is that I can't pause the code in this try-catch with any breakpoints.</p>
  <p>Which means there may exists some <code>Mono.onErrorResume</code> 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?</p>