title: Why can I see o, io, nio threads in my Spring Boot logs?
body: <p>I run a test case in my springboot project (base version 2.1.0.R and tomcat 9 in web-starter) ：</p>
  <pre><code>@RequestMapping(&quot;test&quot;)
  public String test() throws InterruptedException {
      Thread.sleep(10000);
      logger.info(Thread.activeCount()+&quot;&quot;);
      return &quot;&quot;;
  }
  </code></pre>
  <p>and then I send many concurrent request(more than 300 requests at almost same time).in this log：</p>
  <p>2020-03-21 10:53:19.866  INFO 33092 --- [nio-8080-exec-4]                                          : 209</p>
  <p>2020-03-21 10:53:19.868  INFO 33092 --- [o-8080-exec-111]                                          : 209</p>
  <p>2020-03-21 10:53:19.869  INFO 33092 --- [io-8080-exec-62]                                          : 209</p>
  <p>2020-03-21 10:53:19.870  INFO 33092 --- [io-8080-exec-70]                                          : 209</p>
  <p>In my options ,I can only see nio threads in it due to Tomcat 9, so I can't unterstand this log. I want to know why.</p>
  <p>Sorry for my poor English leavel.
  <a href="https://i.stack.imgur.com/VyqjY.png" rel="nofollow noreferrer">log image</a></p>