问题出现原因：候补

解决方案（待优化）：

public class HotSwapWatcher extends Thread {
    // 略...
    
    protected void doRun() throws IOException {
        // 略...
        while (running) {
            // 略...
           List<WatchEvent<?>> watchEvents = watchKey.pollEvents();
           for(WatchEvent<?> event : watchEvents) {
           String fileName = event.context().toString();
           if (fileName.endsWith(".class")) {
              if (undertowServer.isStarted()) {
                 restartUndertow(3);
                 resetWatchKey();
                 
                 while((watchKey = watcher.poll()) != null) {
                    // System.out.println("---> poll() ");
                    watchKey.pollEvents();
                    resetWatchKey();
                 }
                 
                 break ;
              }
           }
        }
        // 略...
    }

    private void restartUndertow(int tryTimes) {
       do {
          try {
             if (undertowServer.isStarted()) {
                undertowServer.restart();
             } else {
                undertowServer.start();
             }
          } catch (ClassFormatError e) {
             undertowServer.stop();
          } catch (RuntimeException e) {
             if (Arrays.stream(e.getSuppressed()).anyMatch(ClassNotFoundException.class::isInstance)) {
                undertowServer.stop();
             } else {
                throw e;
             }
          } finally {
             if (!undertowServer.isStarted()) {
                try {
                   Thread.sleep(66);
                } catch (InterruptedException e) {
                   e.printStackTrace();
                }
             }
          }
       } while (!undertowServer.isStarted() && --tryTimes > 0);
    }
    
    // 略...
}