title: How solve Error: java.lang.ClassNotFoundException: io.netty.util.concurrent.GenericFutureListener?
body: <p>yeserday in first time I did try to make Prometheus Client by Java (did begin from Python, last did is GoLang).</p>
  
  <p>Did find Example</p>
  
  <pre><code>import io.prometheus.client.Counter;
  import io.prometheus.client.Gauge;
  import io.prometheus.client.Histogram;
  import io.prometheus.client.Summary;
  import io.prometheus.client.vertx.MetricsHandler;
  import io.vertx.core.Vertx;
  import io.vertx.ext.web.Router;
  //import io.prometheus.client.vertx.MetricsHandler;
  
  public class ExampleExporter {
  
      static final Gauge g = Gauge.build().name("gauge").help("blah").register();
      static final Counter c = Counter.build().name("counter").help("meh").register();
      static final Summary s = Summary.build().name("summary").help("meh").register();
      static final Histogram h = Histogram.build().name("histogram").help("meh").register();
      static final Gauge l = Gauge.build().name("labels").help("blah").labelNames("l").register();
  
      public static  void main(String[] args) throws Exception {
          final Vertx vertx = Vertx.vertx();
          final Router router = Router.router(vertx);
  
          router.route("/metrics").handler(new MetricsHandler());
  
          vertx.createHttpServer().requestHandler(router::accept).listen(8001);
  
          g.set(1);
          c.inc(2);
          s.observe(3);
          h.observe(4);
          l.labels("foo").inc(5);
      }
  
  
  
  }
  </code></pre>
  
  <p>Did load from Maven Libraries.</p>
  
  <p>After did try run client, did return error:</p>
  
  <pre><code>Exception in thread "main" java.lang.NoClassDefFoundError: io/netty/util/concurrent/GenericFutureListener
      at io.vertx.core.impl.VertxFactoryImpl.vertx(VertxFactoryImpl.java:30)
      at io.vertx.core.Vertx.vertx(Vertx.java:78)
      at ExampleExporter.main(ExampleExporter.java:22)
  Caused by: java.lang.ClassNotFoundException: io.netty.util.concurrent.GenericFutureListener
      at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
      at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
      at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:349)
      at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
      ... 3 more
  </code></pre>
  
  <p>All code and lib did upload
  <a href="https://github.com/drno-reg/ExamplePrometheusNode.git" rel="nofollow noreferrer">Git Repository</a></p>
  
  <p>Please help to solve this problem.</p>