title: How to add a request logging filter in Jetty 8?
body: <p>Here is how I setup my Jetty server:</p>
  
  <pre><code>Server server = new Server(80);
  server.setStopAtShutdown(true);
  
  ServletHandler servletHandler = new ServletHandler();
  servletHandler.addServletWithMapping(Erreur500Servlet.class, "/generate-error-500");
  servletHandler.addServletWithMapping(AresServlet.class, "/ares/*");
  servletHandler.addFilterWithMapping(RequestLoggingFilter.class, "/*", EnumSet.of(DispatcherType.REQUEST));
  
  server.setHandler(servletHandler);
  server.start(); // at com.company.MyPoc.init(MyPoc.java:44)
  server.join();
  </code></pre>
  
  <p>However, when it starts, I got the following exception:</p>
  
  <pre><code>2015-10-20 12:53:07,565 (?:?) [WARN] FAILED com.company.filter.RequestLoggingFilter-896472140: java.lang.NullPointerException 
  java.lang.NullPointerException: null
      at org.eclipse.jetty.servlet.FilterHolder.doStart(FilterHolder.java:100) ~[jetty-servlet-8.0.1.v20110908.jar:8.0.1.v20110908]
      at org.eclipse.jetty.util.component.AbstractLifeCycle.start(AbstractLifeCycle.java:59) [jetty-util-8.0.1.v20110908.jar:8.0.1.v20110908]
      at org.eclipse.jetty.servlet.ServletHandler.initialize(ServletHandler.java:753) [jetty-servlet-8.0.1.v20110908.jar:8.0.1.v20110908]
      at org.eclipse.jetty.servlet.ServletHandler.doStart(ServletHandler.java:183) [jetty-servlet-8.0.1.v20110908.jar:8.0.1.v20110908]
      at org.eclipse.jetty.util.component.AbstractLifeCycle.start(AbstractLifeCycle.java:59) [jetty-util-8.0.1.v20110908.jar:8.0.1.v20110908]
      at org.eclipse.jetty.server.handler.HandlerWrapper.doStart(HandlerWrapper.java:89) [jetty-server-8.0.1.v20110908.jar:8.0.1.v20110908]
      at org.eclipse.jetty.server.Server.doStart(Server.java:262) [jetty-server-8.0.1.v20110908.jar:8.0.1.v20110908]
      at org.eclipse.jetty.util.component.AbstractLifeCycle.start(AbstractLifeCycle.java:59) [jetty-util-8.0.1.v20110908.jar:8.0.1.v20110908]
      at com.company.MyPoc.init(MyPoc.java:44) 
  </code></pre>
  
  <p>What am I missing?</p>
  
  <p><strong>Jetty 8.0.1.v20110908</strong></p>