无法从config exception = java.lang.NullPointerException实例化Dispatcher

Question

我正在使用Pushlet将消息从服​​务器端推送到网页并获得上述错误。有人知道为什么会这样吗？

public void run() {
    DataInputStream input;
    try {
        input = new DataInputStream(socket.getInputStream());
        String json = input.readUTF();
        input.close();

        System.out.println("msg from client: " + json);
        String subject = "/pushlet/ping";
        Event event = Event.createDataEvent(subject);
        event.setField("msg", json);
        Dispatcher.getInstance().multicast(event);
      } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
      }
}

这是web.xml。

<!-- Define the pushlet servlet -->
<servlet>
<servlet-name>pushlet</servlet-name>
<servlet-class>nl.justobjects.pushlet.servlet.Pushlet</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>

<!-- Define the Servlet Mappings. -->

<!-- The pushlet -->
<servlet-mapping>
<servlet-name>pushlet</servlet-name>
<url-pattern>/pushlet.srv</url-pattern>
</servlet-mapping>