nanolets/src/main/java/org/nanohttpd/router/RouterNanoHTTPD.java
public void addMappings() {
        router.setNotImplemented(NotImplementedHandler.class);
        router.setNotFoundHandler(Error404UriHandler.class);
        router.addRoute("/", Integer.MAX_VALUE / 2, IndexHandler.class);
        router.addRoute("/index.html", Integer.MAX_VALUE / 2, IndexHandler.class);
    }
public void addMappings() {
        router.setNotImplemented(NotImplementedHandler.class);
        router.setNotFoundHandler(Error404UriHandler.class);
        router.addRoute("/", Integer.MAX_VALUE / 2, IndexHandler.class);
        router.addRoute("/index.html", Integer.MAX_VALUE / 2, IndexHandler.class);
    }
default routings, they are over writable.

<pre>
router.setNotFoundHandler(GeneralHandler.class);
</pre>