启动jetty服务器：

$ mvn jetty:run

测试请求：

$ http localhost:8080/app/forward
HTTP/1.1 200 OK
Content-Length: 14
Content-Type: text/plain;charset=utf-8
Date: Fri, 20 Dec 2019 10:21:27 GMT
Server: Jetty(9.4.17.v20190418)

forwarded: foo

可以看到internalDispatcher把请求转发给了foo。