request.startAsync()不支持异步操作

Servlet3.0使用异步处理时，后台报错：

java.lang.IllegalStateException: A filter or servlet of the current chain does not support asynchronous operations.

必须在一个请求所涉及到的Servlet和Filter中声明asyncSupported=true

如果web.xml配置了Servlet和Filter也要添加<async-supported>true</async-supported>。比如web.xml配置了UrlRewriteFilter等