在异步的servlet获得最重要的事情是 HTTP推时，其中，服务器可以触发信息返回给客户端时，它选择，而不是在客户端要求它。 $ P $对非同步的servlet，这将需要长时间运行的HTTP连接，其中每个捆绑一个服务器线程，这是非常低效的。这种新的模型从连接处理解耦服务器端处理

The big thing you get with asynchronous servlets is HTTP push, where the server can fire information back to the client when it chooses to, rather than when the client asks for it. Pre-asynch servlets, this would require long-running HTTP connections which each tied up a server thread, which is very inefficient. This new model decouples the server-side processing from the connection handling.