Java Programming

I'm implementing a long poll http connection using java servlet.

How can I know that the http client is still active at any instance? Currently, what I do is to write a byte to the output stream and flush data. If there's an IO exception then the client is dead.

But in ASP.NET there is a property, Response.IsClientConnected which can find out if the client is active without writing anything to the output stream.

I want to know how if it is possible to develop in java servlet. I do not want to keep writing data into the http response stream as it may cost network.

Thanks in advance.