使用ResposeWrapper的响应筛选器

Question

I came across a portion of code that zips the servlet output before returning it to the user, it uses a custom ServletResponseWrapper -it's so famous if u know what I am talking about-, my questions are :

1 - now the function of intercepting the response is totally the responsibility of the response wrapper -through overriding the output stream it returns- and the filter has no effect in such behaviour ? Am I correct ?

2- what happens if any of the servlets that the filters intercept its requests closed the output stream, will the code after chain.doFilter() be able to use this stream again ? and will the filter work ?

3 why does the wrapped response solve the problem of the "output returns directly to the container before being intercepted by the filter" ... I mean why the control over the response is then returned to the filter ?

Answer 1

I've recently used the example code from this book for my project: Professional Java for Web Applications . There is a good example for a compression filter in chapter 9.

I'm not involved with the company behind the book.

These are the answers to your question:

1. Yes, you're correct. The filter wraps the original HttpServletResponse with a wrapper, and from this moment on the wrapper is responsible for managing the output stream (but not for closing the stream).
2. It's not a good idea at all to close the output stream in your own code, whether you use a wrapped HttpServletResponse or not.
3. The control over the output stream isn't returned to the filter. The execution of your web app is continued in the line after chain.doFilter() , and you can write some data to the wrapped response, if it's necessary. But don't close the stream, neither in your filter, nor in your servlet(s).