Http Servlet request lose params from POST body after read it once

Question

I\'m trying to accessing two http request parameters in a Java Servlet filter, nothing new here, but was surprised to find that the parameters have already been consumed! Be

Answer 1

The only way would be for you to consume the entire input stream yourself in the filter, take what you want from it, and then create a new InputStream for the content you read, and put that InputStream in to a ServletRequestWrapper (or HttpServletRequestWrapper).

The downside is you'll have to parse the payload yourself, the standard doesn't make that capability available to you.

Addenda --

As I said, you need to look at HttpServletRequestWrapper.

In a filter, you continue along by calling FilterChain.doFilter(request, response).

For trivial filters, the request and response are the same as the ones passed in to the filter. That doesn't have to be the case. You can replace those with your own requests and/or responses.

HttpServletRequestWrapper is specifically designed to facilitate this. You pass it the original request, and then you can intercept all of the calls. You create your own subclass of this, and replace the getInputStream method with one of your own. You can't change the input stream of the original request, so instead you have this wrapper and return your own input stream.

The simplest case is to consume the original requests input stream in to a byte buffer, do whatever magic you want on it, then create a new ByteArrayInputStream from that buffer. This is what is returned in your wrapper, which is passed to the FilterChain.doFilter method.

You'll need to subclass ServletInputStream and make another wrapper for your ByteArrayInputStream, but that's not a big deal either.