How do I view a message from a filter?

I tried to use a javax.servlet.Filter to peek into a message.

public void doFilter( ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
     BufferedReader reader = request.getReader();
     if ( reader.markSupported() ) {
         reader.mark( contentLen );
     }
     String content = reader.readLine();

     // search some pattern

     if ( reader.markSupported() ) {
         reader.reset();
     }
     chain.doFilter( request, response );
}

The servlet that finally receives the request throws this exeption:

java.lang.IllegalStateException: getReader() has already been called for this request

Which is correct behaviour according to the javadoc.

My questions is how can I read the content of the input-stream anyway?

I also tried ServletInputStream is = request.getInputStream();

Not tested, but you could probably

• read all the bytes from the request input stream and write them to a byte array,
• construct a buffered reader over this byte array to read what you want in the filter,
• construct a HttpServletRequestWrapper which overrides getInputStream() to return a stream over the byte array,
• pass this wrapper to the filter chain.