GZIP Http Servlet Response

Liang Ding
* @version 1.0.0.1, Dec 16, 2010
*/
public abstract class AbstractGZIPFilter implements Filter {

/**
* Logger.
*/
private static final Logger LOGGER =
Logger.getLogger(AbstractGZIPFilter.class.getName());

@Override
public void init(final FilterConfig cfg) throws ServletException {
}

/**
* Wraps the http servlet response with GZIP if could.
*
* @param request the specified request
* @param response the specified response
* @param chain filter chain
* @throws IOException io exception
* @throws ServletException servlet exception
*/
@Override
public void doFilter(final ServletRequest request,
final ServletResponse response,
final FilterChain chain) throws IOException,
ServletException {
final HttpServletRequest httpServletRequest =
(HttpServletRequest) request;
final String requestURI = httpServletRequest.getRequestURI();
if (shouldSkip(requestURI)) {
LOGGER.log(Level.FINEST, "Skip GZIP filter request[URI={0}]",
requestURI);
chain.doFilter(request, response);

return;
}

final String acceptEncoding =
httpServletRequest.getHeader("Accept-Encoding");
boolean supportGZIP = false;
if (null != acceptEncoding
&& 0 <= acceptEncoding.indexOf("gzip")) {
supportGZIP = true;
}

if (!supportGZIP) {
LOGGER.info("Gzip NOT be supported");
chain.doFilter(request, response);

return;
}

final HttpServletResponse httpServletResponse =
(HttpServletResponse) response;
httpServletResponse.addHeader("Content-Encoding", "gzip");
httpServletResponse.addHeader("Vary", "Accept-Encoding");
chain.doFilter(request,
new GZIPServletResponseWrapper(httpServletResponse));
}

/**
* Determines whether the specified request URI should be skipped filter.
*
*
*   Note: This method SHOULD be invoked for all filters with pattern
*   "/*".
*

*
* @param requestURI the specified request URI
* @return {@code true} if should be skipped, {@code false} otherwise
*/
public abstract boolean shouldSkip(final String requestURI);

@Override
public void destroy() {
}

/**
* HTTP response wrapper for GZIP.
*
* @author Liang Ding
* @version 1.0.0.0, Dec 16, 2010
*/
private class GZIPServletResponseWrapper extends HttpServletResponseWrapper {

/**
* GZIP output stream.
*/
private GZIPOutputStream gzipStream;
/**
* Servlet output stream.
*/
private ServletOutputStream servletOutputStream;
/**
* Print writer.
*/
private PrintWriter printWriter;

/**
* Constructs an {@link GZIPServletResponseWrapper} object with the
* specified http servlet response.
*
* @param httpServletResponse the specified http servlet response
* @throws IOException io exception
*/
GZIPServletResponseWrapper(final HttpServletResponse httpServletResponse)
throws IOException {
super(httpServletResponse);
}

@Override
public ServletOutputStream getOutputStream() throws IOException {
if (null == servletOutputStream) {
servletOutputStream = createOutputStream();
}

return servletOutputStream;
}

@Override
public PrintWriter getWriter() throws IOException {
if (null == printWriter) {
printWriter = new PrintWriter(
new OutputStreamWriter(getOutputStream(),
getCharacterEncoding()));
}

return printWriter;
}

/**
* Creates output stream with GZIP delegation.
*
* @return servlet output stream
* @throws IOException io exception
*/
private ServletOutputStream createOutputStream() throws IOException {
final ServletResponse servletResponse = this.getResponse();
gzipStream = new GZIPOutputStream(servletResponse.getOutputStream());

return new ServletOutputStream() {

@Override
public void write(final int b) throws IOException {
gzipStream.write(b);
}

@Override
public void flush() throws IOException {
gzipStream.flush();
}

@Override
public void close() throws IOException {
gzipStream.close();
}

/*
* These two are not absolutely needed. They are here simply
* because they were overriden by GZIPOutputStream.
*/
@Override
public void write(final byte[] b) throws IOException {
gzipStream.write(b);
}

@Override
public void write(final byte[] b, final int off, final int len)
throws IOException {
gzipStream.write(b, off, len);
}
};
}
}
}