CompressionFilter.javaAPI DocExample2654Thu Oct 21 10:31:48 BST 2004com.example


public class CompressionFilter extends Object implements Filter
This filter provides a mechanism to compress the response body content. This type of filter would common be applied to any text content, such as HTML, but not to most media formats, such as PNG or MPEG, because these are already compressed.

Fields Summary
private ServletContext
private FilterConfig
Constructors Summary
Methods Summary
public voiddestroy()

      // nulling out my instance variables
      cfg = null;
      ctx = null;
public voiddoFilter(javax.servlet.ServletRequest req, javax.servlet.ServletResponse resp, javax.servlet.FilterChain fc)
The heart of this filter wraps the response object with a Decorator that wraps the output stream with a compression I/O stream. Compression of the output stream is only performed if and only if the client includes an Accept-Encoding header (specifically, for gzip).

    HttpServletRequest request = (HttpServletRequest) req;
    HttpServletResponse response = (HttpServletResponse) resp;

    // Dose the client accept GZIP compression?
    String valid_encodings = request.getHeader("Accept-Encoding");
    if ( (valid_encodings != null) && (valid_encodings.indexOf("gzip") > -1) ) {

      // Then wrap the response object with a compression wrapper
      // We'll look at this class in a minute.
      CompressionResponseWrapper wrappedResp
	= new CompressionResponseWrapper(response);

      // Declare that the response content is being GZIP encoded.
      wrappedResp.setHeader("Content-Encoding", "gzip");

      // Chain to the next component (thus processing the request)
      fc.doFilter(request, wrappedResp);

      // A GZIP compression stream must be "finished" which also
      // flushes the GZIP stream buffer which sends all of its
      // data to the original response stream.
      GZIPOutputStream gzos = wrappedResp.getGZIPOutputStream();
      // The container handles the rest of the work.

      ctx.log(cfg.getFilterName() + ": finished the request.");

    } else {
      fc.doFilter(request, response);
      ctx.log(cfg.getFilterName() + ": no encoding performed.");
public voidinit(javax.servlet.FilterConfig cfg)
The init method saves the config object and a quick reference to the servlet context object (for logging purposes).

    this.cfg = cfg;
    ctx = cfg.getServletContext();
    ctx.log(cfg.getFilterName() + " initialized.");