gzipencodefilter.java

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package tw.com.javaworld.CH11;

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.util.zip.GZIPOutputStream;

public class GZIPEncodeFilter implements Filter {
	
	public void init(FilterConfig filterConfig) {
	}
	
	public void doFilter(
		ServletRequest request,
		ServletResponse response,
		FilterChain chain)
		throws IOException, ServletException {
		String transferEncoding = getGZIPEncoding((HttpServletRequest) request);
		if (transferEncoding == null) {
			chain.doFilter(request, response);
		} else {
			((HttpServletResponse) response).setHeader(
				"Content-Encoding",
				transferEncoding);
			GZIPEncodableResponse wrappedResponse =
				new GZIPEncodableResponse((HttpServletResponse) response);
			chain.doFilter(request, wrappedResponse);
			wrappedResponse.flush();
		}
	}
	
	public void destroy() {
	}
	
	private static String getGZIPEncoding(HttpServletRequest request) {
		String acceptEncoding = request.getHeader("Accept-Encoding");
		if (acceptEncoding == null)
			return null;
		acceptEncoding = acceptEncoding.toLowerCase();
		if (acceptEncoding.indexOf("x-gzip") >= 0) {
			return "x-gzip";
		}
		if (acceptEncoding.indexOf("gzip") >= 0) {
			return "gzip";
		}
		return null;
	}
	
	private class GZIPEncodableResponse extends HttpServletResponseWrapper {
		private GZIPServletStream wrappedOut;
		public GZIPEncodableResponse(HttpServletResponse response)
			throws IOException {
			super(response);
			wrappedOut = new GZIPServletStream(response.getOutputStream());
		}
		public ServletOutputStream getOutputStream() throws IOException {
			return wrappedOut;
		}
		private PrintWriter wrappedWriter;
		public PrintWriter getWriter() throws IOException {
			if (wrappedWriter == null) {
				wrappedWriter =
					new PrintWriter(
						new OutputStreamWriter(
							getOutputStream(),
							getCharacterEncoding()));
			}
			return wrappedWriter;
		}
		public void flush() throws IOException {
			if (wrappedWriter != null) {
				wrappedWriter.flush();
			}
			wrappedOut.finish();
		}
	}
	
	private class GZIPServletStream extends ServletOutputStream {
		private GZIPOutputStream outputStream;
		public GZIPServletStream(OutputStream source) throws IOException {
			outputStream = new GZIPOutputStream(source);
		}
		public void finish() throws IOException {
			outputStream.finish();
		}
		public void write(byte[] buf) throws IOException {
			outputStream.write(buf);
		}
		public void write(byte[] buf, int off, int len) throws IOException {
			outputStream.write(buf, off, len);
		}
		public void write(int c) throws IOException {
			outputStream.write(c);
		}
		public void flush() throws IOException {
			outputStream.flush();
		}
		public void close() throws IOException {
			outputStream.close();
		}
	}
}