gzip压缩

在web.xml中的配置：

<filter>
        <filter-name>compressionFilter</filter-name>
        <filter-class>org.xblogx.base.GZIPFilter</filter-class>
</filter>
<filter-mapping>
        <filter-name>compressionFilter</filter-name>
        <url-pattern>*.jsp</url-pattern>
</filter-mapping>     

类GZIPFilter

package org.xblogx.base;

import java.io.IOException;

import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.displaytag.tags.TableTagParameters;
import org.springframework.web.filter.OncePerRequestFilter;


public class GZIPFilter extends OncePerRequestFilter ...{
    private final transient Log log = LogFactory.getLog(GZIPFilter.class);

    public void doFilterInternal(HttpServletRequest request, HttpServletResponse response, 
                                 FilterChain chain)
    throws IOException, ServletException ...{

        if (isGZIPSupported(request)) ...{
            if (log.isDebugEnabled()) ...{
                log.debug("GZIP supported, compressing response");
            }

            GZIPResponseWrapper wrappedResponse =
                new GZIPResponseWrapper(response);

            chain.doFilter(request, wrappedResponse);
            wrappedResponse.finishResponse();

            return;
        }

        chain.doFilter(request, response);
    }

    /** *//**
     * Convenience method to test for GZIP cababilities
     * @param req The current user request
     * @return boolean indicating GZIP support
     */
    private boolean isGZIPSupported(HttpServletRequest req) ...{
        
        // disable gzip filter for exporting from displaytag
        String exporting = req.getParameter(TableTagParameters.PARAMETER_EXPORTING);
        
        if (exporting != null) ...{
            log.debug("detected excel export, disabling filter...");
            return false;
        }

        String browserEncodings = req.getHeader("accept-encoding");
        boolean supported = ((browserEncodings != null) &&
                             (browserEncodings.indexOf("gzip") != -1));

        String userAgent = req.getHeader("user-agent");

        if ((userAgent != null) && userAgent.startsWith("httpunit")) ...{
            log.debug("httpunit detected, disabling filter...");

            return false;
        } else ...{
            return supported;
        }
    }
}

 类GZIPResponseStream：

package org.xblogx.base;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.util.zip.GZIPOutputStream;

import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletResponse;


/** *//**
 * Wraps Response Stream for GZipFilter
 *
 * @author  Matt Raible
 * @version $Revision: 1.3 $ $Date: 2004-05-15 20:18:10 -0600 (Sat, 15 May 2004) $
 */
public class GZIPResponseStream extends ServletOutputStream ...{
    // abstraction of the output stream used for compression
    protected OutputStream bufferedOutput = null;

    // state keeping variable for if close() has been called
    protected boolean closed = false;

    // reference to original response
    protected HttpServletResponse response = null;

    // reference to the output stream to the client's browser
    protected ServletOutputStream output = null;

    // default size of the in-memory buffer
    private int bufferSize = 50000;

    public GZIPResponseStream(HttpServletResponse response)
    throws IOException ...{
        super();
        closed = false;
        this.response = response;
        this.output = response.getOutputStream();
        bufferedOutput = new ByteArrayOutputStream();
    }

    public void close() throws IOException ...{
        // verify the stream is yet to be closed
        if (closed) ...{
            throw new IOException("This output stream has already been closed");
        }

        // if we buffered everything in memory, gzip it
        if (bufferedOutput instanceof ByteArrayOutputStream) ...{
            // get the content
            ByteArrayOutputStream baos = (ByteArrayOutputStream) bufferedOutput;

            // prepare a gzip stream
            ByteArrayOutputStream compressedContent =
                new ByteArrayOutputStream();
            GZIPOutputStream gzipstream =
                new GZIPOutputStream(compressedContent);
            byte[] bytes = baos.toByteArray();
            gzipstream.write(bytes);
            gzipstream.finish();

            // get the compressed content
            byte[] compressedBytes = compressedContent.toByteArray();

            // set appropriate HTTP headers
            response.setContentLength(compressedBytes.length);
            response.addHeader("Content-Encoding", "gzip");
            output.write(compressedBytes);
            output.flush();
            output.close();
            closed = true;
        }
        // if things were not buffered in memory, finish the GZIP stream and response
        else if (bufferedOutput instanceof GZIPOutputStream) ...{
            // cast to appropriate type
            GZIPOutputStream gzipstream = (GZIPOutputStream) bufferedOutput;

            // finish the compression
            gzipstream.finish();

            // finish the response
            output.flush();
            output.close();
            closed = true;
        }
    }

    public void flush() throws IOException ...{
        if (closed) ...{
            throw new IOException("Cannot flush a closed output stream");
        }

        bufferedOutput.flush();
    }

    public void write(int b) throws IOException ...{
        if (closed) ...{
            throw new IOException("Cannot write to a closed output stream");
        }

        // make sure we aren't over the buffer's limit
        checkBufferSize(1);

        // write the byte to the temporary output
        bufferedOutput.write((byte) b);
    }

    private void checkBufferSize(int length) throws IOException ...{
        // check if we are buffering too large of a file
        if (bufferedOutput instanceof ByteArrayOutputStream) ...{
            ByteArrayOutputStream baos = (ByteArrayOutputStream) bufferedOutput;

            if ((baos.size() + length) > bufferSize) ...{
                // files too large to keep in memory are sent to the client without Content-Length specified
                response.addHeader("Content-Encoding", "gzip");

                // get existing bytes
                byte[] bytes = baos.toByteArray();

                // make new gzip stream using the response output stream
                GZIPOutputStream gzipstream = new GZIPOutputStream(output);
                gzipstream.write(bytes);

                // we are no longer buffering, send content via gzipstream
                bufferedOutput = gzipstream;
            }
        }
    }

    public void write(byte[] b) throws IOException ...{
        write(b, 0, b.length);
    }

    public void write(byte[] b, int off, int len) throws IOException ...{

        if (closed) ...{
            throw new IOException("Cannot write to a closed output stream");
        }

        // make sure we aren't over the buffer's limit
        checkBufferSize(len);

        // write the content to the buffer
        bufferedOutput.write(b, off, len);
    }

    public boolean closed() ...{
        return (this.closed);
    }

    public void reset() ...{
        //noop
    }
}

类GZIPResponseWrapper：

package org.xblogx.base;

import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;

import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletResponseWrapper;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;


/** *//**
 * Wraps Response for GZipFilter
 *
 * @author  Matt Raible, cmurphy@intechtual.com
 */
public class GZIPResponseWrapper extends HttpServletResponseWrapper ...{
    private transient final Log log = LogFactory.getLog(GZIPResponseWrapper.class);
    protected HttpServletResponse origResponse = null;
    protected ServletOutputStream stream = null;
    protected PrintWriter writer = null;
    protected int error = 0;

    public GZIPResponseWrapper(HttpServletResponse response) ...{
        super(response);
        origResponse = response;
    }

    public ServletOutputStream createOutputStream() throws IOException ...{
        return (new GZIPResponseStream(origResponse));
    }

    public void finishResponse() ...{
        try ...{
            if (writer != null) ...{
                writer.close();
            } else ...{
                if (stream != null) ...{
                    stream.close();
                }
            }
        } catch (IOException e) ...{
        }
    }

    public void flushBuffer() throws IOException ...{
        if (stream != null) ...{
            stream.flush();
        }
    }

    public ServletOutputStream getOutputStream() throws IOException ...{
        if (writer != null) ...{
            throw new IllegalStateException("getWriter() has already been called!");
        }

        if (stream == null) ...{
            stream = createOutputStream();
        }

        return (stream);
    }

    public PrintWriter getWriter() throws IOException ...{
        // From cmurphy@intechtual.com to fix:
        // https://appfuse.dev.java.net/issues/show_bug.cgi?id=59
        if (this.origResponse != null && this.origResponse.isCommitted()) ...{
            return super.getWriter();
        }

        if (writer != null) ...{
            return (writer);
        }

        if (stream != null) ...{
            throw new IllegalStateException("getOutputStream() has already been called!");
        }

        stream = createOutputStream();
        writer =
            new PrintWriter(new OutputStreamWriter(stream,
                                                   origResponse.getCharacterEncoding()));

        return (writer);
    }

    public void setContentLength(int length) ...{
    }

    /** *//**
     * @see javax.servlet.http.HttpServletResponse#sendError(int, java.lang.String)
     */
    public void sendError(int error, String message) throws IOException ...{
        super.sendError(error, message);
        this.error = error;

        if (log.isDebugEnabled()) ...{
            log.debug("sending error: " + error + " [" + message + "]");
        }
    }
}