Tomcat example source code file (CompressionFilter.java)

This example Tomcat source code file (CompressionFilter.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Tomcat tags/keywords

accept-encoding, compressionservletresponsewrapper, compressionservletresponsewrapper, filterchain, filterconfig, filterconfig, http, httpservletrequest, httpservletresponse, io, ioexception, request, response, servlet, servletexception, servletexception, servletresponse, string, string, util

The Tomcat CompressionFilter.java source code

/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements.  See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License.  You may obtain a copy of the License at
*
*     http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

package compressionFilters;

import java.io.IOException;
import java.util.Enumeration;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


/**
 * Implementation of <code>javax.servlet.Filter used to compress
 * the ServletResponse if it is bigger than a threshold.
 *
 * @author Amy Roh
 * @author Dmitri Valdin
 * @version $Revision: 467217 $, $Date: 2006-10-24 05:14:34 +0200 (mar., 24 oct. 2006) $
 */

public class CompressionFilter implements Filter{

    /**
     * The filter configuration object we are associated with.  If this value
     * is null, this filter instance is not currently configured.
     */
    private FilterConfig config = null;

    /**
     * Minimal reasonable threshold
     */
    private int minThreshold = 128;


    /**
     * The threshold number to compress
     */
    protected int compressionThreshold;

    /**
     * Debug level for this filter
     */
    private int debug = 0;

    /**
     * Place this filter into service.
     *
     * @param filterConfig The filter configuration object
     */

    public void init(FilterConfig filterConfig) {

        config = filterConfig;
        if (filterConfig != null) {
            String value = filterConfig.getInitParameter("debug");
            if (value!=null) {
                debug = Integer.parseInt(value);
            } else {
                debug = 0;
            }
            String str = filterConfig.getInitParameter("compressionThreshold");
            if (str!=null) {
                compressionThreshold = Integer.parseInt(str);
                if (compressionThreshold != 0 && compressionThreshold < minThreshold) {
                    if (debug > 0) {
                        System.out.println("compressionThreshold should be either 0 - no compression or >= " + minThreshold);
                        System.out.println("compressionThreshold set to " + minThreshold);
                    }
                    compressionThreshold = minThreshold;
                }
            } else {
                compressionThreshold = 0;
            }

        } else {
            compressionThreshold = 0;
        }

    }

    /**
    * Take this filter out of service.
    */
    public void destroy() {

        this.config = null;

    }

    /**
     * The <code>doFilter method of the Filter is called by the container
     * each time a request/response pair is passed through the chain due
     * to a client request for a resource at the end of the chain.
     * The FilterChain passed into this method allows the Filter to pass on the
     * request and response to the next entity in the chain.<p>
     * This method first examines the request to check whether the client support
     * compression. <br>
     * It simply just pass the request and response if there is no support for
     * compression.<br>
     * If the compression support is available, it creates a
     * CompressionServletResponseWrapper object which compresses the content and
     * modifies the header if the content length is big enough.
     * It then invokes the next entity in the chain using the FilterChain object
     * (<code>chain.doFilter()), 

     **/

    public void doFilter ( ServletRequest request, ServletResponse response,
                        FilterChain chain ) throws IOException, ServletException {

        if (debug > 0) {
            System.out.println("@doFilter");
        }

        if (compressionThreshold == 0) {
            if (debug > 0) {
                System.out.println("doFilter gets called, but compressionTreshold is set to 0 - no compression");
            }
            chain.doFilter(request, response);
            return;
        }

        boolean supportCompression = false;
        if (request instanceof HttpServletRequest) {
            if (debug > 1) {
                System.out.println("requestURI = " + ((HttpServletRequest)request).getRequestURI());
            }

            // Are we allowed to compress ?
            String s = (String) ((HttpServletRequest)request).getParameter("gzip");
            if ("false".equals(s)) {
                if (debug > 0) {
                    System.out.println("got parameter gzip=false --> don't compress, just chain filter");
                }
                chain.doFilter(request, response);
                return;
            }

            Enumeration e =
                ((HttpServletRequest)request).getHeaders("Accept-Encoding");
            while (e.hasMoreElements()) {
                String name = (String)e.nextElement();
                if (name.indexOf("gzip") != -1) {
                    if (debug > 0) {
                        System.out.println("supports compression");
                    }
                    supportCompression = true;
                } else {
                    if (debug > 0) {
                        System.out.println("no support for compresion");
                    }
                }
            }
        }

        if (!supportCompression) {
            if (debug > 0) {
                System.out.println("doFilter gets called wo compression");
            }
            chain.doFilter(request, response);
            return;
        } else {
            if (response instanceof HttpServletResponse) {
                CompressionServletResponseWrapper wrappedResponse =
                    new CompressionServletResponseWrapper((HttpServletResponse)response);
                wrappedResponse.setDebugLevel(debug);
                wrappedResponse.setCompressionThreshold(compressionThreshold);
                if (debug > 0) {
                    System.out.println("doFilter gets called with compression");
                }
                try {
                    chain.doFilter(request, wrappedResponse);
                } finally {
                    wrappedResponse.finishResponse();
                }
                return;
            }
        }
    }

    /**
     * Set filter config
     * This function is equivalent to init. Required by Weblogic 6.1
     *
     * @param filterConfig The filter configuration object
     */
    public void setFilterConfig(FilterConfig filterConfig) {
        init(filterConfig);
    }

    /**
     * Return filter config
     * Required by Weblogic 6.1
     */
    public FilterConfig getFilterConfig() {
        return config;
    }

}