Java tutorial
/** * Copyright 2003-2007 Luck Consulting Pty Ltd * * Licensed 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 net.sf.ehcache.constructs.web; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; /** * A collection of response processing utilities, which are shared between 2 or more filters * * @author Greg Luck * @version $Id: ResponseUtil.java 519 2007-07-27 07:11:45Z gregluck $ */ public final class ResponseUtil { private static final Log LOG = LogFactory.getLog(ResponseUtil.class.getName()); /** * Gzipping an empty file or stream always results in a 20 byte output * This is in java or elsewhere. * <p/> * On a unix system to reproduce do <code>gzip -n empty_file</code>. -n tells gzip to not * include the file name. The resulting file size is 20 bytes. * <p/> * Therefore 20 bytes can be used indicate that the gzip byte[] will be empty when ungzipped. */ private static final int EMPTY_GZIPPED_CONTENT_SIZE = 20; /** * Utility class. No public constructor. */ private ResponseUtil() { //noop } /** * Checks whether a gzipped body is actually empty and should just be zero. * When the compressedBytes is {@link #EMPTY_GZIPPED_CONTENT_SIZE} it should be zero. * * @param compressedBytes the gzipped response body * @param request the client HTTP request * @return true if the response should be 0, even if it is isn't. */ public static boolean shouldGzippedBodyBeZero(byte[] compressedBytes, HttpServletRequest request) { //Check for 0 length body if (compressedBytes.length == EMPTY_GZIPPED_CONTENT_SIZE) { if (LOG.isDebugEnabled()) { LOG.debug(request.getRequestURL() + " resulted in an empty response."); } return true; } else { return false; } } /** * Performs a number of checks to ensure response saneness according to the rules of RFC2616: * <ol> * <li>If the response code is {@link javax.servlet.http.HttpServletResponse#SC_NO_CONTENT} then it is illegal for the body * to contain anything. See http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.2.5 * <li>If the response code is {@link javax.servlet.http.HttpServletResponse#SC_NOT_MODIFIED} then it is illegal for the body * to contain anything. See http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.3.5 * </ol> * * @param request the client HTTP request * @param responseStatus the responseStatus * @return true if the response should be 0, even if it is isn't. */ public static boolean shouldBodyBeZero(HttpServletRequest request, int responseStatus) { //Check for NO_CONTENT if (responseStatus == HttpServletResponse.SC_NO_CONTENT) { if (LOG.isDebugEnabled()) { LOG.debug(request.getRequestURL() + " resulted in a " + HttpServletResponse.SC_NO_CONTENT + " response. Removing message body in accordance with RFC2616."); } return true; } //Check for NOT_MODIFIED if (responseStatus == HttpServletResponse.SC_NOT_MODIFIED) { if (LOG.isDebugEnabled()) { LOG.debug(request.getRequestURL() + " resulted in a " + HttpServletResponse.SC_NOT_MODIFIED + " response. Removing message body in accordance with RFC2616."); } return true; } return false; } /** * Adds the gzip HTTP header to the response. This is need when a gzipped body is returned so that browsers can properly decompress it. * <p/> * @param response the response which will have a header added to it. I.e this method changes its parameter * @throws ResponseHeadersNotModifiableException Either the response is committed or we were called using the include method * from a {@link javax.servlet.RequestDispatcher#include(javax.servlet.ServletRequest, javax.servlet.ServletResponse)} * method and the set set header is ignored. */ public static void addGzipHeader(final HttpServletResponse response) throws ResponseHeadersNotModifiableException { response.setHeader("Content-Encoding", "gzip"); boolean containsEncoding = response.containsHeader("Content-Encoding"); if (!containsEncoding) { throw new ResponseHeadersNotModifiableException( "Failure when attempting to set " + "Content-Encoding: gzip"); } } }