1  /*
     2   * Licensed to the Apache Software Foundation (ASF) under one or more
     3   *  contributor license agreements.  The ASF licenses this file to You
     4   * under the Apache License, Version 2.0 (the "License"); you may not
     5   * use this file except in compliance with the License.
     6   * You may obtain a copy of the License at
     7   *
     8   *     http://www.apache.org/licenses/LICENSE-2.0
     9   *
    10   * Unless required by applicable law or agreed to in writing, software
    11   * distributed under the License is distributed on an "AS IS" BASIS,
    12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13   * See the License for the specific language governing permissions and
    14   * limitations under the License.  For additional information regarding
    15   * copyright in this work, please see the NOTICE file in the top level
    16   * directory of this distribution.
    17   */
    18  
    19  package org.apache.roller.weblogger.ui.rendering.util;
    20  
    21  import org.apache.commons.logging.Log;
    22  import org.apache.commons.logging.LogFactory;
    23  
    24  import javax.servlet.http.HttpServletRequest;
    25  import javax.servlet.http.HttpServletResponse;
    26  
    27  /**
    28   * Utility class to localize the modification date header-related logic.
    29   */
    30  public class ModDateHeaderUtil {
             /* 
    P/P       *  Method: org.apache.roller.weblogger.ui.rendering.util.ModDateHeaderUtil__static_init
              * 
              *  Postconditions:
              *    init'ed(log)
              */
    31      private static final Log log = LogFactory.getLog(ModDateHeaderUtil.class);
    32  
    33      // Utility class with static methods; inhibit construction
             /* 
    P/P       *  Method: void org.apache.roller.weblogger.ui.rendering.util.ModDateHeaderUtil()
              */
    34      private ModDateHeaderUtil() {
    35  
    36      }
    37  
    38      /**
    39       * Sets the HTTP response status to 304 (NOT MODIFIED) if the request contains an
    40       * If-Modified-Since header that specifies a time that is
    41       * at or after the time specified by the value of lastModifiedTimeMillis
    42       * <em>truncated to second granularity</em>.  Returns true if
    43       * the response status was set, false if not.
    44       *
    45       * @param request
    46       * @param response
    47       * @param lastModifiedTimeMillis
    48       * @return true if a response status was sent, false otherwise.
    49       */
    50      public static boolean respondIfNotModified(HttpServletRequest request,
    51                                                 HttpServletResponse response,
    52                                                 long lastModifiedTimeMillis) {
                 /* 
    P/P           *  Method: bool respondIfNotModified(HttpServletRequest, HttpServletResponse, long)
                  * 
                  *  Preconditions:
                  *    (soft) lastModifiedTimeMillis%1_000 - lastModifiedTimeMillis in -264+1..263
                  *    (soft) request != null
                  *    (soft) response != null
                  * 
                  *  Presumptions:
                  *    org.apache.commons.logging.LogFactory:getLog(...)@31 != null
                  * 
                  *  Postconditions:
                  *    init'ed(return_value)
                  */
    53          long sinceDate = 0;
    54          try {
    55              sinceDate = request.getDateHeader("If-Modified-Since");
    56          } catch(IllegalArgumentException ex) {
    57              // this indicates there was some problem parsing the header value as a date
    58              return false;
    59          }
    60          
    61          // truncate to seconds
    62          lastModifiedTimeMillis -= (lastModifiedTimeMillis % 1000);
    63          log.debug("since date = " + sinceDate);
    64          log.debug("last mod date (trucated to seconds) = " + lastModifiedTimeMillis);
    65          if (lastModifiedTimeMillis <= sinceDate) {
    66              log.debug("NOT MODIFIED " + request.getRequestURL());
    67              response.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
    68              return true;
    69          } else {
    70              return false;
    71          }
    72      }
    73  
    74      /**
    75       * Set the Last-Modified header using the given time in milliseconds.  Note that because the
    76       * header has the granularity of one second, the value will get truncated to the nearest second that does not
    77       * exceed the provided value.
    78       * <p/>
    79       * This will also set the Expires header to a date in the past.  This forces clients to revalidate the cache each
    80       * time.
    81       *
    82       * @param response
    83       * @param lastModifiedTimeMillis
    84       */
    85      public static void setLastModifiedHeader(HttpServletResponse response, long lastModifiedTimeMillis) {
                 /* 
    P/P           *  Method: void setLastModifiedHeader(HttpServletResponse, long)
                  * 
                  *  Preconditions:
                  *    response != null
                  */
    86          response.setDateHeader("Last-Modified", lastModifiedTimeMillis);
    87          // Force clients to revalidate each time
    88          // See RFC 2616 (HTTP 1.1 spec) secs 14.21, 13.2.1
    89          response.setDateHeader("Expires", 0);
    90          // We may also want this (See 13.2.1 and 14.9.4)
    91          // response.setHeader("Cache-Control","must-revalidate");
    92      }
    93  }