1   /*
    2    * $HeadURL: https://svn.apache.org/repos/asf/httpcomponents/httpcore/tags/4.0.1/httpcore/src/main/java/org/apache/http/protocol/HttpDateGenerator.java $
    3    * $Revision: 744532 $
    4    * $Date: 2009-02-14 18:12:18 +0100 (Sat, 14 Feb 2009) $
    5    *
    6    * ====================================================================
    7    * Licensed to the Apache Software Foundation (ASF) under one
    8    * or more contributor license agreements.  See the NOTICE file
    9    * distributed with this work for additional information
   10    * regarding copyright ownership.  The ASF licenses this file
   11    * to you under the Apache License, Version 2.0 (the
   12    * "License"); you may not use this file except in compliance
   13    * with the License.  You may obtain a copy of the License at
   14    *
   15    *   http://www.apache.org/licenses/LICENSE-2.0
   16    *
   17    * Unless required by applicable law or agreed to in writing,
   18    * software distributed under the License is distributed on an
   19    * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
   20    * KIND, either express or implied.  See the License for the
   21    * specific language governing permissions and limitations
   22    * under the License.
   23    * ====================================================================
   24    *
   25    * This software consists of voluntary contributions made by many
   26    * individuals on behalf of the Apache Software Foundation.  For more
   27    * information on the Apache Software Foundation, please see
   28    * <http://www.apache.org/>.
   29    *
   30    */
   31   
   32   package org.apache.http.protocol;
   33   
   34   import java.text.DateFormat;
   35   import java.text.SimpleDateFormat;
   36   import java.util.Date;
   37   import java.util.Locale;
   38   import java.util.TimeZone;
   39   
   40   
   41   /**
   42    * Generates a date in the format required by the HTTP protocol.
   43    *
   44    *
   45    * @version $Revision: 744532 $
   46    * 
   47    * @since 4.0
   48    */
   49   public class HttpDateGenerator {
   50   
   51       /** Date format pattern used to generate the header in RFC 1123 format. */
   52       public static final
   53           String PATTERN_RFC1123 = "EEE, dd MMM yyyy HH:mm:ss zzz";
   54   
   55       /** The time zone to use in the date header. */
   56       public static final TimeZone GMT = TimeZone.getTimeZone("GMT");
   57   
   58   
   59       private final DateFormat dateformat;
   60       
   61       private long dateAsLong = 0L;
   62       private String dateAsText = null;
   63   
   64       public HttpDateGenerator() {
   65           super();
   66           this.dateformat = new SimpleDateFormat(PATTERN_RFC1123, Locale.US);
   67           this.dateformat.setTimeZone(GMT);
   68       }
   69       
   70       public synchronized String getCurrentDate() {
   71           long now = System.currentTimeMillis();
   72           if (now - this.dateAsLong > 1000) {
   73               // Generate new date string
   74               this.dateAsText = this.dateformat.format(new Date(now));
   75               this.dateAsLong = now;
   76           }
   77           return this.dateAsText;
   78       }
   79       
   80   }