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