1/*
2 * $HeadURL: http://svn.apache.org/repos/asf/httpcomponents/httpcore/trunk/module-main/src/main/java/org/apache/http/protocol/HttpDateGenerator.java $
3 * $Revision: 548066 $
4 * $Date: 2007-06-17 09:51:55 -0700 (Sun, 17 Jun 2007) $
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
32package org.apache.http.protocol;
33
34import java.text.DateFormat;
35import java.text.SimpleDateFormat;
36import java.util.Date;
37import java.util.Locale;
38import java.util.TimeZone;
39
40
41/**
42 * Generates a date in the format required by the HTTP protocol.
43 *
44 * @author <a href="mailto:oleg at ural.ru">Oleg Kalnichevski</a>
45 *
46 * @version $Revision: 548066 $
47 *
48 * @since 4.0
49 */
50public class HttpDateGenerator {
51
52    /** Date format pattern used to generate the header in RFC 1123 format. */
53    public static final
54        String PATTERN_RFC1123 = "EEE, dd MMM yyyy HH:mm:ss zzz";
55
56    /** The time zone to use in the date header. */
57    public static final TimeZone GMT = TimeZone.getTimeZone("GMT");
58
59
60    private final DateFormat dateformat;
61
62    private long dateAsLong = 0L;
63    private String dateAsText = null;
64
65    public HttpDateGenerator() {
66        super();
67        this.dateformat = new SimpleDateFormat(PATTERN_RFC1123, Locale.US);
68        this.dateformat.setTimeZone(GMT);
69    }
70
71    public synchronized String getCurrentDate() {
72        long now = System.currentTimeMillis();
73        if (now - this.dateAsLong > 1000) {
74            // Generate new date string
75            this.dateAsText = this.dateformat.format(new Date(now));
76            this.dateAsLong = now;
77        }
78        return this.dateAsText;
79    }
80
81}
82