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 org.apache.http.annotation.ThreadingBehavior;
31 import org.apache.http.annotation.Contract;
32
33 import java.text.DateFormat;
34 import java.text.SimpleDateFormat;
35 import java.util.Date;
36 import java.util.Locale;
37 import java.util.TimeZone;
38
39 /**
40 * Generates a date in the format required by the HTTP protocol.
41 *
42 * @since 4.0
43 */
44 @Contract(threading = ThreadingBehavior.SAFE)
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 private final DateFormat dateformat;
55 private long dateAsLong = 0L;
56 private String dateAsText = null;
57
58 public HttpDateGenerator() {
59 super();
60 this.dateformat = new SimpleDateFormat(PATTERN_RFC1123, Locale.US);
61 this.dateformat.setTimeZone(GMT);
62 }
63
64 public synchronized String getCurrentDate() {
65 final long now = System.currentTimeMillis();
66 if (now - this.dateAsLong > 1000) {
67 // Generate new date string
68 this.dateAsText = this.dateformat.format(new Date(now));
69 this.dateAsLong = now;
70 }
71 return this.dateAsText;
72 }
73
74 }