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 }