/*
 * $HeadURL: http://svn.apache.org/repos/asf/httpcomponents/httpcore/trunk/module-main/src/main/java/org/apache/http/protocol/HttpDateGenerator.java $
 * $Revision: 548066 $
 * $Date: 2007-06-17 09:51:55 -0700 (Sun, 17 Jun 2007) $
 *
 * ====================================================================
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 *
 */

package org.apache.http.protocol;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Locale;
import java.util.TimeZone;


/**
 * Generates a date in the format required by the HTTP protocol.
 *
 * @author <a href="mailto:oleg at ural.ru">Oleg Kalnichevski</a>
 *
 * @version $Revision: 548066 $
 * 
 * @since 4.0
 */
public class HttpDateGenerator {

    /** Date format pattern used to generate the header in RFC 1123 format. */
    public static final
        String PATTERN_RFC1123 = "EEE, dd MMM yyyy HH:mm:ss zzz";

    /** The time zone to use in the date header. */
    public static final TimeZone GMT = TimeZone.getTimeZone("GMT");


    private final DateFormat dateformat;
    
    private long dateAsLong = 0L;
    private String dateAsText = null;

    public HttpDateGenerator() {
        super();
        this.dateformat = new SimpleDateFormat(PATTERN_RFC1123, Locale.US);
        this.dateformat.setTimeZone(GMT);
    }
    
    public synchronized String getCurrentDate() {
        long now = System.currentTimeMillis();
        if (now - this.dateAsLong > 1000) {
            // Generate new date string
            this.dateAsText = this.dateformat.format(new Date(now));
            this.dateAsLong = now;
        }
        return this.dateAsText;
    }
    
}