HttpDateParser.java

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 * to you under the Apache License, Version 2.0 (the
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package org.apache.wink.common.internal.utils;

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

/**
 * Parser of date format used HTTP spec.
 */
public final class HttpDateParser {

    private static final String   RFC_1123_DATE_FORMAT = "EEE, dd MMM yyyy HH:mm:ss zzz"; //$NON-NLS-1$
    private static final String   RFC_1036_DATE_FORMAT = "EEEE, dd-MMM-yy HH:mm:ss zzz"; //$NON-NLS-1$
    private static final String   ANSIC_DATE_FORMAT    = "EEE MMM d HH:mm:ss yyyy"; //$NON-NLS-1$
    private static final TimeZone tz                   = TimeZone.getTimeZone("GMT"); //$NON-NLS-1$

    // no instances
    private HttpDateParser() {
    }

    /**
     * Converts HTTP date to Java Date.
     * 
     * @param date not <code>null</code>
     * @return Java Date
     * @throws IllegalArgumentException if parsing fails
     */
    public static Date parseHttpDate(String date) {
        
        // http://www.squid-cache.org/mail-archive/squid-users/200307/0122.html
        // Some IE browsers send If-Modified-Since header with a length extension such as: Thu, 01 Sep 2011 00:48:38 GMT; length=347987
        int index = date.indexOf(';');
        if (index != -1) {
            date = date.substring(0, index).trim();
        }

        int indexOfComma = date.indexOf(',');
        try {
            if (indexOfComma == -1) { // choosed format base on comma position
                return createSimpleDateFormat(ANSIC_DATE_FORMAT).parse(date);
            } else if (indexOfComma == 3) {
                return createSimpleDateFormat(RFC_1123_DATE_FORMAT).parse(date);
            } else {
                return createSimpleDateFormat(RFC_1036_DATE_FORMAT).parse(date);
            }
        } catch (ParseException e) {
            throw new IllegalArgumentException(e);
        }
    }

    private static SimpleDateFormat createSimpleDateFormat(String format) {
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat(format, Locale.US);
        simpleDateFormat.setTimeZone(tz);
        return simpleDateFormat;
    }

    /**
     * Converts Java Data to HTTP date string.
     * 
     * @param date Java Date
     * @return the HTTP date string
     */
    public static String toHttpDate(Date date) {
        return createSimpleDateFormat(RFC_1123_DATE_FORMAT).format(date);
    }
}