解析各种格式的日期是一个挑战，下面贴出一个比较完善的解析各种日期时间格式的Java类源代码：

/*
 * Copyright 2004 Sun Microsystems, Inc.
 *
 * Licensed 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.
 *
 */
package net.sf.flock.parser;

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

/**
 * A helper class that parses Dates out of Strings with date time in RFC822 and W3CDateTime
 * formats plus the variants Atom (0.3) and RSS (0.9, 0.91, 0.92, 0.93, 0.94, 1.0 and 2.0)
 * specificators added to those formats.
 * <p/>
 * It uses the JDK java.text.SimpleDateFormat class attemtping the parse using a mask for
 * each one of the possible formats.
 * <p/>
 *
 * @author Alejandro Abdelnur
 *
 */
public class DateParser {

    private static String[] ADDITIONAL_MASKS;

    static {
//        ADDITIONAL_MASKS = PropertiesLoader.getPropertiesLoader().getTokenizedProperty("datetime.extra.masks","|");
        ADDITIONAL_MASKS=new String[]{"HH:mm yyyy/MM/dd","yyyy-MM-dd HH:mm:ss",
       "yyyy-MM-dd HH:mm"};
    }

    // order is like this because the SimpleDateFormat.parse does not fail with exception
    // if it can parse a valid date out of a substring of the full string given the mask
    // so we have to check the most complete format first, then it fails with exception
    private static final String[] RFC822_MASKS = {
            "EEE, dd MMM yy HH:mm:ss z",
            "EEE, dd MMM yy HH:mm z",
            "dd MMM yy HH:mm:ss z",
            "dd MMM yy HH:mm z"
        };



    // order is like this because the SimpleDateFormat.parse does not fail with exception
    // if it can parse a valid date out of a substring of the full string given the mask
    // so we have to check the most complete format first, then it fails with exception
    private static final String[] W3CDATETIME_MASKS = {
        "yyyy-MM-dd'T'HH:mm:ss.SSSz",
        "yyyy-MM-dd't'HH:mm:ss.SSSz",
        "yyyy-MM-dd'T'HH:mm:ss.SSS'Z'",
        "yyyy-MM-dd't'HH:mm:ss.SSS'z'",
        "yyyy-MM-dd'T'HH:mm:ssz",
        "yyyy-MM-dd't'HH:mm:ssz",
        "yyyy-MM-dd'T'HH:mm:ss'Z'",
        "yyyy-MM-dd't'HH:mm:ss'z'",
        "yyyy-MM-dd'T'HH:mmz",   // together with logic in the parseW3CDateTime they
        "yyyy-MM'T'HH:mmz",      // handle W3C dates without time forcing them to be GMT
        "yyyy'T'HH:mmz",         
        "yyyy-MM-dd't'HH:mmz",
        "yyyy-MM-dd'T'HH:mm'Z'",
        "yyyy-MM-dd't'HH:mm'z'",
        "yyyy-MM-dd",
        "yyyy-MM",
        "yyyy"
    };
   
   
   
      /**
   * The masks used to validate and parse the input to this Atom date.
   * These are a lot more forgiving than what the Atom spec allows. 
   * The forms that are invalid according to the spec are indicated.
   */
  private static final String[] masks = {
    "yyyy-MM-dd'T'HH:mm:ss.SSSz",
    "yyyy-MM-dd't'HH:mm:ss.SSSz",                         // invalid
    "yyyy-MM-dd'T'HH:mm:ss.SSS'Z'",
    "yyyy-MM-dd't'HH:mm:ss.SSS'z'",                       // invalid
    "yyyy-MM-dd'T'HH:mm:ssz",
    "yyyy-MM-dd't'HH:mm:ssz",                             // invalid
    "yyyy-MM-dd'T'HH:mm:ss'Z'",
    "yyyy-MM-dd't'HH:mm:ss'z'",                           // invalid
    "yyyy-MM-dd'T'HH:mmz",                                // invalid
    "yyyy-MM-dd't'HH:mmz",                                // invalid
    "yyyy-MM-dd'T'HH:mm'Z'",                              // invalid
    "yyyy-MM-dd't'HH:mm'z'",                              // invalid
    "yyyy-MM-dd",
    "yyyy-MM",
    "yyyy"
  };
   
   
   

    /**
     * Private constructor to avoid DateParser instances creation.
     */
    private DateParser() {
    }

    /**
     * Parses a Date out of a string using an array of masks.
     * <p/>
     * It uses the masks in order until one of them succedes or all fail.
     * <p/>
     *
     * @param masks array of masks to use for parsing the string
     * @param sDate string to parse for a date.
     * @return the Date represented by the given string using one of the given masks.
     * It returns <b>null</b> if it was not possible to parse the the string with any of the masks.
     *
     */
    private static Date parseUsingMask(String[] masks,String sDate) {
        sDate = (sDate!=null) ? sDate.trim() : null;
        ParsePosition pp = null;
        Date d = null;
        for (int i=0;d==null && i<masks.length;i++) {
            DateFormat df = new SimpleDateFormat(masks[i],Locale.US);
            //df.setLenient(false);
            df.setLenient(true);
            try {
                pp = new ParsePosition(0);
                d = df.parse(sDate,pp);
                if (pp.getIndex()!=sDate.length()) {
                    d = null;
                }
                //System.out.println("pp["+pp.getIndex()+"] s["+sDate+" m["+masks[i]+"] d["+d+"]");
            }
            catch (Exception ex1) {
                //System.out.println("s: "+sDate+" m: "+masks[i]+" d: "+null);
            }
        }
        return d;
    }

    /**
     * Parses a Date out of a String with a date in RFC822 format.
     * <p/>
     * It parsers the following formats:
     * <ul>
     *   <li>"EEE, dd MMM yyyy HH:mm:ss z"</li>
     *   <li>"EEE, dd MMM yyyy HH:mm z"</li>
     *   <li>"EEE, dd MMM yy HH:mm:ss z"</li>
     *   <li>"EEE, dd MMM yy HH:mm z"</li>
     *   <li>"dd MMM yyyy HH:mm:ss z"</li>
     *   <li>"dd MMM yyyy HH:mm z"</li>
     *   <li>"dd MMM yy HH:mm:ss z"</li>
     *   <li>"dd MMM yy HH:mm z"</li>
     * </ul>
     * <p/>
     * Refer to the java.text.SimpleDateFormat javadocs for details on the format of each element.
     * <p/>
     * @param sDate string to parse for a date.
     * @return the Date represented by the given RFC822 string.
     *         It returns <b>null</b> if it was not possible to parse the given string into a Date.
     *
     */
    public static Date parseRFC822(String sDate) {
        int utIndex = sDate.indexOf(" UT");
        if (utIndex>-1) {
            String pre = sDate.substring(0,utIndex);
            String post = sDate.substring(utIndex+3);
            sDate = pre + " GMT" + post;
        }
        return parseUsingMask(RFC822_MASKS,sDate);
    }


    /**
     * Parses a Date out of a String with a date in W3C date-time format.
     * <p/>
     * It parsers the following formats:
     * <ul>
     *   <li>"yyyy-MM-dd'T'HH:mm:ssz"</li>
     *   <li>"yyyy-MM-dd'T'HH:mmz"</li>
     *   <li>"yyyy-MM-dd"</li>
     *   <li>"yyyy-MM"</li>
     *   <li>"yyyy"</li>
     * </ul>
     * <p/>
     * Refer to the java.text.SimpleDateFormat javadocs for details on the format of each element.
     * <p/>
     * @param sDate string to parse for a date.
     * @return the Date represented by the given W3C date-time string.
     *         It returns <b>null</b> if it was not possible to parse the given string into a Date.
     *
     */
    public static Date parseW3CDateTime(String sDate) {
        // if sDate has time on it, it injects 'GTM' before de TZ displacement to
        // allow the SimpleDateFormat parser to parse it properly
        int tIndex = sDate.indexOf("T");
        if (tIndex>-1) {
            if (sDate.endsWith("Z")) {
                sDate = sDate.substring(0,sDate.length()-1)+"+00:00";
            }
            int tzdIndex = sDate.indexOf("+",tIndex);
            if (tzdIndex==-1) {
                tzdIndex = sDate.indexOf("-",tIndex);
            }
            if (tzdIndex>-1) {
                String pre = sDate.substring(0,tzdIndex);
                int secFraction = pre.indexOf(",");
                if (secFraction>-1) {
                    pre = pre.substring(0,secFraction);
                }
                String post = sDate.substring(tzdIndex);
                sDate = pre + "GMT" + post;
            }
        }
        else {
            sDate += "T00:00GMT";
        }
        return parseUsingMask(W3CDATETIME_MASKS,sDate);
    }


    /**
     * Parses a Date out of a String with a date in W3C date-time format or
     * in a RFC822 format.
     * <p>
     * @param sDate string to parse for a date.
     * @return the Date represented by the given W3C date-time string.
     *         It returns <b>null</b> if it was not possible to parse the given string into a Date.
     *
     * */
    public static Date parseDate(String sDate) {
        Date d = parseW3CDateTime(sDate);
        if (d==null) {
            d = parseRFC822(sDate);
            if (d==null && ADDITIONAL_MASKS.length>0) {
                d = parseUsingMask(ADDITIONAL_MASKS,sDate);
            }
        }
        return d;
    }

    /**
     * create a RFC822 representation of a date.
     * <p/>
     * Refer to the java.text.SimpleDateFormat javadocs for details on the format of each element.
     * <p/>
     * @param date Date to parse
     * @return the RFC822 represented by the given Date
     *         It returns <b>null</b> if it was not possible to parse the date.
     *
     */
    public static String formatRFC822(Date date) {
        SimpleDateFormat dateFormater = new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss 'GMT'",Locale.US);
        dateFormater.setTimeZone(TimeZone.getTimeZone("GMT"));
        return dateFormater.format(date);
    }

    /**
     * create a W3C Date Time representation of a date.
     * <p/>
     * Refer to the java.text.SimpleDateFormat javadocs for details on the format of each element.
     * <p/>
     * @param date Date to parse
     * @return the W3C Date Time represented by the given Date
     *         It returns <b>null</b> if it was not possible to parse the date.
     *
     */
    public static String formatW3CDateTime(Date date) {
        SimpleDateFormat dateFormater = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'",Locale.US);
        dateFormater.setTimeZone(TimeZone.getTimeZone("GMT"));
        return dateFormater.format(date);
    }
   
    public static void main(String[] args){
        DateParser p=new DateParser();
        System.out.println(p.parseDate("Sat, 27 Sep 2008 17:26:54 EDT"));
    }
}