http://www.joda.org/joda-time/: Date and time library to replace JDK date handling (Joda.org) 
/*
 *  Copyright 2001-2005 Stephen Colebourne
 *
 *  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 org.joda.time.format;


Factory that creates instances of PeriodFormatter for the ISO8601 standard.

 Period formatting is performed by the PeriodFormatter class. Three classes provide factory methods to create formatters, and this is one. The others are PeriodFormat and PeriodFormatterBuilder. 

ISOPeriodFormat is thread-safe and immutable, and the formatters it
returns are as well.

Author:Brian S O'Neill
See Also:
Since:1.0
/**
 * Factory that creates instances of PeriodFormatter for the ISO8601 standard.
 * <p>
 * Period formatting is performed by the {@link PeriodFormatter} class.
 * Three classes provide factory methods to create formatters, and this is one.
 * The others are {@link PeriodFormat} and {@link PeriodFormatterBuilder}.
 * <p>
 * ISOPeriodFormat is thread-safe and immutable, and the formatters it
 * returns are as well.
 *
 * @author Brian S O'Neill
 * @since 1.0
 * @see PeriodFormat
 * @see PeriodFormatterBuilder
 */
public class ISOPeriodFormat {

    
Cache of standard format. 
/** Cache of standard format. */
    private static PeriodFormatter cStandard;
    
Cache of alternate months format. 
/** Cache of alternate months format. */
    private static PeriodFormatter cAlternate;
    
Cache of alternate extended months format. 
/** Cache of alternate extended months format. */
    private static PeriodFormatter cAlternateExtended;
    
Cache of alternate weeks format. 
/** Cache of alternate weeks format. */
    private static PeriodFormatter cAlternateWithWeeks;
    
Cache of alternate extended weeks format. 
/** Cache of alternate extended weeks format. */
    private static PeriodFormatter cAlternateExtendedWihWeeks;

    
Constructor.

Since:1.1 (previously private)
/**
     * Constructor.
     *
     * @since 1.1 (previously private)
     */
    protected ISOPeriodFormat() {
        super();
    }

    //-----------------------------------------------------------------------
    
The standard ISO format - PyYmMwWdDThHmMsS.
Milliseconds are not output.
Note that the ISO8601 standard actually indicates weeks should not
be shown if any other field is present and vice versa.

Returns:the formatter
/**
     * The standard ISO format - PyYmMwWdDThHmMsS.
     * Milliseconds are not output.
     * Note that the ISO8601 standard actually indicates weeks should not
     * be shown if any other field is present and vice versa.
     * 
     * @return the formatter
     */
    public static PeriodFormatter standard() {
        if (cStandard == null) {
            cStandard = new PeriodFormatterBuilder()
                .appendLiteral("P")
                .appendYears()
                .appendSuffix("Y")
                .appendMonths()
                .appendSuffix("M")
                .appendWeeks()
                .appendSuffix("W")
                .appendDays()
                .appendSuffix("D")
                .appendSeparatorIfFieldsAfter("T")
                .appendHours()
                .appendSuffix("H")
                .appendMinutes()
                .appendSuffix("M")
                .appendSecondsWithOptionalMillis()
                .appendSuffix("S")
                .toFormatter();
        }
        return cStandard;
    }

    
The alternate ISO format, PyyyymmddThhmmss, which excludes weeks.


Even if weeks are present in the period, they are not output.
Fractional seconds (milliseconds) will appear if required.

Returns:the formatter
/**
     * The alternate ISO format, PyyyymmddThhmmss, which excludes weeks.
     * <p>
     * Even if weeks are present in the period, they are not output.
     * Fractional seconds (milliseconds) will appear if required.
     * 
     * @return the formatter
     */
    public static PeriodFormatter alternate() {
        if (cAlternate == null) {
            cAlternate = new PeriodFormatterBuilder()
                .appendLiteral("P")
                .printZeroAlways()
                .minimumPrintedDigits(4)
                .appendYears()
                .minimumPrintedDigits(2)
                .appendMonths()
                .appendDays()
                .appendSeparatorIfFieldsAfter("T")
                .appendHours()
                .appendMinutes()
                .appendSecondsWithOptionalMillis()
                .toFormatter();
        }
        return cAlternate;
    }

    
The alternate ISO format, Pyyyy-mm-ddThh:mm:ss, which excludes weeks.


Even if weeks are present in the period, they are not output.
Fractional seconds (milliseconds) will appear if required.

Returns:the formatter
/**
     * The alternate ISO format, Pyyyy-mm-ddThh:mm:ss, which excludes weeks.
     * <p>
     * Even if weeks are present in the period, they are not output.
     * Fractional seconds (milliseconds) will appear if required.
     * 
     * @return the formatter
     */
    public static PeriodFormatter alternateExtended() {
        if (cAlternateExtended == null) {
            cAlternateExtended = new PeriodFormatterBuilder()
                .appendLiteral("P")
                .printZeroAlways()
                .minimumPrintedDigits(4)
                .appendYears()
                .appendSeparator("-")
                .minimumPrintedDigits(2)
                .appendMonths()
                .appendSeparator("-")
                .appendDays()
                .appendSeparatorIfFieldsAfter("T")
                .appendHours()
                .appendSeparator(":")
                .appendMinutes()
                .appendSeparator(":")
                .appendSecondsWithOptionalMillis()
                .toFormatter();
        }
        return cAlternateExtended;
    }

    
The alternate ISO format, PyyyyWwwddThhmmss, which excludes months.


Even if months are present in the period, they are not output.
Fractional seconds (milliseconds) will appear if required.

Returns:the formatter
/**
     * The alternate ISO format, PyyyyWwwddThhmmss, which excludes months.
     * <p>
     * Even if months are present in the period, they are not output.
     * Fractional seconds (milliseconds) will appear if required.
     * 
     * @return the formatter
     */
    public static PeriodFormatter alternateWithWeeks() {
        if (cAlternateWithWeeks == null) {
            cAlternateWithWeeks = new PeriodFormatterBuilder()
                .appendLiteral("P")
                .printZeroAlways()
                .minimumPrintedDigits(4)
                .appendYears()
                .minimumPrintedDigits(2)
                .appendPrefix("W")
                .appendWeeks()
                .appendDays()
                .appendSeparatorIfFieldsAfter("T")
                .appendHours()
                .appendMinutes()
                .appendSecondsWithOptionalMillis()
                .toFormatter();
        }
        return cAlternateWithWeeks;
    }

    
The alternate ISO format, Pyyyy-Www-ddThh:mm:ss, which excludes months.


Even if months are present in the period, they are not output.
Fractional seconds (milliseconds) will appear if required.

Returns:the formatter
/**
     * The alternate ISO format, Pyyyy-Www-ddThh:mm:ss, which excludes months.
     * <p>
     * Even if months are present in the period, they are not output.
     * Fractional seconds (milliseconds) will appear if required.
     * 
     * @return the formatter
     */
    public static PeriodFormatter alternateExtendedWithWeeks() {
        if (cAlternateExtendedWihWeeks == null) {
            cAlternateExtendedWihWeeks = new PeriodFormatterBuilder()
                .appendLiteral("P")
                .printZeroAlways()
                .minimumPrintedDigits(4)
                .appendYears()
                .appendSeparator("-")
                .minimumPrintedDigits(2)
                .appendPrefix("W")
                .appendWeeks()
                .appendSeparator("-")
                .appendDays()
                .appendSeparatorIfFieldsAfter("T")
                .appendHours()
                .appendSeparator(":")
                .appendMinutes()
                .appendSeparator(":")
                .appendSecondsWithOptionalMillis()
                .toFormatter();
        }
        return cAlternateExtendedWihWeeks;
    }

}