src/main/java/com/fasterxml/jackson/databind/util/ISO8601DateFormat.java

package com.fasterxml.jackson.databind.util;

import java.text.*;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;

/**
 * Provide a fast thread-safe formatter/parser DateFormat for ISO8601 dates ONLY.
 * It was mainly done to be used with Jackson JSON Processor.
 * <p/>
 * Watch out for clone implementation that returns itself.
 * <p/>
 * All other methods but parse and format and clone are undefined behavior.
 *
 * @see ISO8601Utils
 */
public class ISO8601DateFormat extends DateFormat
{
    private static final long serialVersionUID = 1L;

    // those classes are to try to allow a consistent behavior for hascode/equals and other methods
    private static Calendar CALENDAR = new GregorianCalendar();
    private static NumberFormat NUMBER_FORMAT = new DecimalFormat();

    public ISO8601DateFormat() {
        this.numberFormat = NUMBER_FORMAT;
        this.calendar = CALENDAR;
    }

    @Override
    public StringBuffer format(Date date, StringBuffer toAppendTo, FieldPosition fieldPosition) {
        String value = ISO8601Utils.format(date);
        toAppendTo.append(value);
        return toAppendTo;
    }

    @Override
    public Date parse(String source, ParsePosition pos) {
        // index must be set to other than 0, I would swear this requirement is not there in
        // some version of jdk 6.
        /* 03-Nov-2013, tatu: I can't see this having any direct effect
         *   here... I am guessing it marks things as consumed but why?
         */
        pos.setIndex(source.length());
        return ISO8601Utils.parse(source);
    }

    @Override
    public Object clone() {
        /* Jackson calls clone for every call. Since this instance is
         * immutable (and hence thread-safe)
         * we can just return this instance
         */
        return this;
    }

    @Override
    public String toString() { return getClass().getName(); }
}