Formatter that caches formatted date information : Date Format « Data Type « Java Tutorial

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 * 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
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * See the License for the specific language governing permissions and
 * limitations under the License.

import java.util.Date;

import java.text.DateFormat;
import java.text.FieldPosition;
import java.text.ParsePosition;
import java.text.SimpleDateFormat;

 * Fast date formatter that caches recently formatted date information
 * and uses it to avoid too-frequent calls to the underlying
 * formatter.  Note: breaks fieldPosition param of format(Date,
 * StringBuffer, FieldPosition).  If you care about the field
 * position, call the underlying DateFormat directly.
 * @author Stan Bailes
 * @author Alex Chaffee
public class FastDateFormat extends DateFormat {
    DateFormat    df;
    long          lastSec = -1;
    StringBuffer  sb      = new StringBuffer();
    FieldPosition fp      = new FieldPosition(DateFormat.MILLISECOND_FIELD);

    public FastDateFormat(DateFormat df) {
        this.df = df;

    public Date parse(String text, ParsePosition pos) {
        return df.parse(text, pos);

     * Note: breaks functionality of fieldPosition param. Also:
     * there's a bug in SimpleDateFormat with "S" and "SS", use "SSS"
     * instead if you want a msec field.
    public StringBuffer format(Date date, StringBuffer toAppendTo,
                               FieldPosition fieldPosition) {
        long dt = date.getTime();
        long ds = dt / 1000;
        if (ds != lastSec) {
            df.format(date, sb, fp);
            lastSec = ds;
        } else {
            // munge current msec into existing string
            int ms = (int)(dt % 1000);
            int pos = fp.getEndIndex();
            int begin = fp.getBeginIndex();
            if (pos > 0) {
                if (pos > begin)
                    sb.setCharAt(--pos, Character.forDigit(ms % 10, 10));
                ms /= 10;
                if (pos > begin)
                    sb.setCharAt(--pos, Character.forDigit(ms % 10, 10));
                ms /= 10;
                if (pos > begin)
                    sb.setCharAt(--pos, Character.forDigit(ms % 10, 10));
        return toAppendTo;

    public static void main(String[] args) {
        String format = "yyyy-MM-dd HH:mm:ss.SSS";
        if (args.length > 0)
            format = args[0];
        SimpleDateFormat sdf = new SimpleDateFormat(format);
        FastDateFormat fdf = new FastDateFormat(sdf);
        Date d = new Date();

        d.setTime(1); System.out.println(fdf.format(d) + "\t" + sdf.format(d));
        d.setTime(20); System.out.println(fdf.format(d) + "\t" + sdf.format(d));
        d.setTime(500); System.out.println(fdf.format(d) + "\t" + sdf.format(d));
        d.setTime(543); System.out.println(fdf.format(d) + "\t" + sdf.format(d));
        d.setTime(999); System.out.println(fdf.format(d) + "\t" + sdf.format(d));
        d.setTime(1050); System.out.println(fdf.format(d) + "\t" + sdf.format(d));
        d.setTime(2543); System.out.println(fdf.format(d) + "\t" + sdf.format(d));
        d.setTime(12345); System.out.println(fdf.format(d) + "\t" + sdf.format(d));
        d.setTime(12340); System.out.println(fdf.format(d) + "\t" + sdf.format(d));

        final int reps = 100000;
            long start = System.currentTimeMillis();
            for (int i = 0; i < reps; i++) {
            long elap = System.currentTimeMillis() - start;
            System.out.println("fast: " + elap + " elapsed");
            long start = System.currentTimeMillis();
            for (int i = 0; i < reps; i++) {
            long elap = System.currentTimeMillis() - start;
            System.out.println("slow: " + elap + " elapsed");

2.41.Date Format
2.41.1.Date Parsing and Formatting with DateFormat
2.41.2.Parsing the Time Using a Custom Format
2.41.3.Parse with a custom format
2.41.4.Parse with a default format
2.41.5.Parse string date value input with SimpleDateFormat('dd-MMM-yy')
2.41.6.Parse a date and time
2.41.7.Parse string date value input with SimpleDateFormat('E, dd MMM yyyy HH:mm:ss Z')
2.41.8.Parse string date value with default format: DateFormat.getDateInstance(DateFormat.DEFAULT)
2.41.10.Formatting String Symbols for SimpleDateFormat
2.41.11.SimpleDateFormat: hh:mm:ss, dd MMM yyyy hh:mm:ss zzz, E MMM dd yyyy
2.41.12.Simply format a date as YYYYMMDD
2.41.13.Express a duration in term of HH:MM:SS
2.41.14.Date Format with SimpleDateFormat
2.41.15.Demonstrate date formats with different DateFormat constants
2.41.16.Demonstrate time formats.
2.41.18.print out the current date and time
2.41.19.Date Era change
2.41.20.Format Date with System.out.format
2.41.22.Formatting Dates and Times
2.41.23.Four different date formats for four countries: US, UK, GERMANY, FRANCE
2.41.24.Various Date formatVarious Date format
2.41.25.Display date with day name in a short format
2.41.26.Display date with a short day and month name
2.41.27.Format a date into dd/mm/yyyy
2.41.28.Format current date and time with the SimpleDateFormat: dd/MM/yyyy
2.41.29.Format current date and time with the SimpleDateFormat: HH:mm:ss
2.41.30.Formatting Symbols for SimpleDateFormat
2.41.31.Formatting the Time Using a Custom Format
2.41.32.Change date formatting symbols
2.41.33.Get a List of Short Month Names
2.41.34.Get a List of Weekday Names
2.41.35.Get a List of Short Weekday Names
2.41.36.Time in 12-hour format
2.41.37.Time in 24-hour format
2.41.38.Date and time with month
2.41.39.Date and time with day and month fully spelled-out
2.41.40.Output current time: %tc
2.41.41.Formatter that caches formatted date information
2.41.42.RFC date format
2.41.43.A formatter that formats dates to show the elapsed time relative to some base date.