SimpleDateFormat.java

package com.gwt.ui.client;
 
import java.util.Date;

public class SimpleDateFormat {
    private static final String TOKEN_DAY_OF_WEEK = "E";
    private static final String TOKEN_DAY_OF_MONTH = "d";
    private static final String TOKEN_MONTH = "M";
    private static final String TOKEN_YEAR = "y";
    private static final String TOKEN_HOUR_12 = "h";
    private static final String TOKEN_HOUR_24 = "H";
    private static final String TOKEN_MINUTE = "m";
    private static final String TOKEN_SECOND = "s";
    private static final String TOKEN_AM_PM = "a";
    private static final String AM = "AM";
    private static final String PM = "PM";
    private static final String[] SUPPORTED_TOKEN = new String[] {
        TOKEN_DAY_OF_WEEK, TOKEN_DAY_OF_MONTH, TOKEN_MONTH, TOKEN_YEAR, TOKEN_HOUR_12, TOKEN_HOUR_24, TOKEN_MINUTE, TOKEN_SECOND, TOKEN_AM_PM
    };
    
    private static final String[] MONTH_LONG = {
        "January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"
    };
    private static final String[] MONTH_SHORT = {
        "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sept", "Oct", "Nov", "Dec"
    };
    private static final String[] WEEKDAY_LONG = {
        "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"
    };
    private static final String[] WEEKDAY_SHORT = {
        "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
    };
    private String format;
    
    public SimpleDateFormat(String pattern) {
        
        format = pattern;
    }
    
    public String format(Date date) {
        String f = "";
        if (format != null && format.length() > 0) {
            String lastTokenType = null;
            String currentToken = "";
            for (int i = 0; i < format.length(); i++) {
                String thisChar = format.substring(i, i + 1);
                
                String currentTokenType = supported(thisChar);
                
                if (currentTokenType.equals(lastTokenType) || i == 0) {
                    currentToken += thisChar;
                    lastTokenType = currentTokenType;
                } else {
                    if ("".equals(lastTokenType))
                        f += currentToken;
                    else
                        f += handleToken(currentToken, date);
                    currentToken = thisChar;
                    lastTokenType = currentTokenType;
                }
            }
            if ("".equals(lastTokenType))
                f += currentToken;
            else
                f += handleToken(currentToken, date);
        }
        return f;
    }
    
    private String supported(String thisChar) {
        
        for (int i = 0; i < SUPPORTED_TOKEN.length; i++) {
            if (SUPPORTED_TOKEN[i].equals(thisChar))
                return thisChar;
        }
        return "";
    }
    
    /***
     * takes a date format string and returns the formatted portion of the date. For instance if the token is MMMM then
     * the full month name is returned.
     * 
     * @param token date format token
     * @param date date to format
     * @return formatted portion of the date
     */
    @SuppressWarnings("deprecation")
    private String handleToken(String token, Date date) {
        String response = token;
        String tc = token.substring(0, 1);  
        if (TOKEN_DAY_OF_WEEK.equals(tc)) {
            if (token.length() > 3)
                response = WEEKDAY_LONG[date.getDay()];
            else
                response = WEEKDAY_SHORT[date.getDay()];
        } else if (TOKEN_DAY_OF_MONTH.equals(tc)) {
            if (token.length() == 1)
                response = Integer.toString(date.getDay());
            else
                response = twoCharDateField(date.getDay());
        } else if (TOKEN_MONTH.equals(tc)) {
            switch (token.length()) {
                case 1:
                    response = Integer.toString(date.getMonth() + 1);
                    break;
                case 2:
                    response = twoCharDateField(date.getMonth() + 1);
                    break;
                case 3:
                    response = MONTH_SHORT[date.getMonth()];
                    break;
                default:
                    response = MONTH_LONG[date.getMonth()];
                    break;
            }
        } else if (TOKEN_YEAR.equals(tc)) {
            if (token.length() > 2)
                response = Integer.toString(date.getYear() + 1900);
            else
                response = twoCharDateField(date.getYear());
        } else if (TOKEN_HOUR_12.equals(tc)) {
            int h = date.getHours();
            if (h == 0)
                h = 12;
            else if (h > 12)
                h -= 12;
            if (token.length() > 1)
                response = twoCharDateField(h);
            else
                response = Integer.toString(h);
        } else if (TOKEN_HOUR_24.equals(tc)) {
            if (token.length() > 1)
                response = twoCharDateField(date.getHours());
            else
                response = Integer.toString(date.getHours());
        } else if (TOKEN_MINUTE.equals(tc)) {
            if (token.length() > 1)
                response = twoCharDateField(date.getMinutes());
            else
                response = Integer.toString(date.getMinutes());
        } else if (TOKEN_SECOND.equals(tc)) {
            if (token.length() > 1)
                response = twoCharDateField(date.getSeconds());
            else
                response = Integer.toString(date.getSeconds());
        } else if (TOKEN_AM_PM.equals(tc)) {
            int hour = date.getHours();
            if (hour > 11)
                response = PM;
            else
                response = AM;
        }
        return response;
    }
    
    /***
     * This is basically just a sneaky way to guarantee that our 1 or 2 digit numbers come out as a 2 character string.
     * we add an arbitrary number larger than 100, convert this new number to a string, then take the right most 2 characters.
     * 
     * @param num
     * @return
     */
    private String twoCharDateField(int num) {
        String res = Integer.toString(num + 1900);
        res = res.substring(res.length() - 2);
        return res;
    }
}