如何通过使用DecimalFormat将代表百分比，货币的数字值转换为字符串并返回BigDecimal

Question

Hi I'd like know how to format BigDecimal representing numbers,percents,moneys,integers to String in Locales and from String back to BigDecimal. I'm using DecimalFormat which is powerful, but I'm not sure how to use conversion to exact type in default user locales. I first time use this:

DecimalFormat.getCurrencyInstance().format( obj );
DecimalFormat.getCurrencyInstance().parse( source );

But with large numbers its misrepresents their value. So i find something and get this:

DecimalFormat decimalFormat = new DecimalFormat();
decimalFormat.setParseBigDecimal( true );
BigDecimal bd = ( BigDecimal ) decimalFormat.parse( value );

But how to combine these thinks. I probably need set to DecimalFormat some pattern which is used in NumberFormat.get???instance(), but I don't know how and if isn't get some strange behavior.

So Please someone who has experience with this can you help me? Thanks Pavel

Answer 1

I think your best bet is to assume that getCurrencyInstace() returns a DecimalFormat , which it probably does in all of the "important" locales. To be safe you could employ instanceof :

public static BigDecimal parseCurrencyPrecise (String value)
{
    NumberFormat  format = NumberFormat.getCurrencyInstance ();
    if (format instanceof DecimalFormat)
        ((DecimalFormat) format).setParseBigDecimal (true);

    Number  result = format.parse (value);
    if (result instanceof BigDecimal)
        return (BigDecimal) result;
    else {
        // Oh well...
        return new BigDecimal (result.doubleValue ());
    }
}

In our application we basically do the same for something different where you'd need SimpleDateFormat , but only have DateFormat in general case.

Answer 2

After a while a write this. It's seems to be working, but I'm not sure if it will work correctly on all Times. Maybe it helps someone else. I also hope that it does not violate any license).

import java.math.BigDecimal;
import java.text.DecimalFormat;
import java.text.DecimalFormatSymbols;
import java.text.ParseException;
import java.util.Currency;
import java.util.Locale;

import com.ibm.icu.impl.ICUResourceBundle;
import com.ibm.icu.text.NumberFormat;
import com.ibm.icu.util.UResourceBundle;

public class NumericHelper {

    public static BigDecimal parseStringToBigDecimal( String value, DecimalFormat decimalFormat ) throws ParseException {
        decimalFormat.setParseBigDecimal( true );
        return ( BigDecimal ) decimalFormat.parse( value );
    }

    /**
     * Extracted code from {@link NumberFormat#getPattern()} and
     * {@link java.text.NumberFormat#getInstance(Locale desiredLocale, int choice)} with some
     * modifications to get DecimalFormat with good Pattern
     * 
     * @param choice is static values from class {@link NumberFormat} eg
     *            {@link NumberFormat#INTEGERSTYLE}
     */
    public static DecimalFormat getDecimalFormatWithPattern( Locale desiredLocale, int choice ) {
        ICUResourceBundle rb = ( ICUResourceBundle ) UResourceBundle.getBundleInstance( ICUResourceBundle.ICU_BASE_NAME, desiredLocale );
        String[] numberPatterns = rb.getStringArray( "NumberPatterns" );

        DecimalFormatSymbols symbols = DecimalFormatSymbols.getInstance( desiredLocale );
        int entry = ( choice == NumberFormat.INTEGERSTYLE ) ? NumberFormat.NUMBERSTYLE : choice;
        DecimalFormat format = new DecimalFormat( numberPatterns[entry], symbols );

        if ( choice == NumberFormat.INTEGERSTYLE ) {
            format.setMaximumFractionDigits( 0 );
            format.setDecimalSeparatorAlwaysShown( false );
            format.setParseIntegerOnly( true );
        }
        else if ( choice == NumberFormat.CURRENCYSTYLE ) {
            adjustForCurrencyDefaultFractionDigits( format );
        }

        return format;
    }

    /**
     * Extracted from {@link DecimalFormat#adjustForCurrencyDefaultFractionDigits()} because it can
     * not be called
     */
    protected static void adjustForCurrencyDefaultFractionDigits( DecimalFormat decimalFormat ) {
        DecimalFormatSymbols symbols = decimalFormat.getDecimalFormatSymbols();

        Currency currency = symbols.getCurrency();
        if ( currency == null ) {
            try {
                currency = Currency.getInstance( symbols.getInternationalCurrencySymbol() );
            }
            catch ( IllegalArgumentException e ) {
            }
        }
        if ( currency != null ) {
            int digits = currency.getDefaultFractionDigits();
            if ( digits != -1 ) {
                int oldMinDigits = decimalFormat.getMinimumFractionDigits();
                // Common patterns are "#.##", "#.00", "#".
                // Try to adjust all of them in a reasonable way.
                if ( oldMinDigits == decimalFormat.getMaximumFractionDigits() ) {
                    decimalFormat.setMinimumFractionDigits( digits );
                    decimalFormat.setMaximumFractionDigits( digits );
                }
                else {
                    decimalFormat.setMinimumFractionDigits( Math.min( digits, oldMinDigits ) );
                    decimalFormat.setMaximumFractionDigits( digits );
                }
            }
        }
    }
}

After a next other time I figured that methods it its descendant classes ( ). I'm not sure how this can work, but it works. In the code is moment, that trying to get format from LocaleServiceProviderPool so I believe that it also returns DecimalFormat, if it does, thats no problem if doesnt, . In code what I write is this part omitted