com.aspose.words

Example:

Document doc = new Document();
    DocumentBuilder builder = new DocumentBuilder(doc);
    FieldResultFormatter formatter = new FieldResultFormatter("$%d", "Date: %tb", "Item # %s:");
    doc.getFieldOptions().setResultFormatter(formatter);

    // Our field result formatter applies a custom format to newly created fields of three types of formats.
    // Field result formatters apply new formatting to fields as they are updated,
    // which happens as soon as we create them using this InsertField method overload.
    // 1 -  Numeric:
    builder.insertField(" = 2 + 3 \\# $###");

    Assert.assertEquals("$5", doc.getRange().getFields().get(0).getResult());
    Assert.assertEquals(1, formatter.countFormatInvocations(FieldResultFormatter.FormatInvocationType.NUMERIC));

    // 2 -  Date/time:
    builder.insertField("DATE \\@ \"d MMMM yyyy\"");

    Assert.assertTrue(doc.getRange().getFields().get(1).getResult().startsWith("Date: "));
    Assert.assertEquals(1, formatter.countFormatInvocations(FieldResultFormatter.FormatInvocationType.DATE_TIME));

    // 3 -  General:
    builder.insertField("QUOTE \"2\" \\* Ordinal");

    Assert.assertEquals("Item # 2:", doc.getRange().getFields().get(2).getResult());
    Assert.assertEquals(1, formatter.countFormatInvocations(FieldResultFormatter.FormatInvocationType.GENERAL));

    formatter.printFormatInvocations();
}

/// <summary>
/// When fields with formatting are updated, this formatter will override their formatting
/// with a custom format, while tracking every invocation.
/// </summary>
private static class FieldResultFormatter implements IFieldResultFormatter {
    public FieldResultFormatter(String numberFormat, String dateFormat, String generalFormat) {
        mNumberFormat = numberFormat;
        mDateFormat = dateFormat;
        mGeneralFormat = generalFormat;
    }

    public String formatNumeric(double value, String format) {
        if (mNumberFormat.isEmpty())
            return null;

        String newValue = String.format(mNumberFormat, (long) value);
        mFormatInvocations.add(new FormatInvocation(FormatInvocationType.NUMERIC, value, format, newValue));
        return newValue;
    }

    public String formatDateTime(Date value, String format, int calendarType) {
        if (mDateFormat.isEmpty())
            return null;

        String newValue = String.format(mDateFormat, value);
        mFormatInvocations.add(new FormatInvocation(FormatInvocationType.DATE_TIME, MessageFormat.format("{0} ({1})", value, calendarType), format, newValue));
        return newValue;
    }

    public String format(String value, int format) {
        return format((Object) value, format);
    }

    public String format(double value, int format) {
        return format((Object) value, format);
    }

    private String format(Object value, int format) {
        if (mGeneralFormat.isEmpty())
            return null;

        String newValue = String.format(mGeneralFormat, new DecimalFormat("#.####").format(value));
        mFormatInvocations.add(new FormatInvocation(FormatInvocationType.GENERAL, value, GeneralFormat.toString(format), newValue));
        return newValue;
    }

    public int countFormatInvocations(int formatInvocationType) {
        if (formatInvocationType == FormatInvocationType.ALL)
            return getFormatInvocations().size();

        return (int) IterableUtils.countMatches(getFormatInvocations(), i -> i.getFormatInvocationType() == formatInvocationType);
    }

    public void printFormatInvocations() {
        for (FormatInvocation f : getFormatInvocations())
            System.out.println(MessageFormat.format("Invocation type:\t{0}\n" +
                    "\tOriginal value:\t\t{1}\n" +
                    "\tOriginal format:\t{2}\n" +
                    "\tNew value:\t\t\t{3}\n", f.getFormatInvocationType(), f.getValue(), f.getOriginalFormat(), f.getNewValue()));
    }

    private final String mNumberFormat;
    private final String mDateFormat;
    private final String mGeneralFormat;

    private ArrayList<FormatInvocation> getFormatInvocations() {
        return mFormatInvocations;
    }

    private final ArrayList<FormatInvocation> mFormatInvocations = new ArrayList<>();

    private static class FormatInvocation {
        public int getFormatInvocationType() {
            return mFormatInvocationType;
        }

        private final int mFormatInvocationType;

        public Object getValue() {
            return mValue;
        }

        private final Object mValue;

        public String getOriginalFormat() {
            return mOriginalFormat;
        }

        private final String mOriginalFormat;

        public String getNewValue() {
            return mNewValue;
        }

        private final String mNewValue;

        public FormatInvocation(int formatInvocationType, Object value, String originalFormat, String newValue) {
            mValue = value;
            mFormatInvocationType = formatInvocationType;
            mOriginalFormat = originalFormat;
            mNewValue = newValue;
        }
    }

    public final class FormatInvocationType {
        private FormatInvocationType() {
        }

        public static final int NUMERIC = 0;
        public static final int DATE_TIME = 1;
        public static final int GENERAL = 2;
        public static final int ALL = 3;

        public static final int length = 4;
    }
}