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https://issues.apache.org/jira/browse/GROOVY-12147?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Paul King resolved GROOVY-12147.
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Fix Version/s: 6.0.0-beta-1
Resolution: Fixed
> Add locale-aware number, currency and percent formatting/parsing to the GDK
> ---------------------------------------------------------------------------
>
> Key: GROOVY-12147
> URL: https://issues.apache.org/jira/browse/GROOVY-12147
> Project: Groovy
> Issue Type: Improvement
> Components: groovy-jdk
> Reporter: Paul King
> Assignee: Paul King
> Priority: Major
> Fix For: 6.0.0-beta-1
>
>
> h2. Summary
> Groovy can already format and parse numbers, but only in a locale-invariant
> way. {{String.format(locale, ...)}} / {{sprintf}} cover locale-aware
> _grouped/decimal_ output, and {{"1234.50".toBigDecimal()}} covers _canonical_
> parsing — but there is no idiomatic way to:
> * format a number as *locale currency* ({{"€1.234,50"}}) or *locale percent*
> ({{"94,5 %"}}), or
> * parse a *locale-formatted* number, currency or percent string back to a
> {{Number}}.
> These are exactly the cases {{java.util.Formatter}} ({{%f}}, {{%%}})
> structurally cannot express (no currency conversion; {{%%}} is a literal
> sign, so no ÷100 scaling and wrong symbol placement in locales such as
> Turkish {{%94,5}} or German {{94,5 %}}). This issue adds a small set of GDK
> extension methods that wrap {{java.text.NumberFormat}} to close that gap.
> h2. Motivation
> * {{StringGroovyMethods}} conversions ({{toInteger}}, {{toDouble}},
> {{toBigDecimal}}, {{isNumber}}, …) are locale-invariant by construction
> ({{new BigDecimal(str)}} / {{Double.valueOf(str)}}) — they reject grouping
> separators, foreign decimal marks, currency symbols and percent signs.
> * {{sprintf}}/{{Formatter}} handles grouped/decimal numbers and localized
> {{%t}} dates, so no new date/time or {{sprintf}} surface is needed.
> * The only genuinely missing capability is currency/percent formatting and
> locale-aware parsing — a handful of thin {{NumberFormat}} wrappers.
> h2. Proposed API
> *Formatting* — extension methods on {{Number}} (in {{DefaultGroovyMethods}}):
> {code:java}
> public static String toCurrencyString(Number self)
> public static String toCurrencyString(Number self, Locale locale)
> public static String toPercentString(Number self)
> public static String toPercentString(Number self, Locale locale)
> {code}
> *Parsing* — extension methods on {{CharSequence}} (in
> {{StringGroovyMethods}}, alongside {{toBigDecimal}}):
> {code:java}
> public static Number toNumber(CharSequence self, Locale locale)
> public static Number toCurrencyNumber(CharSequence self)
> public static Number toCurrencyNumber(CharSequence self, Locale locale)
> public static Number toPercentNumber(CharSequence self)
> public static Number toPercentNumber(CharSequence self, Locale locale)
> {code}
> h2. Reference implementation
> {code:java}
> // --- DefaultGroovyMethods (Number) ---
> public static String toCurrencyString(Number self) {
> return NumberFormat.getCurrencyInstance().format(self);
> }
> public static String toCurrencyString(Number self, Locale locale) {
> return NumberFormat.getCurrencyInstance(locale).format(self);
> }
> public static String toPercentString(Number self) {
> return NumberFormat.getPercentInstance().format(self);
> }
> public static String toPercentString(Number self, Locale locale) {
> return NumberFormat.getPercentInstance(locale).format(self);
> }
> // --- StringGroovyMethods (CharSequence) ---
> public static Number toNumber(CharSequence self, Locale locale) {
> try {
> return NumberFormat.getNumberInstance(locale).parse(self.toString());
> } catch (ParseException e) {
> throw new NumberFormatException("Unparseable number: \"" + self +
> "\"");
> }
> }
> public static Number toCurrencyNumber(CharSequence self) {
> return toCurrencyNumber(self, Locale.getDefault());
> }
> public static Number toCurrencyNumber(CharSequence self, Locale locale) {
> NumberFormat nf = NumberFormat.getCurrencyInstance(locale);
> if (nf instanceof DecimalFormat) ((DecimalFormat)
> nf).setParseBigDecimal(true); // exact money
> try {
> return nf.parse(self.toString());
> } catch (ParseException e) {
> throw new NumberFormatException("Unparseable currency: \"" + self +
> "\"");
> }
> }
> public static Number toPercentNumber(CharSequence self) {
> return toPercentNumber(self, Locale.getDefault());
> }
> public static Number toPercentNumber(CharSequence self, Locale locale) {
> try {
> return
> NumberFormat.getPercentInstance(locale).parse(self.toString()); // unscales
> /100
> } catch (ParseException e) {
> throw new NumberFormatException("Unparseable percent: \"" + self +
> "\"");
> }
> }
> {code}
> h2. Design notes
> * *Exception convention:* {{NumberFormat.parse}} throws a checked
> {{java.text.ParseException}}; the existing conversion family throws unchecked
> {{NumberFormatException}} (e.g. {{new BigDecimal(str)}}). The parse methods
> catch and rethrow as {{NumberFormatException}} to stay consistent. No cause
> is chained, matching the current family; message style mirrors the JDK's
> {{For input string}} form without relying on the non-public
> {{NumberFormatException.forInputString}}.
> * *Money precision:* currency parsing sets {{setParseBigDecimal(true)}} so
> amounts come back as exact {{BigDecimal}} rather than lossy {{Double}}. The
> cast is {{instanceof}}-guarded because {{getCurrencyInstance}} is only
> contractually a {{NumberFormat}}.
> * *Lenient vs strict:* unlike {{toBigDecimal}} (strict, whole-string),
> {{NumberFormat.parse}} is lenient (leading numeric prefix, grouping-aware).
> This is intentional and another reason not to retrofit the existing {{toXxx}}
> methods.
> * *Naming:* {{to<Flavor><ReturnType>}} — pairs the parse side
> ({{toCurrencyNumber}}/{{toPercentNumber}}) with the format side
> ({{toCurrencyString}}/{{toPercentString}}), groups by flavor in IDE
> autocomplete, and the suffix still names the return type in the spirit of
> {{toBigDecimal}}. Bare {{toCurrency}} is avoided (reads like it returns a
> {{java.util.Currency}}).
> h2. Scope
> *In scope:* 4 formatting + 5 parsing methods (9 total), all thin
> {{java.text.NumberFormat}} wrappers.
> *Explicitly out of scope* (already covered or judged not worth the surface):
> * {{sprintf}}/{{printf}} {{Locale}} overloads on {{Object}} — would add
> methods to every metaclass; {{String.format(locale, ...)}} already covers
> grouped/decimal output.
> * {{java.time}} {{format}}/{{parse}} {{Locale}} variants — {{%t}} +
> {{String.format}} cover the common cases.
> * A locale-invariant {{parseNumber}} — redundant with
> {{toBigDecimal}}/{{toDouble}}.
> h2. Example
> {code:groovy}
> import java.util.Locale
> def de = Locale.GERMANY
> assert 1234.5.toCurrencyString(de) == '1.234,50 €'
> assert 0.945.toPercentString(de) == '94,5 %'
> assert '1.234,50 €'.toCurrencyNumber(de) == 1234.50G // BigDecimal
> assert '94,5 %'.toPercentNumber(de) == 0.945
> assert '1.234,50'.toNumber(de) == 1234.5
> {code}
> h2. Tests
> * Round-trip format→parse for representative locales (US, Germany, France,
> Turkey — Turkey to cover leading {{%}} placement).
> * Currency parse returns {{BigDecimal}}.
> * Percent parse applies ÷100 scaling.
> * Malformed input throws {{NumberFormatException}}.
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