JodaTimeFormatterRegistrar defensively checks whether Joda-Time 2.x is present (for Joda-Time 1.x tolerance on the classpath)

Also switches 4.2.4's new formatter implementations to package visibility, just in case they'll be superseded by another variant in the future.

Issue: SPR-13730

spring-context/src/main/java/org/springframework/format/datetime/joda/DurationFormatter.java

@@ -31,7 +31,7 @@ import org.springframework.format.Formatter;
  * @since 4.2.4
  * @see Duration#parse
  */
-public class DurationFormatter implements Formatter<Duration> {
+class DurationFormatter implements Formatter<Duration> {
 
 	@Override
 	public Duration parse(String text, Locale locale) throws ParseException {

spring-context/src/main/java/org/springframework/format/datetime/joda/JodaTimeFormatterRegistrar.java

@@ -38,6 +38,7 @@ import org.springframework.format.FormatterRegistry;
 import org.springframework.format.Parser;
 import org.springframework.format.Printer;
 import org.springframework.format.annotation.DateTimeFormat.ISO;
+import org.springframework.util.ClassUtils;
 
 /**
  * Configures Joda-Time's formatting system for use with Spring.
@@ -61,6 +62,14 @@ public class JodaTimeFormatterRegistrar implements FormatterRegistrar {
 	private enum Type {DATE, TIME, DATE_TIME}
 
 
+	/**
+	 * Strictly speaking, this should not be necessary since we formally require JodaTime 2.x.
+	 * However, since Joda-Time formatters are being registered automatically, we defensively
+	 * adapt to Joda-Time 1.x when encountered on the classpath. To be removed in Spring 5.0.
+	 */
+	private static final boolean jodaTime2Available = ClassUtils.isPresent(
+			"org.joda.time.YearMonth", JodaTimeFormatterRegistrar.class.getClassLoader());
+
 	/**
 	 * User defined formatters.
 	 */
@@ -200,8 +209,9 @@ public class JodaTimeFormatterRegistrar implements FormatterRegistrar {
 
 		registry.addFormatterForFieldType(Period.class, new PeriodFormatter());
 		registry.addFormatterForFieldType(Duration.class, new DurationFormatter());
-		registry.addFormatterForFieldType(YearMonth.class, new YearMonthFormatter());
-		registry.addFormatterForFieldType(MonthDay.class, new MonthDayFormatter());
+		if (jodaTime2Available) {
+			JodaTime2Delegate.registerAdditionalFormatters(registry);
+		}
 
 		registry.addFormatterForFieldAnnotation(new JodaDateTimeFormatAnnotationFormatterFactory());
 	}
@@ -231,4 +241,16 @@ public class JodaTimeFormatterRegistrar implements FormatterRegistrar {
 		}
 	}
 
+
+	/**
+	 * Inner class to avoid a hard dependency on Joda-Time 2.x.
+	 */
+	private static class JodaTime2Delegate {
+
+		public static void registerAdditionalFormatters(FormatterRegistry registry) {
+			registry.addFormatterForFieldType(YearMonth.class, new YearMonthFormatter());
+			registry.addFormatterForFieldType(MonthDay.class, new MonthDayFormatter());
+		}
+	}
+
 }

spring-context/src/main/java/org/springframework/format/datetime/joda/MonthDayFormatter.java

@@ -31,7 +31,7 @@ import org.springframework.format.Formatter;
  * @since 4.2.4
  * @see MonthDay#parse
  */
-public class MonthDayFormatter implements Formatter<MonthDay> {
+class MonthDayFormatter implements Formatter<MonthDay> {
 
 	@Override
 	public MonthDay parse(String text, Locale locale) throws ParseException {

spring-context/src/main/java/org/springframework/format/datetime/joda/PeriodFormatter.java

@@ -31,7 +31,7 @@ import org.springframework.format.Formatter;
  * @since 4.2.4
  * @see Period#parse
  */
-public class PeriodFormatter implements Formatter<Period> {
+class PeriodFormatter implements Formatter<Period> {
 
 	@Override
 	public Period parse(String text, Locale locale) throws ParseException {

spring-context/src/main/java/org/springframework/format/datetime/joda/YearMonthFormatter.java

@@ -31,7 +31,7 @@ import org.springframework.format.Formatter;
  * @since 4.2.4
  * @see YearMonth#parse
  */
-public class YearMonthFormatter implements Formatter<YearMonth> {
+class YearMonthFormatter implements Formatter<YearMonth> {
 
 	@Override
 	public YearMonth parse(String text, Locale locale) throws ParseException {

spring-context/src/main/java/org/springframework/format/datetime/standard/DurationFormatter.java

@@ -32,7 +32,7 @@ import org.springframework.lang.UsesJava8;
  * @see Duration#parse
  */
 @UsesJava8
-public class DurationFormatter implements Formatter<Duration> {
+class DurationFormatter implements Formatter<Duration> {
 
 	@Override
 	public Duration parse(String text, Locale locale) throws ParseException {

spring-context/src/main/java/org/springframework/format/datetime/standard/MonthDayFormatter.java

@@ -32,7 +32,7 @@ import org.springframework.lang.UsesJava8;
  * @see MonthDay#parse
  */
 @UsesJava8
-public class MonthDayFormatter implements Formatter<MonthDay> {
+class MonthDayFormatter implements Formatter<MonthDay> {
 
 	@Override
 	public MonthDay parse(String text, Locale locale) throws ParseException {

spring-context/src/main/java/org/springframework/format/datetime/standard/PeriodFormatter.java

@@ -33,7 +33,7 @@ import org.springframework.lang.UsesJava8;
  * @see Period#parse
  */
 @UsesJava8
-public class PeriodFormatter implements Formatter<Period> {
+class PeriodFormatter implements Formatter<Period> {
 
 	@Override
 	public Period parse(String text, Locale locale) throws ParseException {

spring-context/src/main/java/org/springframework/format/datetime/standard/YearMonthFormatter.java

@@ -32,7 +32,7 @@ import org.springframework.lang.UsesJava8;
  * @see YearMonth#parse
  */
 @UsesJava8
-public class YearMonthFormatter implements Formatter<YearMonth> {
+class YearMonthFormatter implements Formatter<YearMonth> {
 
 	@Override
 	public YearMonth parse(String text, Locale locale) throws ParseException {