Document options for Date/Time parsing & formatting issues with JDK 20+

This commit updates Javadoc and the reference guide to document options
for handling date/time parsing and formatting issues on JDK 20 and higher.

A new "Date and Time Formatting with JDK 20 and higher" page has also been
introduced in the wiki.

https://github.com/spring-projects/spring-framework/wiki/Date-and-Time-Formatting-with-JDK-20-and-higher

Closes gh-33151

framework-docs/modules/ROOT/pages/core/validation/format.adoc

@@ -280,10 +280,11 @@ Kotlin::
 
 A portable format annotation API exists in the `org.springframework.format.annotation`
 package. You can use `@NumberFormat` to format `Number` fields such as `Double` and
-`Long`, and `@DateTimeFormat` to format `java.util.Date`, `java.util.Calendar`, `Long`
+`Long`, and `@DateTimeFormat` to format fields such as `java.util.Date`,
-(for millisecond timestamps) as well as JSR-310 `java.time`.
+`java.util.Calendar`, and `Long` (for millisecond timestamps) as well as JSR-310
+`java.time` types.
 
-The following example uses `@DateTimeFormat` to format a `java.util.Date` as an ISO Date
+The following example uses `@DateTimeFormat` to format a `java.util.Date` as an ISO date
 (yyyy-MM-dd):
 
 [tabs]
@@ -309,6 +310,28 @@ Kotlin::
 ----
 ======
 
+For further details, see the javadoc for
+{spring-framework-api}/format/annotation/DateTimeFormat.html[`@DateTimeFormat`] and
+{spring-framework-api}/format/annotation/NumberFormat.html[`@NumberFormat`].
+
+[WARNING]
+====
+Style-based formatting and parsing rely on locale-sensitive patterns which may change
+depending on the Java runtime. Specifically, applications that rely on date, time, or
+number parsing and formatting may encounter incompatible changes in behavior when running
+on JDK 20 or higher.
+
+Using an ISO standardized format or a concrete pattern that you control allows for
+reliable system-independent and locale-independent parsing and formatting of date, time,
+and number values.
+
+For `@DateTimeFormat`, the use of fallback patterns can also help to address
+compatibility issues.
+
+For further details, see the
+https://github.com/spring-projects/spring-framework/wiki/Date-and-Time-Formatting-with-JDK-20-and-higher[Date and Time Formatting with JDK 20 and higher]
+page in the Spring Framework wiki.
+====
 
 [[format-FormatterRegistry-SPI]]
 == The `FormatterRegistry` SPI

framework-docs/modules/ROOT/pages/web/webflux/config.adoc

@@ -91,7 +91,7 @@ class WebConfig : WebFluxConfigurer {
 [.small]#xref:web/webmvc/mvc-config/conversion.adoc[See equivalent in the Servlet stack]#
 
 By default, formatters for various number and date types are installed, along with support
-for customization via `@NumberFormat` and `@DateTimeFormat` on fields.
+for customization via `@NumberFormat` and `@DateTimeFormat` on fields and parameters.
 
 To register custom formatters and converters in Java config, use the following:
 

framework-docs/modules/ROOT/pages/web/webmvc/mvc-config/conversion.adoc

@@ -4,7 +4,7 @@
 [.small]#xref:web/webflux/config.adoc#webflux-config-conversion[See equivalent in the Reactive stack]#
 
 By default, formatters for various number and date types are installed, along with support
-for customization via `@NumberFormat` and `@DateTimeFormat` on fields.
+for customization via `@NumberFormat` and `@DateTimeFormat` on fields and parameters.
 
 To register custom formatters and converters in Java config, use the following:
 

spring-context/src/main/java/org/springframework/format/annotation/DateTimeFormat.java

@@ -28,17 +28,27 @@ import java.lang.annotation.Target;
  * <p>Formatting applies to parsing a date/time object from a string as well as printing a
  * date/time object to a string.
  *
- * <p>Supports formatting by style pattern, ISO date time pattern, or custom format pattern string.
+ * <p>Supports formatting by style pattern, ISO date/time pattern, or custom format pattern string.
  * Can be applied to {@link java.util.Date}, {@link java.util.Calendar}, {@link Long} (for
  * millisecond timestamps) as well as JSR-310 {@code java.time} value types.
  *
  * <p>For style-based formatting, set the {@link #style} attribute to the desired style pattern code.
  * The first character of the code is the date style, and the second character is the time style.
  * Specify a character of 'S' for short style, 'M' for medium, 'L' for long, and 'F' for full.
- * The date or time may be omitted by specifying the style character '-' &mdash; for example,
+ * The date or time may be omitted by specifying the style character '-'. For example,
  * 'M-' specifies a medium format for the date with no time. The supported style pattern codes
  * correlate to the enum constants defined in {@link java.time.format.FormatStyle}.
  *
+ * <p><strong>WARNING</strong>: Style-based formatting and parsing rely on locale-sensitive
+ * patterns which may change depending on the Java runtime. Specifically, applications that
+ * rely on date/time parsing and formatting may encounter incompatible changes in behavior
+ * when running on JDK 20 or higher. Using an ISO standardized format or a concrete pattern
+ * that you control allows for reliable system-independent and locale-independent parsing and
+ * formatting of date/time values. The use of {@linkplain #fallbackPatterns() fallback patterns}
+ * can also help to address compatibility issues. For further details, see the
+ * <a href="https://github.com/spring-projects/spring-framework/wiki/Date-and-Time-Formatting-with-JDK-20-and-higher">
+ * Date and Time Formatting with JDK 20 and higher</a> page in the Spring Framework wiki.
+ *
  * <p>For ISO-based formatting, set the {@link #iso} attribute to the desired {@link ISO} format,
  * such as {@link ISO#DATE}.
  *