Default fallback parsing for UTC without milliseconds

Closes gh-32856

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -22,8 +22,10 @@ import java.text.SimpleDateFormat;
 import java.util.Collections;
 import java.util.Date;
 import java.util.EnumMap;
+import java.util.LinkedHashSet;
 import java.util.Locale;
 import java.util.Map;
+import java.util.Set;
 import java.util.TimeZone;
 
 import org.springframework.format.Formatter;
@@ -35,9 +37,14 @@ import org.springframework.util.StringUtils;
 
 /**
  * A formatter for {@link java.util.Date} types.
+ *
  * <p>Supports the configuration of an explicit date time pattern, timezone,
  * locale, and fallback date time patterns for lenient parsing.
  *
+ * <p>Common ISO patterns for UTC instants are applied at millisecond precision.
+ * Note that {@link org.springframework.format.datetime.standard.InstantFormatter}
+ * is recommended for flexible UTC parsing into a {@link java.time.Instant} instead.
+ *
  * @author Keith Donald
  * @author Juergen Hoeller
  * @author Phillip Webb
@@ -49,15 +56,23 @@ public class DateFormatter implements Formatter<Date> {
 
 	private static final TimeZone UTC = TimeZone.getTimeZone("UTC");
 
-	// We use an EnumMap instead of Map.of(...) since the former provides better performance.
 	private static final Map<ISO, String> ISO_PATTERNS;
 
+	private static final Map<ISO, String> ISO_FALLBACK_PATTERNS;
+
 	static {
+		// We use an EnumMap instead of Map.of(...) since the former provides better performance.
 		Map<ISO, String> formats = new EnumMap<>(ISO.class);
 		formats.put(ISO.DATE, "yyyy-MM-dd");
 		formats.put(ISO.TIME, "HH:mm:ss.SSSXXX");
 		formats.put(ISO.DATE_TIME, "yyyy-MM-dd'T'HH:mm:ss.SSSXXX");
 		ISO_PATTERNS = Collections.unmodifiableMap(formats);
+
+		// Fallback format for the time part without milliseconds.
+		Map<ISO, String> fallbackFormats = new EnumMap<>(ISO.class);
+		fallbackFormats.put(ISO.TIME, "HH:mm:ssXXX");
+		fallbackFormats.put(ISO.DATE_TIME, "yyyy-MM-dd'T'HH:mm:ssXXX");
+		ISO_FALLBACK_PATTERNS = Collections.unmodifiableMap(fallbackFormats);
 	}
 
 
@@ -202,8 +217,16 @@ public class DateFormatter implements Formatter<Date> {
 			return getDateFormat(locale).parse(text);
 		}
 		catch (ParseException ex) {
+			Set<String> fallbackPatterns = new LinkedHashSet<>();
+			String isoPattern = ISO_FALLBACK_PATTERNS.get(this.iso);
+			if (isoPattern != null) {
+				fallbackPatterns.add(isoPattern);
+			}
 			if (!ObjectUtils.isEmpty(this.fallbackPatterns)) {
-				for (String pattern : this.fallbackPatterns) {
+				Collections.addAll(fallbackPatterns, this.fallbackPatterns);
+			}
+			if (!fallbackPatterns.isEmpty()) {
+				for (String pattern : fallbackPatterns) {
 					try {
 						DateFormat dateFormat = configureDateFormat(new SimpleDateFormat(pattern, locale));
 						// Align timezone for parsing format with printing format if ISO is set.

spring-context/src/test/java/org/springframework/format/datetime/DateFormatterTests.java

@@ -35,6 +35,7 @@ import static org.assertj.core.api.Assertions.assertThatIllegalStateException;
  *
  * @author Keith Donald
  * @author Phillip Webb
+ * @author Juergen Hoeller
  */
 class DateFormatterTests {
 
@@ -45,6 +46,7 @@ class DateFormatterTests {
 	void shouldPrintAndParseDefault() throws Exception {
 		DateFormatter formatter = new DateFormatter();
 		formatter.setTimeZone(UTC);
+
 		Date date = getDate(2009, Calendar.JUNE, 1);
 		assertThat(formatter.print(date, Locale.US)).isEqualTo("Jun 1, 2009");
 		assertThat(formatter.parse("Jun 1, 2009", Locale.US)).isEqualTo(date);
@@ -54,6 +56,7 @@ class DateFormatterTests {
 	void shouldPrintAndParseFromPattern() throws ParseException {
 		DateFormatter formatter = new DateFormatter("yyyy-MM-dd");
 		formatter.setTimeZone(UTC);
+
 		Date date = getDate(2009, Calendar.JUNE, 1);
 		assertThat(formatter.print(date, Locale.US)).isEqualTo("2009-06-01");
 		assertThat(formatter.parse("2009-06-01", Locale.US)).isEqualTo(date);
@@ -64,6 +67,7 @@ class DateFormatterTests {
 		DateFormatter formatter = new DateFormatter();
 		formatter.setTimeZone(UTC);
 		formatter.setStyle(DateFormat.SHORT);
+
 		Date date = getDate(2009, Calendar.JUNE, 1);
 		assertThat(formatter.print(date, Locale.US)).isEqualTo("6/1/09");
 		assertThat(formatter.parse("6/1/09", Locale.US)).isEqualTo(date);
@@ -74,6 +78,7 @@ class DateFormatterTests {
 		DateFormatter formatter = new DateFormatter();
 		formatter.setTimeZone(UTC);
 		formatter.setStyle(DateFormat.MEDIUM);
+
 		Date date = getDate(2009, Calendar.JUNE, 1);
 		assertThat(formatter.print(date, Locale.US)).isEqualTo("Jun 1, 2009");
 		assertThat(formatter.parse("Jun 1, 2009", Locale.US)).isEqualTo(date);
@@ -84,6 +89,7 @@ class DateFormatterTests {
 		DateFormatter formatter = new DateFormatter();
 		formatter.setTimeZone(UTC);
 		formatter.setStyle(DateFormat.LONG);
+
 		Date date = getDate(2009, Calendar.JUNE, 1);
 		assertThat(formatter.print(date, Locale.US)).isEqualTo("June 1, 2009");
 		assertThat(formatter.parse("June 1, 2009", Locale.US)).isEqualTo(date);
@@ -94,16 +100,18 @@ class DateFormatterTests {
 		DateFormatter formatter = new DateFormatter();
 		formatter.setTimeZone(UTC);
 		formatter.setStyle(DateFormat.FULL);
+
 		Date date = getDate(2009, Calendar.JUNE, 1);
 		assertThat(formatter.print(date, Locale.US)).isEqualTo("Monday, June 1, 2009");
 		assertThat(formatter.parse("Monday, June 1, 2009", Locale.US)).isEqualTo(date);
 	}
 
 	@Test
-	void shouldPrintAndParseISODate() throws Exception {
+	void shouldPrintAndParseIsoDate() throws Exception {
 		DateFormatter formatter = new DateFormatter();
 		formatter.setTimeZone(UTC);
 		formatter.setIso(ISO.DATE);
+
 		Date date = getDate(2009, Calendar.JUNE, 1, 14, 23, 5, 3);
 		assertThat(formatter.print(date, Locale.US)).isEqualTo("2009-06-01");
 		assertThat(formatter.parse("2009-6-01", Locale.US))
@@ -111,32 +119,43 @@ class DateFormatterTests {
 	}
 
 	@Test
-	void shouldPrintAndParseISOTime() throws Exception {
+	void shouldPrintAndParseIsoTime() throws Exception {
 		DateFormatter formatter = new DateFormatter();
 		formatter.setTimeZone(UTC);
 		formatter.setIso(ISO.TIME);
+
 		Date date = getDate(2009, Calendar.JANUARY, 1, 14, 23, 5, 3);
 		assertThat(formatter.print(date, Locale.US)).isEqualTo("14:23:05.003Z");
 		assertThat(formatter.parse("14:23:05.003Z", Locale.US))
 				.isEqualTo(getDate(1970, Calendar.JANUARY, 1, 14, 23, 5, 3));
+
+		date = getDate(2009, Calendar.JANUARY, 1, 14, 23, 5, 0);
+		assertThat(formatter.print(date, Locale.US)).isEqualTo("14:23:05.000Z");
+		assertThat(formatter.parse("14:23:05Z", Locale.US))
+				.isEqualTo(getDate(1970, Calendar.JANUARY, 1, 14, 23, 5, 0).toInstant());
 	}
 
 	@Test
-	void shouldPrintAndParseISODateTime() throws Exception {
+	void shouldPrintAndParseIsoDateTime() throws Exception {
 		DateFormatter formatter = new DateFormatter();
 		formatter.setTimeZone(UTC);
 		formatter.setIso(ISO.DATE_TIME);
+
 		Date date = getDate(2009, Calendar.JUNE, 1, 14, 23, 5, 3);
 		assertThat(formatter.print(date, Locale.US)).isEqualTo("2009-06-01T14:23:05.003Z");
 		assertThat(formatter.parse("2009-06-01T14:23:05.003Z", Locale.US)).isEqualTo(date);
+
+		date = getDate(2009, Calendar.JUNE, 1, 14, 23, 5, 0);
+		assertThat(formatter.print(date, Locale.US)).isEqualTo("2009-06-01T14:23:05.000Z");
+		assertThat(formatter.parse("2009-06-01T14:23:05Z", Locale.US)).isEqualTo(date.toInstant());
 	}
 
 	@Test
 	void shouldThrowOnUnsupportedStylePattern() {
 		DateFormatter formatter = new DateFormatter();
 		formatter.setStylePattern("OO");
-		assertThatIllegalStateException().isThrownBy(() ->
+
-				formatter.parse("2009", Locale.US))
+		assertThatIllegalStateException().isThrownBy(() -> formatter.parse("2009", Locale.US))
 				.withMessageContaining("Unsupported style pattern 'OO'");
 	}
 
@@ -148,8 +167,8 @@ class DateFormatterTests {
 		formatter.setStylePattern("L-");
 		formatter.setIso(ISO.DATE_TIME);
 		formatter.setPattern("yyyy");
-		Date date = getDate(2009, Calendar.JUNE, 1, 14, 23, 5, 3);
 
+		Date date = getDate(2009, Calendar.JUNE, 1, 14, 23, 5, 3);
 		assertThat(formatter.print(date, Locale.US)).as("uses pattern").isEqualTo("2009");
 
 		formatter.setPattern("");