Use ResolverStyle.SMART when a custom format is specified

Fixes gh-13970

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/format/WebConversionService.java

@@ -89,7 +89,7 @@ public class WebConversionService extends DefaultFormattingConversionService {
 		DateTimeFormatterRegistrar dateTime = new DateTimeFormatterRegistrar();
 		if (this.dateFormat != null) {
 			dateTime.setDateFormatter(DateTimeFormatter.ofPattern(this.dateFormat)
-					.withResolverStyle(ResolverStyle.STRICT));
+					.withResolverStyle(ResolverStyle.SMART));
 		}
 		dateTime.registerFormatters(this);
 	}

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/format/WebConversionServiceTests.java

@@ -28,6 +28,7 @@ import static org.assertj.core.api.Assertions.assertThat;
  * Tests for {@link WebConversionService}.
  *
  * @author Brian Clozel
+ * @author Madhura Bhave
  */
 public class WebConversionServiceTests {
 
@@ -44,4 +45,12 @@ public class WebConversionServiceTests {
 				.isEqualTo("01*01*2018");
 	}
 
+	@Test
+	public void convertFromStringToDate() {
+		WebConversionService conversionService = new WebConversionService("yyyy-MM-dd");
+		java.time.LocalDate date = conversionService.convert("2018-01-01",
+				java.time.LocalDate.class);
+		assertThat(date).isEqualTo(java.time.LocalDate.of(2018, 1, 1));
+	}
+
 }