Polish "Add support for converting String to Pattern"

See gh-24311

spring-core/src/main/java/org/springframework/core/convert/support/DefaultConversionService.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -22,6 +22,7 @@ import java.util.Locale;
 import java.util.UUID;
 import java.util.regex.Pattern;
 
+import org.springframework.core.KotlinDetector;
 import org.springframework.core.convert.ConversionService;
 import org.springframework.core.convert.converter.ConverterRegistry;
 import org.springframework.lang.Nullable;
@@ -170,6 +171,11 @@ public class DefaultConversionService extends GenericConversionService {
 
 		converterRegistry.addConverter(new StringToPatternConverter());
 		converterRegistry.addConverter(Pattern.class, String.class, new ObjectToStringConverter());
+
+		if (KotlinDetector.isKotlinPresent()) {
+			converterRegistry.addConverter(new StringToRegexConverter());
+			converterRegistry.addConverter(kotlin.text.Regex.class, String.class, new ObjectToStringConverter());
+		}
 	}
 
 }

spring-core/src/main/java/org/springframework/core/convert/support/StringToPatternConverter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -21,15 +21,19 @@ import java.util.regex.Pattern;
 import org.springframework.core.convert.converter.Converter;
 
 /**
- * Convert a String to a {@link Pattern}.
+ * Converts from a String to a {@link java.util.regex.Pattern}.
  *
  * @author Valery Yatsynovich
- * @since 5.2
+ * @author Stephane Nicoll
+ * @since 6.1
  */
-class StringToPatternConverter implements Converter<String, Pattern> {
+final class StringToPatternConverter implements Converter<String, Pattern> {
 
 	@Override
 	public Pattern convert(String source) {
+		if (source.isEmpty()) {
+			return null;
+		}
 		return Pattern.compile(source);
 	}
 

spring-core/src/main/kotlin/org/springframework/core/convert/support/StringToRegexConverter.kt

@@ -0,0 +1,19 @@
+package org.springframework.core.convert.support
+
+import org.springframework.core.convert.converter.Converter
+
+/**
+ * Converts from a String to a [Regex].
+ *
+ * @author Stephane Nicoll
+ */
+class StringToRegexConverter : Converter<String, Regex> {
+
+	override fun convert(source: String): Regex? {
+		if (source.isEmpty()) {
+			return null
+		}
+		return source.toRegex()
+	}
+
+}