StringUtils:

- use new StringUtils.split(..., boolean trim, boolean excludeEmpty) where possible
- added substringTrimmed() and isTrimmedEmpty() to avoid temporary string  allocation

flatlaf-core/src/main/java/com/formdev/flatlaf/UIDefaultsLoader.java

@@ -392,7 +392,7 @@ class UIDefaultsLoader
 			//     Syntax: lazy(uiKey)
 			if( value.startsWith( "lazy(" ) && value.endsWith( ")" ) ) {
 				resultValueType[0] = ValueType.LAZY;
-				String uiKey = value.substring( 5, value.length() - 1 ).trim();
+				String uiKey = StringUtils.substringTrimmed( value, 5, value.length() - 1 );
 				return (LazyValue) t -> {
 					return lazyUIManagerGet( uiKey );
 				};
@@ -514,7 +514,7 @@ class UIDefaultsLoader
 	private static Object parseBorder( String value, Function<String, String> resolver, List<ClassLoader> addonClassLoaders ) {
 		if( value.indexOf( ',' ) >= 0 ) {
 			// top,left,bottom,right[,lineColor[,lineThickness]]
-			List<String> parts = split( value, ',' );
+			List<String> parts = StringUtils.split( value, ',', true, false );
 			Insets insets = parseInsets( value );
 			ColorUIResource lineColor = (parts.size() >= 5)
 				? (ColorUIResource) parseColorOrFunction( resolver.apply( parts.get( 4 ) ), resolver, true )
@@ -571,7 +571,7 @@ class UIDefaultsLoader
 	}
 
 	private static Insets parseInsets( String value ) {
-		List<String> numbers = split( value, ',' );
+		List<String> numbers = StringUtils.split( value, ',', true, false );
 		try {
 			return new InsetsUIResource(
 				Integer.parseInt( numbers.get( 0 ) ),
@@ -584,7 +584,7 @@ class UIDefaultsLoader
 	}
 
 	private static Dimension parseDimension( String value ) {
-		List<String> numbers = split( value, ',' );
+		List<String> numbers = StringUtils.split( value, ',', true, false );
 		try {
 			return new DimensionUIResource(
 				Integer.parseInt( numbers.get( 0 ) ),
@@ -672,7 +672,7 @@ class UIDefaultsLoader
 			return null;
 		}
 
-		String function = value.substring( 0, paramsStart ).trim();
+		String function = StringUtils.substringTrimmed( value, 0, paramsStart );
 		List<String> params = splitFunctionParams( value.substring( paramsStart + 1, value.length() - 1 ), ',' );
 		if( params.isEmpty() )
 			throwMissingParametersException( value );
@@ -1075,7 +1075,7 @@ class UIDefaultsLoader
 	}
 
 	private static Object parseGrayFilter( String value ) {
-		List<String> numbers = split( value, ',' );
+		List<String> numbers = StringUtils.split( value, ',', true, false );
 		try {
 			int brightness = Integer.parseInt( numbers.get( 0 ) );
 			int contrast = Integer.parseInt( numbers.get( 1 ) );
@@ -1089,20 +1089,6 @@ class UIDefaultsLoader
 		}
 	}
 
-	/**
-	 * Split string and trim parts.
-	 */
-	private static List<String> split( String str, char delim ) {
-		List<String> result = StringUtils.split( str, delim );
-
-		// trim strings
-		int size = result.size();
-		for( int i = 0; i < size; i++ )
-			result.set( i, result.get( i ).trim() );
-
-		return result;
-	}
-
 	/**
 	 * Splits function parameters and allows using functions as parameters.
 	 * In other words: Delimiters surrounded by '(' and ')' are ignored.
@@ -1119,11 +1105,11 @@ class UIDefaultsLoader
 			else if( ch == ')' )
 				nestLevel--;
 			else if( nestLevel == 0 && ch == delim ) {
-				strs.add( str.substring( start, i ).trim() );
+				strs.add( StringUtils.substringTrimmed( str, start, i ) );
 				start = i + 1;
 			}
 		}
-		strs.add( str.substring( start ).trim() );
+		strs.add( StringUtils.substringTrimmed( str, start ) );
 
 		return strs;
 	}

flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatStylingSupport.java

@@ -252,7 +252,7 @@ public class FlatStylingSupport
 		if( style instanceof String ) {
 			// handle style in CSS syntax
 			String str = (String) style;
-			if( str.trim().isEmpty() )
+			if( StringUtils.isTrimmedEmpty( str ) )
 				return null;
 
 			return applyStyle( parse( str ), applyProperty );
@@ -307,26 +307,21 @@ public class FlatStylingSupport
 	public static Map<String, Object> parse( String style )
 		throws IllegalArgumentException
 	{
-		if( style == null || style.trim().isEmpty() )
+		if( style == null || StringUtils.isTrimmedEmpty( style ) )
 			return null;
 
 		Map<String, Object> map = null;
 
 		// split style into parts and process them
-		for( String part : StringUtils.split( style, ';' ) ) {
+		for( String part : StringUtils.split( style, ';', true, true ) ) {
-			// ignore empty parts
-			part = part.trim();
-			if( part.isEmpty() )
-				continue;
-
 			// find separator colon
 			int sepIndex = part.indexOf( ':' );
 			if( sepIndex < 0 )
 				throw new IllegalArgumentException( "missing colon in '" + part + "'" );
 
 			// split into key and value
-			String key = part.substring( 0, sepIndex ).trim();
+			String key = StringUtils.substringTrimmed( part, 0, sepIndex );
-			String value = part.substring( sepIndex + 1 ).trim();
+			String value = StringUtils.substringTrimmed( part, sepIndex + 1 );
 			if( key.isEmpty() )
 				throw new IllegalArgumentException( "missing key in '" + part + "'" );
 			if( value.isEmpty() )

flatlaf-core/src/main/java/com/formdev/flatlaf/util/StringUtils.java

@@ -79,18 +79,66 @@ public class StringUtils
 		return strs;
 	}
 
-	private static void add( List<String> strs, String str, int begin, int end, boolean trim, boolean excludeEmpty ) {
+	private static void add( List<String> strs, String str, int beginIndex, int endIndex,
+		boolean trim, boolean excludeEmpty )
+	{
 		if( trim ) {
-			// skip leading whitespace
+			beginIndex = trimBegin( str, beginIndex, endIndex );
-			while( begin < end && str.charAt( begin ) <= ' ' )
+			endIndex = trimEnd( str, beginIndex, endIndex );
-				begin++;
-
-			// skip trailing whitespace
-			while( begin < end && str.charAt( end - 1 ) <= ' ' )
-				end--;
 		}
 
-		if( !excludeEmpty || end > begin )
+		if( !excludeEmpty || endIndex > beginIndex )
-			strs.add( str.substring( begin, end ) );
+			strs.add( str.substring( beginIndex, endIndex ) );
+	}
+
+	/**
+	 * This is equal to {@code str.substring( beginIndex, endIndex ).trim()},
+	 * but avoids temporary untrimmed substring allocation.
+	 * If the trimmed string is empty, a shared empty string is returned.
+	 *
+	 * @since 2
+	 */
+	public static String substringTrimmed( String str, int beginIndex ) {
+		return substringTrimmed( str, beginIndex, str.length() );
+	}
+
+	/**
+	 * This is equal to {@code str.substring( beginIndex ).trim()},
+	 * but avoids temporary untrimmed substring allocation.
+	 * If the trimmed string is empty, a shared empty string is returned.
+	 *
+	 * @since 2
+	 */
+	public static String substringTrimmed( String str, int beginIndex, int endIndex ) {
+		beginIndex = trimBegin( str, beginIndex, endIndex );
+		endIndex = trimEnd( str, beginIndex, endIndex );
+		return (endIndex > beginIndex) ? str.substring( beginIndex, endIndex ) : "";
+	}
+
+	/**
+	 * This is equal to {@code str.trim().isEmpty()},
+	 * but avoids temporary trimmed substring allocation.
+	 *
+	 * @since 2
+	 */
+	public static boolean isTrimmedEmpty( String str ) {
+		int length = str.length();
+		int beginIndex = trimBegin( str, 0, length );
+		int endIndex = trimEnd( str, beginIndex, length );
+		return beginIndex >= endIndex;
+	}
+
+	private static int trimBegin( String str, int beginIndex, int endIndex ) {
+		// skip leading whitespace
+		while( beginIndex < endIndex && str.charAt( beginIndex ) <= ' ' )
+			beginIndex++;
+		return beginIndex;
+	}
+
+	private static int trimEnd( String str, int beginIndex, int endIndex ) {
+		// skip trailing whitespace
+		while( beginIndex < endIndex && str.charAt( endIndex - 1 ) <= ' ' )
+			endIndex--;
+		return endIndex;
 	}
 }

flatlaf-core/src/test/java/com/formdev/flatlaf/util/TestStringUtils.java

@@ -195,4 +195,46 @@ public class TestStringUtils
 			Arrays.asList( "a", "b", "c" ),
 			StringUtils.split( "a\n\n\nb\n\nc", '\n', true, true ) );
 	}
+
+	@Test
+	void substringTrimmed() {
+		testSubstringTrimmed( "", 0 );
+
+		testSubstringTrimmed( "a", 0 );
+		testSubstringTrimmed( "a", 1 );
+
+		testSubstringTrimmed( "a  ", 0 );
+		testSubstringTrimmed( "  a", 0 );
+		testSubstringTrimmed( "  a  ", 0 );
+
+		testSubstringTrimmed( "  a  ", 1 );
+
+		testSubstringTrimmed( "  a  ", 0, 3 );
+		testSubstringTrimmed( "  a  ", 1, 4 );
+	}
+
+	private void testSubstringTrimmed( String str, int beginIndex ) {
+		assertEquals(
+			str.substring( beginIndex ).trim(),
+			StringUtils.substringTrimmed( str, beginIndex ) );
+	}
+
+	private void testSubstringTrimmed( String str, int beginIndex, int endIndex ) {
+		assertEquals(
+			str.substring( beginIndex, endIndex ).trim(),
+			StringUtils.substringTrimmed( str, beginIndex, endIndex ) );
+	}
+
+	@Test
+	void trimmedEmpty() {
+		testTrimmedEmpty( "" );
+		testTrimmedEmpty( "a" );
+		testTrimmedEmpty( " a " );
+		testTrimmedEmpty( " " );
+		testTrimmedEmpty( "  " );
+	}
+
+	private void testTrimmedEmpty( String str ) {
+		assertEquals( str.trim().isEmpty(), StringUtils.isTrimmedEmpty( str ) );
+	}
 }