HHH-14190 Improve efficiency of StringHelper#isBlank

hibernate-core/src/main/java/org/hibernate/internal/util/StringHelper.java

@@ -473,7 +473,20 @@ public final class StringHelper {
 	}
 
 	public static boolean isBlank(String string) {
-		return isEmpty( string ) || isEmpty( string.trim() );
+		//TODO use Java 11's more efficient String#isBlank - currently we still require Java 8 compatibility
+		if ( string == null || string.isEmpty() ) {
+			return true;
+		}
+		else {
+			//Else: we need to check all characters, preferably without using String#trim() so to
+			//not allocate temporary strings
+			for ( int i = 0; i < string.length(); i++ ) {
+				if ( ! Character.isWhitespace( string.charAt( i ) ) ) {
+					return false;
+				}
+			}
+			return true;
+		}
 	}
 
 	/**

hibernate-core/src/test/java/org/hibernate/test/util/StringHelperTest.java

@@ -18,6 +18,7 @@ import org.hibernate.internal.util.StringHelper;
 import org.hibernate.testing.junit4.BaseUnitTestCase;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertTrue;
 
@@ -44,6 +45,18 @@ public class StringHelperTest extends BaseUnitTestCase {
 		assertEquals( "internal.util.StringHelper", StringHelper.partiallyUnqualify( STRING_HELPER_FQN, BASE_PACKAGE ) );
 	}
 
+	@Test
+	public void testIsBlank() {
+		assertFalse( StringHelper.isBlank( "A" ) );
+		assertFalse( StringHelper.isBlank( " a" ) );
+		assertFalse( StringHelper.isBlank( "a " ) );
+		assertFalse( StringHelper.isBlank( "a\t" ) );
+		assertTrue( StringHelper.isBlank( "\t\n" ) );
+		assertTrue( StringHelper.isBlank( null ) );
+		assertTrue( StringHelper.isBlank( "" ) );
+		assertTrue( StringHelper.isBlank( "     " ) );
+	}
+
 	@Test
 	public void testBasePackageCollapsing() {
 		assertNull( StringHelper.collapseQualifierBase( null, BASE_PACKAGE ) );