Support letters other than A-Z in identifiers in SpEL

Prior to this commit, only the letters 'A' - 'Z' (ignoring case) were
supported in identifiers (i.e., property, field, and variable names).

This known (yet undocumented) limitation prevented the use of characters
such as 'ü', 'ñ', 'é' as well as letters from other character sets such
as Chinese, Japanese, Cyrillic, etc.

This commit lifts that restriction by delegating to Character.isLetter()
to determine if a character in a SpEL expression is a letter.

Closes gh-30580

Author: sbrannen

spring-expression/src/main/java/org/springframework/expression/spel/standard/Tokenizer.java

@@ -30,6 +30,7 @@
  * @author Andy Clement
  * @author Juergen Hoeller
  * @author Phillip Webb
+ * @author Sam Brannen
  * @since 3.0
  */
 class Tokenizer {
@@ -44,8 +45,6 @@ class Tokenizer {
 
 	private static final byte IS_HEXDIGIT = 0x02;
 
-	private static final byte IS_ALPHA = 0x04;
-
 	static {
 		for (int ch = '0'; ch <= '9'; ch++) {
 			FLAGS[ch] |= IS_DIGIT | IS_HEXDIGIT;
@@ -56,12 +55,6 @@ class Tokenizer {
 		for (int ch = 'a'; ch <= 'f'; ch++) {
 			FLAGS[ch] |= IS_HEXDIGIT;
 		}
-		for (int ch = 'A'; ch <= 'Z'; ch++) {
-			FLAGS[ch] |= IS_ALPHA;
-		}
-		for (int ch = 'a'; ch <= 'z'; ch++) {
-			FLAGS[ch] |= IS_ALPHA;
-		}
 	}
 
 
@@ -569,10 +562,7 @@ private boolean isDigit(char ch) {
 	}
 
 	private boolean isAlphabetic(char ch) {
-		if (ch > 255) {
-			return false;
-		}
-		return (FLAGS[ch] & IS_ALPHA) != 0;
+		return Character.isLetter(ch);
 	}
 
 	private boolean isHexadecimalDigit(char ch) {

spring-expression/src/test/java/org/springframework/expression/spel/ParsingTests.java

@@ -67,6 +67,20 @@ void supportedCharactersInIdentifiers() {
 			parseCheck("person_1.Age");
 			parseCheck("person_1.__age");
 			parseCheck("Person_1.get__age()");
+
+			// German characters
+			parseCheck("begrüssung");
+			parseCheck("#begrüssung");
+			parseCheck("begrüssung[1]", "begrüssung.[1]"); // extra "." is needed due to erroneous logic in CompoundExpression.toStringAST()
+			parseCheck("service.begrüssung");
+			parseCheck("service.getBegrüssung()");
+			parseCheck("Spaß");
+
+			// Spanish characters
+			parseCheck("buenos_sueños");
+
+			// Chinese characters
+			parseCheck("have乐趣()");
 		}
 
 		@Test
@@ -75,24 +89,6 @@ void unsupportedCharactersInIdentifiers() {
 			assertThatIllegalStateException()
 					.isThrownBy(() -> parser.parseRaw("apple~banana"))
 					.withMessage("Unsupported character '~' (126) encountered at position 6 in expression.");
-
-			// German characters
-			assertThatIllegalStateException()
-					.isThrownBy(() -> parser.parseRaw("begrüssung"))
-					.withMessage("Unsupported character 'ü' (252) encountered at position 5 in expression.");
-			assertThatIllegalStateException()
-					.isThrownBy(() -> parser.parseRaw("Spaß"))
-					.withMessage("Unsupported character 'ß' (223) encountered at position 4 in expression.");
-
-			// Spanish characters
-			assertThatIllegalStateException()
-					.isThrownBy(() -> parser.parseRaw("buenos_sueños"))
-					.withMessage("Unsupported character 'ñ' (241) encountered at position 11 in expression.");
-
-			// Chinese characters
-			assertThatIllegalStateException()
-					.isThrownBy(() -> parser.parseRaw("have乐趣()"))
-					.withMessage("Unsupported character '乐' (20048) encountered at position 5 in expression.");
 		}
 
 		@Test