Document the between operator in SpEL

Closes gh-32140

spring-expression/src/main/java/org/springframework/expression/spel/ast/OperatorBetween.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -26,12 +26,18 @@ import org.springframework.expression.spel.SpelMessage;
 import org.springframework.expression.spel.support.BooleanTypedValue;
 
 /**
- * Represents the between operator. The left operand to between must be a single value and
- * the right operand must be a list - this operator returns true if the left operand is
- * between (using the registered comparator) the two elements in the list. The definition
- * of between being inclusive follows the SQL BETWEEN definition.
+ * Represents the {@code between} operator.
+ *
+ * <p>The left operand must be a single value, and the right operand must be a
+ * 2-element list which defines the range.
+ *
+ * <p>This operator returns {@code true} if the left operand is between the two
+ * elements in the range, inclusive (using the registered {@link TypeComparator}
+ * for comparison). In addition, the first element in the range must be less than
+ * or equal to the second element in the range.
  *
  * @author Andy Clement
+ * @author Sam Brannen
  * @since 3.0
  */
 public class OperatorBetween extends Operator {

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

@@ -221,6 +221,7 @@ class SpelDocumentationTests extends AbstractExpressionTests {
 	void relationalOperators() {
 		boolean result = parser.parseExpression("2 == 2").getValue(Boolean.class);
 		assertThat(result).isTrue();
+
 		// evaluates to false
 		result = parser.parseExpression("2 < -5.0").getValue(Boolean.class);
 		assertThat(result).isFalse();
@@ -232,17 +233,47 @@ class SpelDocumentationTests extends AbstractExpressionTests {
 
 	@Test
 	void otherOperators() {
-		// evaluates to false
-		boolean falseValue = parser.parseExpression("'xyz' instanceof T(int)").getValue(Boolean.class);
-		assertThat(falseValue).isFalse();
+		boolean result;
 
 		// evaluates to true
-		boolean trueValue = parser.parseExpression("'5.00' matches '^-?\\d+(\\.\\d{2})?$'").getValue(Boolean.class);
-		assertThat(trueValue).isTrue();
+		result = parser.parseExpression(
+				"1 between {1, 5}").getValue(Boolean.class);
+		assertThat(result).isTrue();
 
-		//evaluates to false
-		falseValue = parser.parseExpression("'5.0067' matches '^-?\\d+(\\.\\d{2})?$'").getValue(Boolean.class);
-		assertThat(falseValue).isFalse();
+		// evaluates to false
+		result = parser.parseExpression(
+				"1 between {10, 15}").getValue(Boolean.class);
+		assertThat(result).isFalse();
+
+		// evaluates to true
+		result = parser.parseExpression(
+				"'elephant' between {'aardvark', 'zebra'}").getValue(Boolean.class);
+		assertThat(result).isTrue();
+
+		// evaluates to false
+		result = parser.parseExpression(
+				"'elephant' between {'aardvark', 'cobra'}").getValue(Boolean.class);
+		assertThat(result).isFalse();
+
+		// evaluates to true
+		result = parser.parseExpression(
+				"123 instanceof T(Integer)").getValue(Boolean.class);
+		assertThat(result).isTrue();
+
+		// evaluates to false
+		result = parser.parseExpression(
+				"'xyz' instanceof T(Integer)").getValue(Boolean.class);
+		assertThat(result).isFalse();
+
+		// evaluates to true
+		result = parser.parseExpression(
+				"'5.00' matches '^-?\\d+(\\.\\d{2})?$'").getValue(Boolean.class);
+		assertThat(result).isTrue();
+
+		// evaluates to false
+		result = parser.parseExpression(
+				"'5.0067' matches '^-?\\d+(\\.\\d{2})?$'").getValue(Boolean.class);
+		assertThat(result).isFalse();
 	}
 
 	@Test