Make maximum SpEL expression length configurable

Closes gh-30380

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

@@ -164,6 +164,24 @@ public abstract class AbstractExpressionTests {
 	 */
 	protected void evaluateAndCheckError(String expression, Class<?> expectedReturnType, SpelMessage expectedMessage,
 			Object... otherProperties) {
+
+		evaluateAndCheckError(this.parser, expression, expectedReturnType, expectedMessage, otherProperties);
+	}
+
+	/**
+	 * Evaluate the specified expression and ensure the expected message comes out.
+	 * The message may have inserts and they will be checked if otherProperties is specified.
+	 * The first entry in otherProperties should always be the position.
+	 * @param parser the expression parser to use
+	 * @param expression the expression to evaluate
+	 * @param expectedReturnType ask the expression return value to be of this type if possible
+	 * ({@code null} indicates don't ask for conversion)
+	 * @param expectedMessage the expected message
+	 * @param otherProperties the expected inserts within the message
+	 */
+	protected void evaluateAndCheckError(ExpressionParser parser, String expression, Class<?> expectedReturnType, SpelMessage expectedMessage,
+			Object... otherProperties) {
+
 		assertThatExceptionOfType(SpelEvaluationException.class).isThrownBy(() -> {
 			Expression expr = parser.parseExpression(expression);
 			assertThat(expr).as("expression").isNotNull();

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

@@ -77,6 +77,26 @@ class EvaluationTests extends AbstractExpressionTests {
 			evaluateAndCheckError(expression, String.class, SpelMessage.MAX_EXPRESSION_LENGTH_EXCEEDED);
 		}
 
+		@Test
+		void maxExpressionLengthIsConfigurable() {
+			int maximumExpressionLength = 20_000;
+
+			String expression = "'%s'".formatted("Y".repeat(19_998));
+			assertThat(expression).hasSize(maximumExpressionLength);
+
+			SpelParserConfiguration configuration =
+					new SpelParserConfiguration(null, null, false, false, 0, maximumExpressionLength);
+			ExpressionParser parser = new SpelExpressionParser(configuration);
+
+			Expression expr = parser.parseExpression(expression);
+			String result = expr.getValue(String.class);
+			assertThat(result).hasSize(19_998);
+
+			expression = "'%s'".formatted("Y".repeat(25_000));
+			assertThat(expression).hasSize(25_002);
+			evaluateAndCheckError(parser, expression, String.class, SpelMessage.MAX_EXPRESSION_LENGTH_EXCEEDED);
+		}
+
 		@Test
 		void createListsOnAttemptToIndexNull01() throws EvaluationException, ParseException {
 			ExpressionParser parser = new SpelExpressionParser(new SpelParserConfiguration(true, true));