Make max length of SpEL expressions in an ApplicationContext configurable

This commit introduces support for a Spring property named
`spring.context.expression.maxLength`. When set, the value of that
property is used internally in StandardBeanExpressionResolver to
configure the SpelParserConfiguration used when evaluating String
values in bean definitions, @⁠Value, etc.

Closes gh-31952

Author: sbrannen

framework-docs/modules/ROOT/pages/appendix.adoc

@@ -28,6 +28,11 @@ JavaBeans `Introspector`. See
 {spring-framework-api}++/beans/StandardBeanInfoFactory.html#IGNORE_BEANINFO_PROPERTY_NAME++[`CachedIntrospectionResults`]
 for details.
 
+| `spring.context.expression.maxLength`
+| The maximum length for
+xref:core/expressions/evaluation.adoc#expressions-parser-configuration[Spring Expression Language]
+expressions used in XML bean definitions, `@Value`, etc.
+
 | `spring.expression.compiler.mode`
 | The mode to use when compiling expressions for the
 xref:core/expressions/evaluation.adoc#expressions-compiler-configuration[Spring Expression Language].

framework-docs/modules/ROOT/pages/core/expressions/evaluation.adoc

@@ -380,6 +380,15 @@ Kotlin::
 ----
 ======
 
+By default, a SpEL expression cannot contain more than 10,000 characters; however, the
+`maxExpressionLength` is configurable. If you create a `SpelExpressionParser`
+programmatically, you can specify a custom `maxExpressionLength` when creating the
+`SpelParserConfiguration` that you provide to the `SpelExpressionParser`. If you wish to
+set the `maxExpressionLength` used for parsing SpEL expressions within an
+`ApplicationContext` -- for example, in XML bean definitions, `@Value`, etc. -- you can
+set a JVM system property or Spring property named `spring.context.expression.maxLength`
+to the maximum expression length needed by your application (see
+xref:appendix.adoc#appendix-spring-properties[Supported Spring Properties]).
 
 
 [[expressions-spel-compilation]]

spring-context/src/main/java/org/springframework/context/expression/StandardBeanExpressionResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 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.
@@ -23,6 +23,7 @@
 import org.springframework.beans.factory.BeanExpressionException;
 import org.springframework.beans.factory.config.BeanExpressionContext;
 import org.springframework.beans.factory.config.BeanExpressionResolver;
+import org.springframework.core.SpringProperties;
 import org.springframework.core.convert.ConversionService;
 import org.springframework.core.convert.support.DefaultConversionService;
 import org.springframework.expression.Expression;
@@ -47,6 +48,7 @@
  * beans such as "environment", "systemProperties" and "systemEnvironment".
  *
  * @author Juergen Hoeller
+ * @author Sam Brannen
  * @since 3.0
  * @see BeanExpressionContext#getBeanFactory()
  * @see org.springframework.expression.ExpressionParser
@@ -55,6 +57,14 @@
  */
 public class StandardBeanExpressionResolver implements BeanExpressionResolver {
 
+	/**
+	 * System property to configure the maximum length for SpEL expressions: {@value}.
+	 * <p>Can also be configured via the {@link SpringProperties} mechanism.
+	 * @since 6.1.3
+	 * @see SpelParserConfiguration#getMaximumExpressionLength()
+	 */
+	public static final String MAX_SPEL_EXPRESSION_LENGTH_PROPERTY_NAME = "spring.context.expression.maxLength";
+
 	/** Default expression prefix: "#{". */
 	public static final String DEFAULT_EXPRESSION_PREFIX = "#{";
 
@@ -90,18 +100,24 @@ public String getExpressionSuffix() {
 
 	/**
 	 * Create a new {@code StandardBeanExpressionResolver} with default settings.
+	 * <p>As of Spring Framework 6.1.3, the maximum SpEL expression length can be
+	 * configured via the {@link #MAX_SPEL_EXPRESSION_LENGTH_PROPERTY_NAME} property.
 	 */
 	public StandardBeanExpressionResolver() {
-		this.expressionParser = new SpelExpressionParser();
+		this(null);
 	}
 
 	/**
 	 * Create a new {@code StandardBeanExpressionResolver} with the given bean class loader,
 	 * using it as the basis for expression compilation.
+	 * <p>As of Spring Framework 6.1.3, the maximum SpEL expression length can be
+	 * configured via the {@link #MAX_SPEL_EXPRESSION_LENGTH_PROPERTY_NAME} property.
 	 * @param beanClassLoader the factory's bean class loader
 	 */
 	public StandardBeanExpressionResolver(@Nullable ClassLoader beanClassLoader) {
-		this.expressionParser = new SpelExpressionParser(new SpelParserConfiguration(null, beanClassLoader));
+		SpelParserConfiguration parserConfig = new SpelParserConfiguration(
+				null, beanClassLoader, false, false, Integer.MAX_VALUE, retrieveMaxExpressionLength());
+		this.expressionParser = new SpelExpressionParser(parserConfig);
 	}
 
 
@@ -178,4 +194,22 @@ public Object evaluate(@Nullable String value, BeanExpressionContext beanExpress
 	protected void customizeEvaluationContext(StandardEvaluationContext evalContext) {
 	}
 
+	private static int retrieveMaxExpressionLength() {
+		String value = SpringProperties.getProperty(MAX_SPEL_EXPRESSION_LENGTH_PROPERTY_NAME);
+		if (!StringUtils.hasText(value)) {
+			return SpelParserConfiguration.DEFAULT_MAX_EXPRESSION_LENGTH;
+		}
+
+		try {
+			int maxLength = Integer.parseInt(value.trim());
+			Assert.isTrue(maxLength > 0, () -> "Value [" + maxLength + "] for system property ["
+					+ MAX_SPEL_EXPRESSION_LENGTH_PROPERTY_NAME + "] must be positive");
+			return maxLength;
+		}
+		catch (NumberFormatException ex) {
+			throw new IllegalArgumentException("Failed to parse value for system property [" +
+					MAX_SPEL_EXPRESSION_LENGTH_PROPERTY_NAME + "]: " + ex.getMessage(), ex);
+		}
+	}
+
 }

spring-context/src/test/java/org/springframework/context/expression/ApplicationContextExpressionTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 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.
@@ -28,6 +28,7 @@
 
 import org.junit.jupiter.api.Test;
 
+import org.springframework.beans.factory.BeanCreationException;
 import org.springframework.beans.factory.ObjectFactory;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.beans.factory.annotation.Qualifier;
@@ -42,17 +43,24 @@
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
 import org.springframework.context.annotation.AnnotationConfigUtils;
 import org.springframework.context.support.GenericApplicationContext;
+import org.springframework.core.SpringProperties;
 import org.springframework.core.convert.support.DefaultConversionService;
 import org.springframework.core.convert.support.GenericConversionService;
 import org.springframework.core.io.ClassPathResource;
 import org.springframework.core.io.Resource;
 import org.springframework.core.io.support.EncodedResource;
 import org.springframework.core.testfixture.io.SerializationTestUtils;
+import org.springframework.expression.spel.SpelEvaluationException;
 import org.springframework.util.FileCopyUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
+import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
+import static org.springframework.context.expression.StandardBeanExpressionResolver.MAX_SPEL_EXPRESSION_LENGTH_PROPERTY_NAME;
 
 /**
+ * Integration tests for SpEL expression support in an {@code ApplicationContext}.
+ *
  * @author Juergen Hoeller
  * @author Sam Brannen
  * @since 3.0
@@ -268,6 +276,70 @@ void resourceInjection() throws IOException {
 		}
 	}
 
+	@Test
+	void maxSpelExpressionLengthMustBeAnInteger() {
+		doWithMaxSpelExpressionLength("boom", () -> {
+			try (AnnotationConfigApplicationContext ac = new AnnotationConfigApplicationContext()) {
+				assertThatIllegalArgumentException()
+						.isThrownBy(ac::refresh)
+						.withMessageStartingWith("Failed to parse value for system property [%s]",
+								MAX_SPEL_EXPRESSION_LENGTH_PROPERTY_NAME)
+						.withMessageContaining("boom");
+			}
+		});
+	}
+
+	@Test
+	void maxSpelExpressionLengthMustBePositive() {
+		doWithMaxSpelExpressionLength("-99", () -> {
+			try (AnnotationConfigApplicationContext ac = new AnnotationConfigApplicationContext()) {
+				assertThatIllegalArgumentException()
+						.isThrownBy(ac::refresh)
+						.withMessage("Value [%d] for system property [%s] must be positive", -99,
+								MAX_SPEL_EXPRESSION_LENGTH_PROPERTY_NAME);
+			}
+		});
+	}
+
+	@Test
+	void maxSpelExpressionLength() {
+		final String expression = "#{ 'xyz' + 'xyz' + 'xyz' }";
+
+		// With the default max length of 10_000, the expression should succeed.
+		evaluateExpressionInBean(expression);
+
+		// With a max length of 20, the expression should fail.
+		doWithMaxSpelExpressionLength("20", () ->
+				assertThatExceptionOfType(BeanCreationException.class)
+					.isThrownBy(() -> evaluateExpressionInBean(expression))
+					.havingRootCause()
+						.isInstanceOf(SpelEvaluationException.class)
+						.withMessageEndingWith("exceeding the threshold of '20' characters"));
+	}
+
+	private static void doWithMaxSpelExpressionLength(String maxLength, Runnable action) {
+		try {
+			SpringProperties.setProperty(MAX_SPEL_EXPRESSION_LENGTH_PROPERTY_NAME, maxLength);
+			action.run();
+		}
+		finally {
+			SpringProperties.setProperty(MAX_SPEL_EXPRESSION_LENGTH_PROPERTY_NAME, null);
+		}
+	}
+
+	private static void evaluateExpressionInBean(String expression) {
+		try (AnnotationConfigApplicationContext ac = new AnnotationConfigApplicationContext()) {
+			GenericBeanDefinition bd = new GenericBeanDefinition();
+			bd.setBeanClass(String.class);
+			bd.getConstructorArgumentValues().addGenericArgumentValue(expression);
+			ac.registerBeanDefinition("str", bd);
+			ac.refresh();
+
+			String str = ac.getBean("str", String.class);
+			assertThat(str).isEqualTo("xyz".repeat(3)); // "#{ 'xyz' + 'xyz' + 'xyz' }"
+		}
+	}
+
 
 	@SuppressWarnings("serial")
 	public static class ValueTestBean implements Serializable {

spring-expression/src/main/java/org/springframework/expression/spel/SpelParserConfiguration.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 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.
@@ -35,7 +35,7 @@ public class SpelParserConfiguration {
 	 * Default maximum length permitted for a SpEL expression.
 	 * @since 5.2.24
 	 */
-	private static final int DEFAULT_MAX_EXPRESSION_LENGTH = 10_000;
+	public static final int DEFAULT_MAX_EXPRESSION_LENGTH = 10_000;
 
 	/** System property to configure the default compiler mode for SpEL expression parsers: {@value}. */
 	public static final String SPRING_EXPRESSION_COMPILER_MODE_PROPERTY_NAME = "spring.expression.compiler.mode";