Initial review and polish of IndexAccessor support in SpEL

See gh-26409
See gh-26478

spring-expression/spring-expression.gradle

@@ -9,5 +9,4 @@ dependencies {
 	testImplementation("org.jetbrains.kotlin:kotlin-reflect")
 	testImplementation("org.jetbrains.kotlin:kotlin-stdlib")
 	testImplementation("com.fasterxml.jackson.core:jackson-databind")
-	testImplementation("com.fasterxml.jackson.core:jackson-core")
 }

spring-expression/src/main/java/org/springframework/expression/EvaluationContext.java

@@ -16,6 +16,7 @@
 
 package org.springframework.expression;
 
+import java.util.Collections;
 import java.util.List;
 import java.util.function.Supplier;
 
@@ -57,9 +58,14 @@ public interface EvaluationContext {
 	List<PropertyAccessor> getPropertyAccessors();
 
 	/**
-	 * Return a list of index accessors that will be asked in turn to read/write a property.
+	 * Return a list of index accessors that will be asked in turn to access or
+	 * set an indexed value.
+	 * <p>The default implementation returns an empty list.
+	 * @since 6.2
 	 */
-	List<IndexAccessor> getIndexAccessors();
+	default List<IndexAccessor> getIndexAccessors() {
+		return Collections.emptyList();
+	}
 
 	/**
 	 * Return a list of resolvers that will be asked in turn to locate a constructor.

spring-expression/src/main/java/org/springframework/expression/IndexAccessor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 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.
@@ -20,78 +20,91 @@ import org.springframework.expression.spel.ast.ValueRef;
 import org.springframework.lang.Nullable;
 
 /**
- * A index accessor is able to read from (and possibly write to) an array's elements.
+ * An index accessor is able to read from (and possibly write to) an indexed
+ * structure of an object.
  *
- * <p>This interface places no restrictions, and so implementors are free to access elements
- * directly as fields or through getters or in any other way they see as appropriate.
+ * <p>This interface places no restrictions on what constitutes an indexed
+ * structure. Implementors are therefore free to access indexed values any way
+ * they deem appropriate.
  *
- * <p>A resolver can optionally specify an array of target classes for which it should be
- * called. However, if it returns {@code null} from {@link #getSpecificTargetClasses()},
- * it will be called for all property references and given a chance to determine if it
- * can read or write them.
+ * <p>An index accessor can optionally specify an array of target classes for
+ * which it should be called. However, if it returns {@code null} or an empty
+ * array from {@link #getSpecificTargetClasses()}, it will be called for all
+ * indexing operations and given a chance to determine if it can read from or
+ * write to the indexed structure.
  *
- * <p>Property resolvers are considered to be ordered, and each will be called in turn.
- * The only rule that affects the call order is that any resolver naming the target
- * class directly in {@link #getSpecificTargetClasses()} will be called first, before
- * the general resolvers.
+ * <p>Index accessors are considered to be ordered, and each will be called in
+ * turn. The only rule that affects the call order is that any index accessor
+ * which specifies explicit support for the target class via
+ * {@link #getSpecificTargetClasses()} will be called first, before other
+ * generic index accessors.
  *
- * @author jackmiking lee
- * @since 3.0
+ * @author Jackmiking Lee
+ * @author Sam Brannen
+ * @since 6.2
+ * @see PropertyAccessor
  */
-public interface IndexAccessor {
+public interface IndexAccessor extends TargetedAccessor {
+
 	/**
-	 * Return an array of classes for which this resolver should be called.
-	 * <p>Returning {@code null} indicates this is a general resolver that
-	 * can be called in an attempt to resolve a property on any type.
-	 * @return an array of classes that this resolver is suitable for
-	 * (or {@code null} if a general resolver)
+	 * Get the set of classes for which this index accessor should be called.
+	 * <p>Returning {@code null} or an empty array indicates this is a generic
+	 * index accessor that can be called in an attempt to access an index on any
+	 * type.
+	 * @return an array of classes that this index accessor is suitable for
+	 * (or {@code null} or an empty array if a generic index accessor)
 	 */
+	@Override
 	@Nullable
 	Class<?>[] getSpecificTargetClasses();
 
 	/**
-	 * Called to determine if a resolver instance is able to access a specified property
-	 * on a specified target object.
+	 * Called to determine if this index accessor is able to read a specified
+	 * index on a specified target object.
 	 * @param context the evaluation context in which the access is being attempted
-	 * @param target the target object upon which the property is being accessed
-	 * @param index the index of the array being accessed
-	 * @return true if this resolver is able to read the property
-	 * @throws AccessException if there is any problem determining whether the property can be read
+	 * @param target the target object upon which the index is being accessed
+	 * @param index the index being accessed
+	 * @return true if this index accessor is able to read the index
+	 * @throws AccessException if there is any problem determining whether the
+	 * index can be read
 	 */
 	boolean canRead(EvaluationContext context, @Nullable Object target, Object index) throws AccessException;
 
 	/**
-	 * Called to read a property from a specified target object.
-	 * Should only succeed if {@link #canRead} also returns {@code true}.
+	 * Called to read an index from a specified target object.
+	 * <p>Should only succeed if {@link #canRead} also returns {@code true}.
 	 * @param context the evaluation context in which the access is being attempted
-	 * @param target the target object upon which the property is being accessed
-	 * @param index the index of the array being accessed
-	 * @return a TypedValue object wrapping the property value read and a type descriptor for it
-	 * @throws AccessException if there is any problem accessing the property value
+	 * @param target the target object upon which the index is being accessed
+	 * @param index the index being accessed
+	 * @return a TypedValue object wrapping the index value read and a type
+	 * descriptor for it
+	 * @throws AccessException if there is any problem reading the index value
 	 */
-	ValueRef read(EvaluationContext context, @Nullable Object target,Object index) throws AccessException;
+	// TODO Change return type to TypedValue to avoid package cycle.
+	ValueRef read(EvaluationContext context, @Nullable Object target, Object index) throws AccessException;
 
 	/**
-	 * Called to determine if a resolver instance is able to write to a specified
-	 * property on a specified target object.
+	 * Called to determine if this index accessor is able to write to a specified
+	 * index on a specified target object.
 	 * @param context the evaluation context in which the access is being attempted
-	 * @param target the target object upon which the property is being accessed
-	 * @param index the index of the array being accessed
-	 * @return true if this resolver is able to write to the property
+	 * @param target the target object upon which the index is being accessed
+	 * @param index the index being accessed
+	 * @return true if this index accessor is able to write to the index
 	 * @throws AccessException if there is any problem determining whether the
-	 * property can be written to
+	 * index can be written to
 	 */
 	boolean canWrite(EvaluationContext context, @Nullable Object target, Object index) throws AccessException;
 
 	/**
-	 * Called to write to a property on a specified target object.
-	 * Should only succeed if {@link #canWrite} also returns {@code true}.
+	 * Called to write to an index on a specified target object.
+	 * <p>Should only succeed if {@link #canWrite} also returns {@code true}.
 	 * @param context the evaluation context in which the access is being attempted
-	 * @param target the target object upon which the property is being accessed
-	 * @param index the index of the array being accessed
-	 * @param newValue the new value for the property
-	 * @throws AccessException if there is any problem writing to the property value
+	 * @param target the target object upon which the index is being accessed
+	 * @param index the index being accessed
+	 * @param newValue the new value for the index
+	 * @throws AccessException if there is any problem writing to the index value
 	 */
 	void write(EvaluationContext context, @Nullable Object target, Object index, @Nullable Object newValue)
 			throws AccessException;
+
 }

spring-expression/src/main/java/org/springframework/expression/PropertyAccessor.java

@@ -34,21 +34,24 @@ import org.springframework.lang.Nullable;
  * <p>Property accessors are considered to be ordered, and each will be called in
  * turn. The only rule that affects the call order is that any property accessor
  * which specifies explicit support for the target class via
- * {@link #getSpecificTargetClasses()} will be called first, before the general
+ * {@link #getSpecificTargetClasses()} will be called first, before the generic
  * property accessors.
  *
  * @author Andy Clement
  * @since 3.0
+ * @see IndexAccessor
  */
-public interface PropertyAccessor {
+public interface PropertyAccessor extends TargetedAccessor {
 
 	/**
-	 * Return an array of classes for which this property accessor should be called.
-	 * <p>Returning {@code null} indicates this is a general property accessor that
-	 * can be called in an attempt to access a property on any type.
+	 * Get the set of classes for which this property accessor should be called.
+	 * <p>Returning {@code null} or an empty array indicates this is a generic
+	 * property accessor that can be called in an attempt to access a property on
+	 * any type.
 	 * @return an array of classes that this property accessor is suitable for
-	 * (or {@code null} if a general property accessor)
+	 * (or {@code null} if a generic property accessor)
 	 */
+	@Override
 	@Nullable
 	Class<?>[] getSpecificTargetClasses();
 

spring-expression/src/main/java/org/springframework/expression/TargetedAccessor.java

@@ -0,0 +1,56 @@
+/*
+ * 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.expression;
+
+import org.springframework.lang.Nullable;
+
+/**
+ * Strategy for types that access elements of specific target classes.
+ *
+ * <p>This interface places no restrictions on what constitutes an element.
+ *
+ * <p>A targeted accessor can specify a set of target classes for which it should
+ * be called. However, if it returns {@code null} or an empty array from
+ * {@link #getSpecificTargetClasses()}, it will typically be called for all
+ * access operations and given a chance to determine if it supports a concrete
+ * access attempt.
+ *
+ * <p>Targeted accessors are considered to be ordered, and each will be called
+ * in turn. The only rule that affects the call order is that any accessor which
+ * specifies explicit support for a given target class via
+ * {@link #getSpecificTargetClasses()} will be called first, before other generic
+ * accessors that do not specify explicit support for the given target class.
+ *
+ * @author Sam Brannen
+ * @since 6.2
+ * @see PropertyAccessor
+ * @see IndexAccessor
+ */
+public interface TargetedAccessor {
+
+	/**
+	 * Get the set of classes for which this accessor should be called.
+	 * <p>Returning {@code null} or an empty array indicates this is a generic
+	 * accessor that can be called in an attempt to access an element on any
+	 * type.
+	 * @return an array of classes that this accessor is suitable for
+	 * (or {@code null} or an empty array if a generic accessor)
+	 */
+	@Nullable
+	Class<?>[] getSpecificTargetClasses();
+
+}

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

@@ -17,9 +17,11 @@
 package org.springframework.expression.spel.ast;
 
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 
 import org.springframework.expression.PropertyAccessor;
+import org.springframework.expression.TargetedAccessor;
 import org.springframework.lang.Nullable;
 import org.springframework.util.ObjectUtils;
 
@@ -27,16 +29,76 @@ import org.springframework.util.ObjectUtils;
  * Utility methods for use in the AST classes.
  *
  * @author Andy Clement
+ * @author Sam Brannen
  * @since 3.0.2
  */
 public abstract class AstUtils {
 
+	/**
+	 * Determine the set of accessors that should be used to try to access an
+	 * element on the specified target type.
+	 * <p>The accessors are considered to be in an ordered list; however, in the
+	 * returned list any accessors that are exact matches for the input target
+	 * type (as opposed to 'generic' accessors that could work for any type) are
+	 * placed at the start of the list. In addition, if there are specific
+	 * accessors that exactly name the class in question and accessors that name
+	 * a specific class which is a supertype of the class in question, the latter
+	 * are put at the end of the specific accessors set and will be tried after
+	 * exactly matching accessors but before generic accessors.
+	 * @param targetType the type upon which element access is being attempted
+	 * @param accessors the list of element accessors to process
+	 * @return a list of accessors that should be tried in order to access the
+	 * element on the specified target type, or an empty list if no suitable
+	 * accessor could be found
+	 * @since 6.2
+	 */
+	public static <T extends TargetedAccessor> List<T> getAccessorsToTry(
+			@Nullable Class<?> targetType, List<T> accessors) {
+
+		if (accessors.isEmpty()) {
+			return Collections.emptyList();
+		}
+
+		List<T> exactMatches = new ArrayList<>();
+		List<T> inexactMatches = new ArrayList<>();
+		List<T> genericMatches = new ArrayList<>();
+		for (T accessor : accessors) {
+			Class<?>[] targets = accessor.getSpecificTargetClasses();
+			if (ObjectUtils.isEmpty(targets)) {
+				// generic accessor that says it can be used for any type
+				genericMatches.add(accessor);
+			}
+			else if (targetType != null) {
+				for (Class<?> clazz : targets) {
+					if (clazz == targetType) {
+						exactMatches.add(accessor);
+					}
+					else if (clazz.isAssignableFrom(targetType)) {
+						inexactMatches.add(accessor);
+					}
+				}
+			}
+		}
+
+		int size = exactMatches.size() + inexactMatches.size() + genericMatches.size();
+		if (size == 0) {
+			return Collections.emptyList();
+		}
+		else {
+			List<T> result = new ArrayList<>(size);
+			result.addAll(exactMatches);
+			result.addAll(inexactMatches);
+			result.addAll(genericMatches);
+			return result;
+		}
+	}
+
 	/**
 	 * Determine the set of property accessors that should be used to try to
 	 * access a property on the specified target type.
 	 * <p>The accessors are considered to be in an ordered list; however, in the
 	 * returned list any accessors that are exact matches for the input target
-	 * type (as opposed to 'general' accessors that could work for any type) are
+	 * type (as opposed to 'generic' accessors that could work for any type) are
 	 * placed at the start of the list. In addition, if there are specific
 	 * accessors that exactly name the class in question and accessors that name
 	 * a specific class which is a supertype of the class in question, the latter
@@ -44,36 +106,15 @@ public abstract class AstUtils {
 	 * exactly matching accessors but before generic accessors.
 	 * @param targetType the type upon which property access is being attempted
 	 * @param propertyAccessors the list of property accessors to process
-	 * @return a list of accessors that should be tried in order to access the property
+	 * @return a list of accessors that should be tried in order to access the
+	 * property on the specified target type, or an empty list if no suitable
+	 * accessor could be found
+	 * @see #getAccessorsToTry(Class, List)
 	 */
 	public static List<PropertyAccessor> getPropertyAccessorsToTry(
 			@Nullable Class<?> targetType, List<PropertyAccessor> propertyAccessors) {
 
-		List<PropertyAccessor> specificAccessors = new ArrayList<>();
-		List<PropertyAccessor> generalAccessors = new ArrayList<>();
-		for (PropertyAccessor accessor : propertyAccessors) {
-			Class<?>[] targets = accessor.getSpecificTargetClasses();
-			if (ObjectUtils.isEmpty(targets)) {
-				// generic accessor that says it can be used for any type
-				generalAccessors.add(accessor);
-			}
-			else if (targetType != null) {
-				for (Class<?> clazz : targets) {
-					if (clazz == targetType) {
-						// add exact matches to the specificAccessors list
-						specificAccessors.add(accessor);
-					}
-					else if (clazz.isAssignableFrom(targetType)) {
-						// add supertype matches to the front of the generalAccessors list
-						generalAccessors.add(0, accessor);
-					}
-				}
-			}
-		}
-		List<PropertyAccessor> accessors = new ArrayList<>(specificAccessors.size() + generalAccessors.size());
-		accessors.addAll(specificAccessors);
-		accessors.addAll(generalAccessors);
-		return accessors;
+		return getAccessorsToTry(targetType, propertyAccessors);
 	}
 
 }

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

@@ -17,11 +17,9 @@
 package org.springframework.expression.spel.ast;
 
 import java.lang.reflect.Constructor;
-import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
 import java.util.Map;
-import java.util.Optional;
 import java.util.function.Supplier;
 
 import org.springframework.asm.Label;
@@ -160,6 +158,7 @@ public class Indexer extends SpelNodeImpl {
 			throws EvaluationException {
 
 		TypedValue typedValue = valueSupplier.get();
+		// TODO Set value for IndexAccessor via its write() method, NOT via the ValueRef returned from its read() method.
 		getValueRef(state).setValue(typedValue.getValue());
 		return typedValue;
 	}
@@ -249,73 +248,25 @@ public class Indexer extends SpelNodeImpl {
 			return new PropertyIndexingValueRef(
 					target, (String) index, state.getEvaluationContext(), targetDescriptor);
 		}
-		Optional<ValueRef> optional = tryIndexAccessor(state, index);
-		if (optional.isPresent()) {
-			return optional.get();
+
+		EvaluationContext evalContext = state.getEvaluationContext();
+		List<IndexAccessor> accessorsToTry = getIndexAccessorsToTry(target, evalContext.getIndexAccessors());
+		try {
+			for (IndexAccessor indexAccessor : accessorsToTry) {
+				if (indexAccessor.canRead(evalContext, target, index)) {
+					// TODO Introduce local IndexAccessorValueRef.
+					return indexAccessor.read(evalContext, target, index);
+				}
+			}
 		}
+		catch (Exception ex) {
+			// TODO throw SpelEvaluationException for "exception during index access"
+		}
+
 		throw new SpelEvaluationException(
 				getStartPosition(), SpelMessage.INDEXING_NOT_SUPPORTED_FOR_TYPE, targetDescriptor);
 	}
 
-	private Optional<ValueRef> tryIndexAccessor(ExpressionState state, Object index) {
-		EvaluationContext context = state.getEvaluationContext();
-		Object target = state.getActiveContextObject().getValue();
-		if (context != null) {
-			List<IndexAccessor> list = context.getIndexAccessors();
-			if (list != null) {
-				List<IndexAccessor> availableAccessors = getIndexAccessorsToTry(state.getActiveContextObject(), list);
-				try {
-					for (IndexAccessor indexAccessor : availableAccessors) {
-						if (indexAccessor.canRead(context, target, index)) {
-							ValueRef valueRef = indexAccessor.read(context, target, index);
-							return Optional.of(valueRef);
-						}
-					}
-				}
-				catch (Exception ex) {
-				}
-			}
-		}
-		return Optional.empty();
-	}
-
-	private List<IndexAccessor> getIndexAccessorsToTry(
-			@Nullable Object contextObject, List<IndexAccessor> propertyAccessors) {
-
-		Class<?> targetType;
-		if (contextObject instanceof TypedValue) {
-			targetType = ((TypedValue) contextObject).getTypeDescriptor().getObjectType();
-		}
-		else {
-			targetType = (contextObject != null ? contextObject.getClass() : null);
-		}
-
-		List<IndexAccessor> specificAccessors = new ArrayList<>();
-		List<IndexAccessor> generalAccessors = new ArrayList<>();
-		for (IndexAccessor resolver : propertyAccessors) {
-			Class<?>[] targets = resolver.getSpecificTargetClasses();
-			if (targets == null) {
-				// generic resolver that says it can be used for any type
-				generalAccessors.add(resolver);
-			}
-			else if (targetType != null) {
-				for (Class<?> clazz : targets) {
-					if (clazz == targetType) {
-						specificAccessors.add(resolver);
-						break;
-					}
-					else if (clazz.isAssignableFrom(targetType)) {
-						generalAccessors.add(resolver);
-					}
-				}
-			}
-		}
-		List<IndexAccessor> resolvers = new ArrayList<>(specificAccessors);
-		generalAccessors.removeAll(specificAccessors);
-		resolvers.addAll(generalAccessors);
-		return resolvers;
-	}
-
 	@Override
 	public boolean isCompilable() {
 		if (this.indexedType == IndexedType.ARRAY) {
@@ -451,6 +402,22 @@ public class Indexer extends SpelNodeImpl {
 		}
 	}
 
+	/**
+	 * Determine the set of index accessors that should be used to try to access
+	 * an index on the specified context object.
+	 * <p>Delegates to {@link AstUtils#getAccessorsToTry(Class, List)}.
+	 * @param targetObject the object upon which index access is being attempted
+	 * @param indexAccessors the list of index accessors to process
+	 * @return a list of accessors that should be tried in order to access the
+	 * index, or an empty list if no suitable accessor could be found
+	 */
+	private static List<IndexAccessor> getIndexAccessorsToTry(
+			@Nullable Object targetObject, List<IndexAccessor> indexAccessors) {
+
+		Class<?> targetType = (targetObject != null ? targetObject.getClass() : null);
+		return AstUtils.getAccessorsToTry(targetType, indexAccessors);
+	}
+
 
 	private class ArrayIndexingValueRef implements ValueRef {
 

spring-expression/src/main/java/org/springframework/expression/spel/support/SimpleEvaluationContext.java

@@ -28,7 +28,6 @@ import org.springframework.core.convert.TypeDescriptor;
 import org.springframework.expression.BeanResolver;
 import org.springframework.expression.ConstructorResolver;
 import org.springframework.expression.EvaluationContext;
-import org.springframework.expression.IndexAccessor;
 import org.springframework.expression.MethodResolver;
 import org.springframework.expression.OperatorOverloader;
 import org.springframework.expression.PropertyAccessor;
@@ -147,11 +146,6 @@ public final class SimpleEvaluationContext implements EvaluationContext {
 		return this.propertyAccessors;
 	}
 
-	@Override
-	public List<IndexAccessor> getIndexAccessors() {
-		return null;
-	}
-
 	/**
 	 * Return an empty list, always, since this context does not support the
 	 * use of type references.

spring-expression/src/main/java/org/springframework/expression/spel/support/StandardEvaluationContext.java

@@ -146,10 +146,6 @@ public class StandardEvaluationContext implements EvaluationContext {
 		this.propertyAccessors = propertyAccessors;
 	}
 
-	public void setIndexAccessors(List<IndexAccessor>indexAccessors){
-		this.indexAccessors=indexAccessors;
-	}
-
 	@Override
 	public List<PropertyAccessor> getPropertyAccessors() {
 		return initPropertyAccessors();
@@ -163,11 +159,53 @@ public class StandardEvaluationContext implements EvaluationContext {
 		return initPropertyAccessors().remove(accessor);
 	}
 
-	public void addIndexAccessor(IndexAccessor accessor){
-		initIndexAccessors().add(accessor);
+	/**
+	 * Set the list of index accessors to use in this evaluation context.
+	 * <p>Replaces any previously configured index accessors.
+	 * @since 6.2
+	 * @see #getIndexAccessors()
+	 * @see #addIndexAccessor(IndexAccessor)
+	 * @see #removeIndexAccessor(IndexAccessor)
+	 */
+	public void setIndexAccessors(List<IndexAccessor> indexAccessors) {
+		this.indexAccessors = indexAccessors;
 	}
 
-	public boolean removeIndexAccessor(IndexAccessor indexAccessor){
+	/**
+	 * Get the list of index accessors configured in this evaluation context.
+	 * @since 6.2
+	 * @see #setIndexAccessors(List)
+	 * @see #addIndexAccessor(IndexAccessor)
+	 * @see #removeIndexAccessor(IndexAccessor)
+	 */
+	@Override
+	public List<IndexAccessor> getIndexAccessors() {
+		return initIndexAccessors();
+	}
+
+	/**
+	 * Add the supplied index accessor to this evaluation context.
+	 * @param indexAccessor the index accessor to add
+	 * @since 6.2
+	 * @see #getIndexAccessors()
+	 * @see #setIndexAccessors(List)
+	 * @see #removeIndexAccessor(IndexAccessor)
+	 */
+	public void addIndexAccessor(IndexAccessor indexAccessor) {
+		initIndexAccessors().add(indexAccessor);
+	}
+
+	/**
+	 * Remove the supplied index accessor from this evaluation context.
+	 * @param indexAccessor the index accessor to remove
+	 * @return {@code true} if the index accessor was removed, {@code false} if
+	 * the index accessor was not configured in this evaluation context
+	 * @since 6.2
+	 * @see #getIndexAccessors()
+	 * @see #setIndexAccessors(List)
+	 * @see #addIndexAccessor(IndexAccessor)
+	 */
+	public boolean removeIndexAccessor(IndexAccessor indexAccessor) {
 		return initIndexAccessors().remove(indexAccessor);
 	}
 
@@ -400,6 +438,7 @@ public class StandardEvaluationContext implements EvaluationContext {
 		evaluationContext.setConstructorResolvers(new ArrayList<>(getConstructorResolvers()));
 		evaluationContext.setMethodResolvers(new ArrayList<>(getMethodResolvers()));
 		evaluationContext.setPropertyAccessors(new ArrayList<>(getPropertyAccessors()));
+		evaluationContext.setIndexAccessors(new ArrayList<>(getIndexAccessors()));
 		evaluationContext.setTypeLocator(getTypeLocator());
 		evaluationContext.setTypeConverter(getTypeConverter());
 
@@ -420,9 +459,9 @@ public class StandardEvaluationContext implements EvaluationContext {
 		return accessors;
 	}
 
-	private List<IndexAccessor>initIndexAccessors(){
+	private List<IndexAccessor> initIndexAccessors() {
 		List<IndexAccessor> accessors = this.indexAccessors;
-		if(accessors == null){
+		if (accessors == null) {
 			accessors = new ArrayList<>(5);
 			this.indexAccessors = accessors;
 		}
@@ -454,9 +493,4 @@ public class StandardEvaluationContext implements EvaluationContext {
 		list.add(list.size() - 1, element);
 	}
 
-	@Override
-	public List<IndexAccessor> getIndexAccessors() {
-		return initIndexAccessors();
-	}
-
 }

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

@@ -28,13 +28,20 @@ import java.util.List;
 import java.util.Map;
 import java.util.Set;
 
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.node.ArrayNode;
+import com.fasterxml.jackson.databind.node.NullNode;
+import com.fasterxml.jackson.databind.node.TextNode;
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.expression.EvaluationContext;
 import org.springframework.expression.Expression;
+import org.springframework.expression.IndexAccessor;
 import org.springframework.expression.PropertyAccessor;
 import org.springframework.expression.TypedValue;
+import org.springframework.expression.spel.ast.ValueRef;
 import org.springframework.expression.spel.standard.SpelExpressionParser;
 import org.springframework.expression.spel.support.StandardEvaluationContext;
 import org.springframework.expression.spel.testresources.Person;
@@ -449,6 +456,135 @@ class IndexingTests {
 
 	}
 
+	@Nested
+	class IndexAccessorTests {  // gh-26478
+
+		@Test
+		void addingAndRemovingIndexAccessors() {
+			ObjectMapper objectMapper = new ObjectMapper();
+			IndexAccessor accessor1 = new JacksonArrayNodeIndexAccessor(objectMapper);
+			IndexAccessor accessor2 = new JacksonArrayNodeIndexAccessor(objectMapper);
+
+			StandardEvaluationContext context = new StandardEvaluationContext();
+			List<IndexAccessor> indexAccessors = context.getIndexAccessors();
+			assertThat(indexAccessors).isEmpty();
+
+			context.addIndexAccessor(accessor1);
+			assertThat(indexAccessors).containsExactly(accessor1);
+
+			context.addIndexAccessor(accessor2);
+			assertThat(indexAccessors).containsExactly(accessor1, accessor2);
+
+			List<IndexAccessor> copy = new ArrayList<>(indexAccessors);
+			assertThat(context.removeIndexAccessor(accessor1)).isTrue();
+			assertThat(context.removeIndexAccessor(accessor1)).isFalse();
+			assertThat(indexAccessors).containsExactly(accessor2);
+
+			context.setIndexAccessors(copy);
+			assertThat(context.getIndexAccessors()).containsExactly(accessor1, accessor2);
+		}
+
+		@Test
+		void indexReadWrite() {
+			StandardEvaluationContext context = new StandardEvaluationContext();
+
+			ObjectMapper objectMapper = new ObjectMapper();
+			context.addIndexAccessor(new JacksonArrayNodeIndexAccessor(objectMapper));
+
+			TextNode node0 = new TextNode("node0");
+			TextNode node1 = new TextNode("node1");
+			ArrayNode arrayNode = objectMapper.createArrayNode();
+			arrayNode.addAll(List.of(node0, node1));
+
+			SpelExpressionParser parser = new SpelExpressionParser();
+			Expression expr = parser.parseExpression("[0]");
+			assertThat(expr.getValue(context, arrayNode)).isSameAs(node0);
+
+			TextNode nodeX = new TextNode("nodeX");
+			expr.setValue(context, arrayNode, nodeX);
+			// We use isEqualTo() instead of isSameAs(), since ObjectMapper.convertValue()
+			// converts the supplied TextNode to an equivalent JsonNode.
+			assertThat(expr.getValue(context, arrayNode)).isEqualTo(nodeX);
+
+			NullNode nullNode = NullNode.getInstance();
+			expr.setValue(context, arrayNode, nullNode);
+			assertThat(expr.getValue(context, arrayNode)).isSameAs(nullNode);
+
+			expr = parser.parseExpression("[1]");
+			assertThat(expr.getValue(context, arrayNode)).isSameAs(node1);
+
+			expr = parser.parseExpression("[-1]");
+			// Jackson's ArrayNode returns null for a non-existent index instead
+			// of throwing an ArrayIndexOutOfBoundsException or similar.
+			assertThat(expr.getValue(context, arrayNode)).isNull();
+		}
+
+
+		/**
+		 * {@link IndexAccessor} that knows how to read and write indexes in a
+		 * Jackson {@link ArrayNode}.
+		 */
+		private static class JacksonArrayNodeIndexAccessor implements IndexAccessor {
+
+			private final ObjectMapper objectMapper;
+
+			JacksonArrayNodeIndexAccessor(ObjectMapper objectMapper) {
+				this.objectMapper = objectMapper;
+			}
+
+			@Override
+			public Class<?>[] getSpecificTargetClasses() {
+				return new Class[] { ArrayNode.class };
+			}
+
+			@Override
+			public boolean canRead(EvaluationContext context, Object target, Object index) {
+				return (target instanceof ArrayNode && index instanceof Integer);
+			}
+
+			@Override
+			public ValueRef read(EvaluationContext context, Object target, Object index) {
+				return new ArrayNodeValueRef((ArrayNode) target, (Integer) index, this.objectMapper);
+			}
+
+			@Override
+			public boolean canWrite(EvaluationContext context, Object target, Object index) {
+				return (target instanceof ArrayNode && index instanceof Integer);
+			}
+
+			@Override
+			public void write(EvaluationContext context, Object target, Object index, Object newValue) {
+				if (!(target instanceof ArrayNode arrayNode)) {
+					throw new IllegalStateException("target must be an ArrayNode: " + target.getClass().getName());
+				}
+				if (!(index instanceof Integer intIndex)) {
+					throw new IllegalStateException("index must be an integer: " + target.getClass().getName());
+				}
+
+				arrayNode.set(intIndex, this.objectMapper.convertValue(newValue, JsonNode.class));
+			}
+
+			private record ArrayNodeValueRef(ArrayNode arrayNode, int index, ObjectMapper objectMapper) implements ValueRef {
+
+				@Override
+				public TypedValue getValue() {
+					return new TypedValue(this.arrayNode.get(this.index));
+				}
+
+				@Override
+				public void setValue(Object newValue) {
+					// TODO throw new UnsupportedOperationException("setValue() is not supported");
+					this.arrayNode.set(index, this.objectMapper.convertValue(newValue, JsonNode.class));
+				}
+
+				@Override
+				public boolean isWritable() {
+					return true;
+				}
+			}
+		}
+	}
+
 
 	@Target({ElementType.FIELD})
 	@Retention(RetentionPolicy.RUNTIME)

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

@@ -21,10 +21,6 @@ import java.util.Collections;
 import java.util.List;
 import java.util.Map;
 
-import com.fasterxml.jackson.databind.JsonNode;
-import com.fasterxml.jackson.databind.ObjectMapper;
-import com.fasterxml.jackson.databind.node.ArrayNode;
-import com.fasterxml.jackson.databind.node.TextNode;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.core.convert.TypeDescriptor;
@@ -32,10 +28,8 @@ import org.springframework.expression.AccessException;
 import org.springframework.expression.EvaluationContext;
 import org.springframework.expression.EvaluationException;
 import org.springframework.expression.Expression;
-import org.springframework.expression.IndexAccessor;
 import org.springframework.expression.PropertyAccessor;
 import org.springframework.expression.TypedValue;
-import org.springframework.expression.spel.ast.ValueRef;
 import org.springframework.expression.spel.standard.SpelExpression;
 import org.springframework.expression.spel.standard.SpelExpressionParser;
 import org.springframework.expression.spel.support.SimpleEvaluationContext;
@@ -150,25 +144,6 @@ class PropertyAccessTests extends AbstractExpressionTests {
 		assertThat(ctx.getPropertyAccessors()).hasSize(2);
 	}
 
-	@Test
-	public void testAddingRemovingIndexAccessors() {
-		StandardEvaluationContext ctx = new StandardEvaluationContext();
-		List<IndexAccessor> indexAccessors = ctx.getIndexAccessors();
-		assertThat(indexAccessors.size()).isEqualTo(0);
-		JsonIndexAccessor jsonIndexAccessor=new JsonIndexAccessor();
-		ctx.addIndexAccessor(jsonIndexAccessor);
-		assertThat(indexAccessors.size()).isEqualTo(1);
-		JsonIndexAccessor jsonIndexAccessor1=new JsonIndexAccessor();
-		ctx.addIndexAccessor(jsonIndexAccessor1);
-		assertThat(indexAccessors.size()).isEqualTo(2);
-		List copy=new ArrayList(indexAccessors);
-		assertThat(ctx.removeIndexAccessor(jsonIndexAccessor)).isTrue();
-		assertThat(ctx.removeIndexAccessor(jsonIndexAccessor)).isFalse();
-		assertThat(indexAccessors.size()).isEqualTo(1);
-		ctx.setIndexAccessors(copy);
-		assertThat(ctx.getIndexAccessors().size()).isEqualTo(2);
-	}
-
 	@Test
 	void accessingPropertyOfClass() {
 		Expression expression = parser.parseExpression("name");
@@ -248,24 +223,6 @@ class PropertyAccessTests extends AbstractExpressionTests {
 		assertThat(target.getName()).isEqualTo("p4");
 		assertThat(expr.getValue(context, target)).isEqualTo("p4");
 	}
-	@Test
-	public void indexReadWrite(){
-		StandardEvaluationContext context=new StandardEvaluationContext();
-		JsonIndexAccessor indexAccessor=new JsonIndexAccessor();
-		context.addIndexAccessor(indexAccessor);
-		ArrayNode arrayNode=indexAccessor.objectMapper.createArrayNode();
-		arrayNode.add(new TextNode("node0"));
-		arrayNode.add(new TextNode("node1"));
-		Expression expr=parser.parseExpression("[0]");
-		assertThat(new TextNode("node0").equals(expr.getValue(context,arrayNode))).isTrue();
-		expr.setValue(context,arrayNode,new TextNode("nodeUpdate"));
-		assertThat(new TextNode("nodeUpdate").equals(expr.getValue(context,arrayNode))).isTrue();
-		Expression expr1=parser.parseExpression("[1]");
-		assertThat(new TextNode("node1").equals(expr1.getValue(context,arrayNode))).isTrue();
-
-
-	}
-
 
 	@Test
 	void propertyReadWriteWithRootObject() {
@@ -406,67 +363,4 @@ class PropertyAccessTests extends AbstractExpressionTests {
 		}
 	}
 
-	private static class JsonIndexAccessor implements IndexAccessor {
-		ObjectMapper objectMapper=new ObjectMapper();
-		public class ArrayValueRef implements ValueRef {
-			ArrayNode arrayNode;
-			Integer index;
-
-			@Override
-			public TypedValue getValue() {
-				return new TypedValue(arrayNode.get(index));
-			}
-
-			@Override
-			public void setValue(Object newValue) {
-				arrayNode.set(index,objectMapper.convertValue(newValue, JsonNode.class));
-			}
-			public void setArrayNode(ArrayNode arrayNode){
-				this.arrayNode=arrayNode;
-			}
-
-			public void setIndex(Object index) {
-				if (index instanceof Integer) {
-					this.index = (Integer) index;
-				}
-			}
-
-			@Override
-			public boolean isWritable() {
-				return false;
-			}
-		}
-
-		@Override
-		public Class<?>[] getSpecificTargetClasses() {
-			return new Class[]{
-					ArrayNode.class
-			};
-		}
-
-		@Override
-		public boolean canRead(EvaluationContext context, Object target, Object index) throws AccessException {
-			return true;
-		}
-
-		@Override
-		public ValueRef read(EvaluationContext context, Object target, Object index) throws AccessException {
-			ArrayValueRef valueRef = new ArrayValueRef();
-			valueRef.setArrayNode((ArrayNode) target);
-			valueRef.setIndex(index);
-			return valueRef;
-		}
-
-		@Override
-		public boolean canWrite(EvaluationContext context, Object target, Object index) throws AccessException {
-			return true;
-		}
-
-		@Override
-		public void write(EvaluationContext context, Object target, Object index, Object newValue) throws AccessException {
-			ValueRef valueRef=read(context,target,index);
-			valueRef.setValue(newValue);
-		}
-	}
-
 }