Add support for making MapAccessor read-only

spring-context/src/main/java/org/springframework/context/expression/MapAccessor.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.
@@ -33,10 +33,30 @@
  *
  * @author Juergen Hoeller
  * @author Andy Clement
+ * @author Yanming Zhou
  * @since 3.0
  */
 public class MapAccessor implements CompilablePropertyAccessor {
 
+	private final boolean allowWrite;
+
+	/**
+	 * Create a new map accessor for reading as well as writing.
+	 * @see #MapAccessor(boolean)
+	 */
+	public MapAccessor() {
+		this(true);
+	}
+
+	/**
+	 * Create a new map accessor for reading and possibly also writing.
+	 * @param allowWrite whether to allow write operations on a target instance
+	 * @see #canWrite
+	 */
+	public MapAccessor(boolean allowWrite) {
+		this.allowWrite = allowWrite;
+	}
+
 	@Override
 	public Class<?>[] getSpecificTargetClasses() {
 		return new Class<?>[] {Map.class};
@@ -60,7 +80,7 @@ public TypedValue read(EvaluationContext context, @Nullable Object target, Strin
 
 	@Override
 	public boolean canWrite(EvaluationContext context, @Nullable Object target, String name) throws AccessException {
-		return true;
+		return this.allowWrite;
 	}
 
 	@Override

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

@@ -32,6 +32,7 @@
  * Tests for {@link MapAccessor}.
  *
  * @author Andy Clement
+ * @author Yanming Zhou
  */
 class MapAccessorTests {
 
@@ -80,6 +81,16 @@ void mapAccessorCompilable() {
 		assertThat(ex.getValue(sec,testMap)).isEqualTo("bar2");
 	}
 
+	@Test
+	void mapAccessorNotWritable() {
+		Map<String, Object> testMap = getSimpleTestMap();
+		StandardEvaluationContext sec = new StandardEvaluationContext();
+		sec.addPropertyAccessor(new MapAccessor(false));
+		SpelExpressionParser sep = new SpelExpressionParser();
+		Expression ex = sep.parseExpression("foo");
+		assertThat(ex.isWritable(sec, testMap)).isFalse();
+	}
+
 	public static class MapGetter {
 		Map<String,Object> map = new HashMap<>();