SPR-6984: auto grow collections on write through indexer

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

@@ -61,7 +61,6 @@ public class Indexer extends SpelNodeImpl {
 		super(pos, expr);
 	}
 
-	@SuppressWarnings("unchecked")
 	@Override
 	public TypedValue getValueInternal(ExpressionState state) throws EvaluationException {
 		TypedValue context = state.getActiveContextObject();
@@ -119,28 +118,7 @@ public class Indexer extends SpelNodeImpl {
 			} else if (targetObject instanceof Collection) {
 				Collection c = (Collection) targetObject;
 				if (idx >= c.size()) {
-					if (state.getConfiguration().isAutoGrowCollections()) {
+					if (!growCollection(state, targetObjectTypeDescriptor.getElementType(), idx, c)) {
-						// Grow the collection
-						Object newCollectionElement = null;
-						try {
-							int newElements = idx-c.size();
-							Class elementClass = targetObjectTypeDescriptor.getElementType();
-							if (elementClass == null) {
-								throw new SpelEvaluationException(getStartPosition(), SpelMessage.UNABLE_TO_GROW_COLLECTION_UNKNOWN_ELEMENT_TYPE);	
-							}
-							while (newElements>0) {
-								c.add(elementClass.newInstance());
-								newElements--;
-							}
-							newCollectionElement = targetObjectTypeDescriptor.getElementType().newInstance();
-						}
-						catch (Exception ex) {
-							throw new SpelEvaluationException(getStartPosition(), ex, SpelMessage.UNABLE_TO_GROW_COLLECTION);
-						}
-						c.add(newCollectionElement);
-						return new TypedValue(newCollectionElement,TypeDescriptor.valueOf(targetObjectTypeDescriptor.getElementType()));
-					}
-					else {
 						throw new SpelEvaluationException(getStartPosition(),SpelMessage.COLLECTION_INDEX_OUT_OF_BOUNDS, c.size(), idx);
 					}
 				}
@@ -234,8 +212,10 @@ public class Indexer extends SpelNodeImpl {
 			int idx = (Integer)state.convertValue(index, TypeDescriptor.valueOf(Integer.class));
 			Collection c = (Collection) targetObject;
 			if (idx >= c.size()) {
+				if (!growCollection(state, targetObjectTypeDescriptor.getElementType(), idx, c)) {
 					throw new SpelEvaluationException(getStartPosition(),SpelMessage.COLLECTION_INDEX_OUT_OF_BOUNDS, c.size(), idx);
 				}
+			}
 			if (targetObject instanceof List) {
 				List list = (List)targetObject;
 				Object possiblyConvertedValue = state.convertValue(newValue,TypeDescriptor.valueOf(targetObjectTypeDescriptor.getElementType()));
@@ -282,6 +262,40 @@ public class Indexer extends SpelNodeImpl {
 		throw new SpelEvaluationException(getStartPosition(),SpelMessage.INDEXING_NOT_SUPPORTED_FOR_TYPE, targetObjectTypeDescriptor.asString());
 	}
 	
+	/**
+	 * Attempt to grow the specified collection so that the specified index is valid.
+	 * 
+	 * @param state the expression state
+	 * @param elementType the type of the elements in the collection
+	 * @param index the index into the collection that needs to be valid
+	 * @param collection the collection to grow with elements
+	 * @return true if collection growing succeeded, otherwise false
+	 */
+	@SuppressWarnings("unchecked")
+	private boolean growCollection(ExpressionState state, Class<?> elementType, int index,
+			Collection collection) {
+		if (state.getConfiguration().isAutoGrowCollections()) {
+			Object newCollectionElement = null;
+			try {
+				int newElements = index-collection.size();
+				if (elementType == null) {
+					throw new SpelEvaluationException(getStartPosition(), SpelMessage.UNABLE_TO_GROW_COLLECTION_UNKNOWN_ELEMENT_TYPE);	
+				}
+				while (newElements>0) {
+					collection.add(elementType.newInstance());
+					newElements--;
+				}
+				newCollectionElement = elementType.newInstance();
+			}
+			catch (Exception ex) {
+				throw new SpelEvaluationException(getStartPosition(), ex, SpelMessage.UNABLE_TO_GROW_COLLECTION);
+			}
+			collection.add(newCollectionElement);
+			return true;
+		}
+		return false;
+	}
+	
 	@Override
 	public String toStringAST() {
 		StringBuilder sb = new StringBuilder();

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

@@ -31,6 +31,7 @@ import org.springframework.expression.spel.standard.SpelExpression;
 import org.springframework.expression.spel.standard.SpelExpressionParser;
 import org.springframework.expression.spel.support.StandardEvaluationContext;
 import org.springframework.expression.spel.support.StandardTypeLocator;
+import org.springframework.expression.spel.testresources.TestPerson;
 
 /**
  * Tests the evaluation of real expressions in a real context.
@@ -522,4 +523,31 @@ public class EvaluationTests extends ExpressionTestCase {
 		Assert.assertEquals(String.class,stringClass);
 	} 
 	 
+	/**
+	 * SPR-6984: attempting to index a collection on write using an index that doesn't currently exist in the collection (address.crossStreets[0] below)
+	 */
+	@Test
+	public void initializingCollectionElementsOnWrite() throws Exception {
+		TestPerson person = new TestPerson();
+		EvaluationContext context = new StandardEvaluationContext(person);
+		SpelParserConfiguration config = new SpelParserConfiguration(true, true);
+		ExpressionParser parser = new SpelExpressionParser(config);
+		Expression expression = parser.parseExpression("name");
+		expression.setValue(context, "Oleg");
+		Assert.assertEquals("Oleg",person.getName());
+
+		expression = parser.parseExpression("address.street");
+		expression.setValue(context, "123 High St");
+		Assert.assertEquals("123 High St",person.getAddress().getStreet());
+		
+		expression = parser.parseExpression("address.crossStreets[0]");
+		expression.setValue(context, "Blah");
+		Assert.assertEquals("Blah",person.getAddress().getCrossStreets().get(0));
+		
+		expression = parser.parseExpression("address.crossStreets[3]");
+		expression.setValue(context, "Wibble");
+		Assert.assertEquals("Blah",person.getAddress().getCrossStreets().get(0));
+		Assert.assertEquals("Wibble",person.getAddress().getCrossStreets().get(3));
+	}
+	
 }

org.springframework.expression/src/test/java/org/springframework/expression/spel/testresources/TestAddress.java

@@ -0,0 +1,21 @@
+package org.springframework.expression.spel.testresources;
+
+import java.util.List;
+
+public class TestAddress{
+		private String street;
+		private List<String> crossStreets;
+		
+		public String getStreet() {
+			return street;
+		}
+		public void setStreet(String street) {
+			this.street = street;
+		}
+		public List<String> getCrossStreets() {
+			return crossStreets;
+		}
+		public void setCrossStreets(List<String> crossStreets) {
+			this.crossStreets = crossStreets;
+		}
+	}

org.springframework.expression/src/test/java/org/springframework/expression/spel/testresources/TestPerson.java

@@ -0,0 +1,19 @@
+package org.springframework.expression.spel.testresources;
+
+public class TestPerson {
+		private String name;
+		private TestAddress address;
+		
+		public String getName() {
+			return name;
+		}
+		public void setName(String name) {
+			this.name = name;
+		}
+		public TestAddress getAddress() {
+			return address;
+		}
+		public void setAddress(TestAddress address) {
+			this.address = address;
+		}
+	}