spring-projects/spring-framework · error · InvalidPropertyException

Cannot get element with index

Error message

Cannot get element with index {index} from Collection of size {coll.size()}, accessed using property path '{propertyName}'

What it means

Thrown by getPropertyValue in the Collection branch (Set/Collection indexed read) when the requested index is < 0 or >= coll.size(). Sets and generic Collections have no positional access, so Spring iterates; before iterating it bounds-checks the size against the index for a clear error.

Solutions

Change the field to a List if positional access is required (List preserves insertion order and supports get).
Bounds-check the index against collection.size() before issuing the indexed read.
If the Set is intentional, expose iteration rather than positional access in the API.
Reject/normalize out-of-range indices in the controller or validator.

Example fix

// before
private Set<String> tags = new HashSet<>(); // size 1
wrapper.getPropertyValue("tags[3]");

// after
private List<String> tags = new ArrayList<>();
wrapper.getPropertyValue("tags[3]"); // with size >= 4

Defensive patterns

Strategy: validation

Validate before calling

BeanWrapper w = new BeanWrapperImpl(bean);
Object coll = w.getPropertyValue("tags");
if (coll instanceof Collection<?> c && (idx < 0 || idx >= c.size())) {
    throw new IndexOutOfBoundsException("set has " + c.size() + " elements; requested " + idx);
}
w.getPropertyValue("tags[" + idx + "]");

Type guard

static boolean indexInCollection(Object coll, int idx) {
    return coll instanceof Collection<?> c && idx >= 0 && idx < c.size();
}

Try / catch

try {
    return wrapper.getPropertyValue("tags[" + idx + "]");
} catch (InvalidPropertyException ex) {
    if (ex.getMessage().contains("from Collection of size")) return null; // out of range
    throw ex;
}

Prevention

Use a List instead of a Set whenever positional access is required.
Bounds-check indices against collection.size() before indexed reads.
Document that Set ordering is iteration-defined, not index-stable.

When it happens

Trigger: getPropertyValue("set[3]") on a Set/Collection of size <= 3 (or negative index).

Common situations: Binding/reading indexed positions on a Set (order may be undefined); client expecting list semantics on a Set field; index derived from request params that exceeds collection size.

Related errors

AI-assisted analysis of spring-projects/spring-framework@69bf83ad71 (2026-08-09). Data as JSON: /api/errors/db295b3b51b14fc3. Report an issue: GitHub.

Appendix: source

Thrown at spring-beans/src/main/java/org/springframework/beans/AbstractNestablePropertyAccessor.java:650

					else if (value instanceof List list) {
						int index = Integer.parseInt(key);
						growCollectionIfNecessary(list, index, indexedPropertyName.toString(), ph, i + 1);
						value = list.get(index);
					}
					else if (value instanceof Map map) {
						Class<?> mapKeyType = ph.getResolvableType().getNested(i + 1).asMap().resolveGeneric(0);
						// IMPORTANT: Do not pass full property name in here - property editors
						// must not kick in for map keys but rather only for map values.
						TypeDescriptor typeDescriptor = TypeDescriptor.valueOf(mapKeyType);
						Object convertedMapKey = convertIfNecessary(null, null, key, mapKeyType, typeDescriptor);
						value = map.get(convertedMapKey);
					}
					else if (value instanceof Iterable iterable) {
						// Apply index to Iterator in case of a Set/Collection/Iterable.
						int index = Integer.parseInt(key);
						if (value instanceof Collection<?> coll) {
							if (index < 0 || index >= coll.size()) {
								throw new InvalidPropertyException(getRootClass(), this.nestedPath + propertyName,
										"Cannot get element with index " + index + " from Collection of size " +
												coll.size() + ", accessed using property path '" + propertyName + "'");
							}
						}
						Iterator<Object> it = iterable.iterator();
						boolean found = false;
						int currIndex = 0;
						for (; it.hasNext(); currIndex++) {
							Object elem = it.next();
							if (currIndex == index) {
								value = elem;
								found = true;
								break;
							}
						}
						if (!found) {
							throw new InvalidPropertyException(getRootClass(), this.nestedPath + propertyName,
									"Cannot get element with index " + index + " from Iterable of size " +

View on GitHub (pinned to 69bf83ad71)