spring-projects/spring-framework · error · IntrospectionException

Bad indexed read method arg count

Error message

Bad indexed read method arg count: {}

What it means

Thrown as java.beans.IntrospectionException by PropertyDescriptorUtils.findIndexedPropertyType when an indexed read method does not have exactly one parameter. Indexed getters must take exactly one (the int index) parameter.

Solutions

1. Make the indexed read method take exactly one parameter (the int index): Type getXxx(int i).
2. If the property is not indexed, do not register the method as an indexed accessor.
3. Correct or regenerate the offending class.

Example fix

// before
public Item getItem(); // wrong arity for indexed getter

// after
public Item getItem(int i);

if (indexedReadMethod != null && indexedReadMethod.getParameterCount() != 1) {
    throw new IllegalArgumentException("indexed getter must take 1 arg: " + indexedReadMethod);
}

static boolean validIndexedReadMethod(Method m) {
    return m != null && m.getParameterCount() == 1 && m.getParameterTypes()[0] == int.class
        && m.getReturnType() != void.class;
}

When it happens

Trigger: findIndexedPropertyType is called with an indexedReadMethod whose parameter count != 1 - e.g. an indexed getter taking 0 args (degenerate simple getter) or 2+ args.

Common situations: A method intended as an indexed getter (getXxx(int)) that has wrong arity, misregistration of a plain getter as indexed, or generated classes with malformed indexed accessors.

Related errors

• Bad indexed write method arg count
• Indexed read method returns void
• Non int index to indexed read method
• Bad read method arg count
• Bad write method arg count

AI-assisted analysis of spring-projects/spring-framework@69bf83ad71 (2026-08-09). Data as JSON: /api/errors/4da3b050af01f938. Report an issue: GitHub.

Appendix: source

Thrown at spring-beans/src/main/java/org/springframework/beans/PropertyDescriptorUtils.java:200

				propertyType = params[0];
			}
		}

		return propertyType;
	}

	/**
	 * See {@link java.beans.IndexedPropertyDescriptor#findIndexedPropertyType}.
	 */
	public static @Nullable Class<?> findIndexedPropertyType(String name, @Nullable Class<?> propertyType,
			@Nullable Method indexedReadMethod, @Nullable Method indexedWriteMethod) throws IntrospectionException {

		Class<?> indexedPropertyType = null;

		if (indexedReadMethod != null) {
			Class<?>[] params = indexedReadMethod.getParameterTypes();
			if (params.length != 1) {
				throw new IntrospectionException("Bad indexed read method arg count: " + indexedReadMethod);
			}
			if (params[0] != int.class) {
				throw new IntrospectionException("Non int index to indexed read method: " + indexedReadMethod);
			}
			indexedPropertyType = indexedReadMethod.getReturnType();
			if (indexedPropertyType == void.class) {
				throw new IntrospectionException("Indexed read method returns void: " + indexedReadMethod);
			}
		}

		if (indexedWriteMethod != null) {
			Class<?>[] params = indexedWriteMethod.getParameterTypes();
			if (params.length != 2) {
				throw new IntrospectionException("Bad indexed write method arg count: " + indexedWriteMethod);
			}
			if (params[0] != int.class) {
				throw new IntrospectionException("Non int index to indexed write method: " + indexedWriteMethod);
			}

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