spring-projects/spring-framework · error · IntrospectionException

Read method returns void: ${readMethod}

Error message

Read method returns void: ${readMethod}

What it means

IntrospectionException from PropertyDescriptorUtils.findPropertyType when the read method's return type is void. A getter must return the property value; a void return means there is no property type, so descriptor construction is impossible.

Source

Thrown at spring-beans/src/main/java/org/springframework/beans/PropertyDescriptorUtils.java:159

		target.setBound(source.isBound());
		target.setConstrained(source.isConstrained());
	}

	/**
	 * See {@link java.beans.PropertyDescriptor#findPropertyType}.
	 */
	public static @Nullable Class<?> findPropertyType(@Nullable Method readMethod, @Nullable Method writeMethod)
			throws IntrospectionException {

		Class<?> propertyType = null;

		if (readMethod != null) {
			if (readMethod.getParameterCount() != 0) {
				throw new IntrospectionException("Bad read method arg count: " + readMethod);
			}
			propertyType = readMethod.getReturnType();
			if (propertyType == void.class) {
				throw new IntrospectionException("Read method returns void: " + readMethod);
			}
		}

		if (writeMethod != null) {
			Class<?>[] params = writeMethod.getParameterTypes();
			if (params.length != 1) {
				throw new IntrospectionException("Bad write method arg count: " + writeMethod);
			}
			if (propertyType != null) {
				if (propertyType.isAssignableFrom(params[0])) {
					// Write method's property type potentially more specific
					propertyType = params[0];
				}
				else if (params[0].isAssignableFrom(propertyType)) {
					// Proceed with read method's property type
				}
				else {
					throw new IntrospectionException(

View on GitHub (pinned to e8729d0438)

Solutions

1. Give the method a non-void return type matching the field it exposes.
2. If the method is a command not an accessor, rename it (e.g. fetchFoo(), loadFoo()) so it isn't treated as a getter.
3. Drop it from the PropertyDescriptor construction.

Example fix

// before
public void getItems() { /* no-op */ }

// after
public List<String> getItems() { return items; }

static void assertReadMethodReturnsValue(Method readMethod) {
    if (readMethod.getReturnType() == void.class) {
        throw new IllegalArgumentException("Read method must not return void: " + readMethod);
    }
}

static boolean returnsValue(Method m) {
    return m != null && m.getReturnType() != void.class;
}

try {
    return new PropertyDescriptor(name, readMethod, writeMethod);
} catch (java.beans.IntrospectionException ex) {
    if (ex.getMessage().startsWith("Read method returns void")) {
        log.error("Getter {} returns void; cannot be a property read method", readMethod);
    }
    throw ex;
}

When it happens

Trigger: Registering a getFoo() method that returns void as the readMethod of a PropertyDescriptor; rare in normal code, usually a coding error or generated bytecode where 'get' is used as a verb without a return.

Common situations: Hand-written getFoo() void methods mistaken for accessors; generated stubs where the getter body was left empty and the return type is void; legacy code where 'get' is a command rather than an accessor.

Related errors

• Bad read method arg count: ${readMethod}
• Bean property '{propertyName}' is not readable or has an inv
• Bad write method arg count: ${writeMethod}
• Type mismatch between read and write methods: ${readMethod}
• Bad indexed read method arg count: ${indexedReadMethod}

AI-assisted analysis of spring-projects/spring-framework@e8729d0438 (2026-08-04). Data as JSON: /data/errors/c7fd173eab493bed.json. Report an issue: GitHub.