spring-projects/spring-framework · error · ConversionNotSupportedException

Failed to convert value of type '{}' to required type '{}'

Error message

Failed to convert value of type '{}' to required type '{}'

What it means

ConversionNotSupportedException raised by TypeConverterSupport when the delegate throws ConverterNotFoundException or IllegalStateException (see error 186). It signals that the conversion could not even be attempted because no converter/strategy exists. Carries the source value and required type; propertyName may be null.

Source

Thrown at spring-beans/src/main/java/org/springframework/beans/TypeConverterSupport.java:79

	}

	@Override
	public <T> @Nullable T convertIfNecessary(@Nullable Object value, @Nullable Class<T> requiredType,
			@Nullable TypeDescriptor typeDescriptor) throws TypeMismatchException {

		return convertIfNecessary(null, value, requiredType, typeDescriptor);
	}

	private <T> @Nullable T convertIfNecessary(@Nullable String propertyName, @Nullable Object value,
			@Nullable Class<T> requiredType, @Nullable TypeDescriptor typeDescriptor) throws TypeMismatchException {

		Assert.state(this.typeConverterDelegate != null, "No TypeConverterDelegate");
		try {
			return this.typeConverterDelegate.convertIfNecessary(
					propertyName, null, value, requiredType, typeDescriptor);
		}
		catch (ConverterNotFoundException | IllegalStateException ex) {
			throw new ConversionNotSupportedException(value, requiredType, ex);
		}
		catch (ConversionException | IllegalArgumentException ex) {
			throw new TypeMismatchException(value, requiredType, ex);
		}
	}

}

View on GitHub (pinned to 69bf83ad71)

Solutions

1. Register a Converter or PropertyEditor for the required type (same fixes as error 186).
2. Correct the target property type in the bean to a convertible type.
3. If the value is already correct, ensure ConversionService is actually wired into the BeanWrapper (setConversionService).

Example fix

// before
wrapper.setConversionService(null);
wrapper.setPropertyValue("when", "2023-01-01"); // target java.time.Instant, no converter

// after
DefaultConversionService cs = new DefaultConversionService();
cs.addConverter(String.class, Instant.class, Instant::parse);
wrapper.setConversionService(cs);
wrapper.setPropertyValue("when", "2023-01-01T00:00:00Z");

// Pre-check before converting
if (!conversionService.canConvert(TypeDescriptor.forObject(value), TypeDescriptor.valueOf(requiredType))) {
    throw new IllegalStateException("unsupported conversion; register a converter");
}

try {
    T result = converter.convertIfNecessary(value, requiredType, descriptor);
} catch (ConversionNotSupportedException ex) {
    // no converter exists — register one and retry, or fail with context
    log.warn("No converter for {} -> {}", value.getClass(), requiredType, ex);
    throw ex;
}

When it happens

Trigger: convertIfNecessary on a BeanWrapper / TypeConverterSupport for a (value, requiredType) pair with no registered Converter or PropertyEditor, so the delegate raises IllegalStateException and line 79 wraps it.

Common situations: @Value injection, @ConfigurationProperties binding, or manual BeanWrapper.setPropertyValue where the target type has no converter; Spring Boot relaxed binding encountering an unregistered custom type.

Related errors

• Cannot convert value of type '{}' to required type '{}'[ for
• Cannot convert value of type '{}' to required type '{}'[ for
• typeMismatch
• Nested property in path '{propertyName}' does not exist
• Failed properties: {propertyAccessExceptions}

AI-assisted analysis of spring-projects/spring-framework@69bf83ad71 (2026-08-09). Data as JSON: /api/errors/9e915964b51c7f11. Report an issue: GitHub.