hibernate/hibernate-orm · error · UnsupportedOperationException

Unsupportd target type

Error message

Unsupportd target type 

What it means

FormatMapper (selected via AvailableSettings.JSON_FORMAT_MAPPER / XML_FORMAT_MAPPER) can stream aggregates directly into a target object (e.g. Oracle's OracleJsonGenerator for binary OSON) via writeToTarget, with supportsTargetType advertising capability. The default implementation throws UnsupportedOperationException 'Unsupportd target type ' + target.getClass() (note the 'Unsupportd' typo in Hibernate's message) whenever the configured mapper does not override it for that target type.

Source

Thrown at hibernate-core/src/main/java/org/hibernate/type/format/FormatMapper.java:66

	 * Checks that this mapper supports a type as a source type.
	 * @param sourceType the source type
	 * @return <code>true</code> if the type is supported, false otherwise.
	 */
	default boolean supportsSourceType(Class<?> sourceType) {
		return false;
	};

	/**
	 * Checks that this mapper supports a type as a target type.
	 * @param targetType the target type
	 * @return <code>true</code> if the type is supported, false otherwise.
	 */
	default boolean supportsTargetType(Class<?> targetType) {
		return false;
	}

	default <T> void writeToTarget(T value, JavaType<T> javaType, Object target, WrapperOptions options) throws IOException {
		throw new UnsupportedOperationException( "Unsupportd target type " + target.getClass() );
	};

	default <T> T readFromSource(JavaType<T> javaType, Object source, WrapperOptions options) throws IOException {
		throw new UnsupportedOperationException( "Unsupportd source type " + source.getClass() );
	};
}

View on GitHub (pinned to fad1729dce)

Solutions

1. Override writeToTarget (and supportsTargetType to advertise it) in your FormatMapper for the targets Hibernate passes
2. Use the built-in mapper matching the target type - Jackson mapper for String/Writer, the Oracle OSON mapper for OracleJsonGenerator
3. Keep the hibernate.type.json_format_mapper setting consistent with the dialect's storage format

Example fix

// before - custom mapper without target support
public class MyMapper implements FormatMapper {
    // only fromString/toString implemented -> 'Unsupportd target type'
}

// after
public class MyMapper implements FormatMapper {
    @Override public boolean supportsTargetType(Class<?> t) {
        return OracleJsonGenerator.class.isAssignableFrom(t);
    }
    @Override public <T> void writeToTarget(T value, JavaType<T> javaType, Object target, WrapperOptions options) throws IOException {
        // write through a JsonDocumentWriter backed by (OracleJsonGenerator) target
    }
    // ...
}

FormatMapper mapper = sessionFactory.getSessionFactoryOptions().getJsonFormatMapper();
if (!mapper.supportsTargetType(OracleJsonGenerator.class)) {
    // do not stream; fall back to the string API
    String json = mapper.toString(value, javaType, options);
}

When it happens

Trigger: The ORM serializes a JSON aggregate to a non-String target while the configured FormatMapper only supports CharSequence output - e.g. the Oracle OSON path handing an OracleJsonGenerator to a Jackson-based custom mapper, or your own FormatMapper that implemented only toString/fromString.

Common situations: Registering a custom FormatMapper (hibernate.type.json_format_mapper) written before the writeToTarget API existed; Oracle JSON binary storage combined with a third-party mapper; version upgrades that started calling writeToTarget for aggregate writes.

Related errors

• Unsupportd source type
• No more item in JSON document
• Unknown OSON event: {}
• no object key available
• Unsupported numeric type: {}

AI-assisted analysis of hibernate/hibernate-orm@fad1729dce (2026-08-22). Data as JSON: /api/errors/2a6b388f5a789ff0. Report an issue: GitHub.