quarkusio/quarkus · error · UnsupportedOperationException

I cannot convert anything from XML.

Error message

I cannot convert anything from XML.

What it means

XmlFormatMapper.fromString unconditionally throws UnsupportedOperationException('I cannot convert anything from XML.'). This mapper is a deliberately degenerate FormatMapper registered via @PersistenceUnitExtension("other") with @XmlFormat for the 'other' persistence unit; it is used by the integration test to prove that Hibernate calls the custom mapper. Any code path that deserializes an XML-format column value from that persistence unit will always fail with this exception.

Source

Thrown at integration-tests/jpa-postgresql-withxml/src/main/java/io/quarkus/it/jpa/postgresql/otherpu/XmlFormatMapper.java:16

package io.quarkus.it.jpa.postgresql.otherpu;

import org.hibernate.type.descriptor.WrapperOptions;
import org.hibernate.type.descriptor.java.JavaType;
import org.hibernate.type.format.FormatMapper;

import io.quarkus.hibernate.orm.PersistenceUnitExtension;
import io.quarkus.hibernate.orm.XmlFormat;

@XmlFormat
@PersistenceUnitExtension("other")
public class XmlFormatMapper implements FormatMapper {

    @Override
    public <T> T fromString(CharSequence charSequence, JavaType<T> javaType, WrapperOptions wrapperOptions) {
        throw new UnsupportedOperationException("I cannot convert anything from XML.");
    }

    @Override
    public <T> String toString(T value, JavaType<T> javaType, WrapperOptions wrapperOptions) {
        throw new UnsupportedOperationException("I cannot convert anything to XML.");
    }
}

View on GitHub (pinned to e1c734241f)

Solutions

1. Do not use XmlFormatMapper in production code — it is a test-only mapper that intentionally fails
2. Implement fromString properly in your custom FormatMapper (e.g. parse the CharSequence with a real XML/JSON parser)
3. Check the @PersistenceUnitExtension qualifier so the real mapper, not the throwing test one, is bound to your persistence unit
4. If reading should be supported but writing not, implement fromString and keep throwing only in toString

Example fix

// before
@Override
public <T> T fromString(CharSequence charSequence, JavaType<T> javaType, WrapperOptions wrapperOptions) {
    throw new UnsupportedOperationException("I cannot convert anything from XML.");
}
// after
@Override
public <T> T fromString(CharSequence charSequence, JavaType<T> javaType, WrapperOptions wrapperOptions) {
    return (T) xmlMapper.readValue(charSequence.toString(), javaType.getJavaClass());
}

// Check which FormatMapper is bound to your persistence unit before relying on XML reads
if (formatMapper instanceof XmlFormatMapper) {
    throw new IllegalStateException("Test-only XmlFormatMapper is active; XML reads are not supported");
}

static boolean supportsReading(FormatMapper mapper) {
    return !(mapper instanceof XmlFormatMapper);
}

try {
    EntityWithXmlOtherPU e = em.find(EntityWithXmlOtherPU.class, id);
} catch (UnsupportedOperationException e) {
    if (e.getMessage() != null && e.getMessage().contains("I cannot convert anything from XML")) {
        // fall back to a working mapper or raw column read
    } else {
        throw e;
    }
}

When it happens

Trigger: Reading (deserializing) an entity property that Hibernate maps with the XML format mapper from the 'other' persistence unit — e.g. loading an EntityWithXmlOtherPU row whose property must be converted from the stored string back to Java via fromString.

Common situations: Queries that select entities with @JdbcTypeCode(SqlTypes.JSON)-style XML-mapped properties from the 'other' PU; accidentally wiring this test mapper (or copying it) into a real application PU where XML conversion should actually work.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• I cannot convert anything to XML.
• This isn't used for schema generation - see SessionFactoryOb
• This method is not available at runtime in Quarkus
• I cannot convert anything from JSON.
• I cannot convert anything to JSON.

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/cb2685ba70052046. Report an issue: GitHub.