quarkusio/quarkus · warning · UnsupportedOperationException

I cannot convert anything from JSON.

Error message

I cannot convert anything from JSON.

What it means

This UnsupportedOperationException is deliberately thrown by a custom Hibernate 6 FormatMapper (JSON) registered via @PersistenceUnitExtension("other") in a Quarkus integration test. The test PU intentionally has no working JSON conversion so that any attempt to read a JSON property from that persistence unit fails loudly. It is not a bug in a library but an intentional sentinel in the test codebase.

Source

Thrown at integration-tests/jpa-postgresql/src/main/java/io/quarkus/it/jpa/postgresql/otherpu/JsonFormatMapper.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.JsonFormat;
import io.quarkus.hibernate.orm.PersistenceUnitExtension;

@JsonFormat
@PersistenceUnitExtension("other")
public class JsonFormatMapper implements FormatMapper {

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

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

View on GitHub (pinned to e1c734241f)

Solutions

1. Use a real FormatMapper implementation (e.g. JacksonJsonFormatMapper) instead of this test stub
2. Remove the @PersistenceUnitExtension("other") JsonFormatMapper so Hibernate's default JSON mapper is used
3. If this is your own stub, implement fromString with an actual mapper (Jackson ObjectMapper) instead of throwing

Example fix

// before
public <T> T fromString(CharSequence charSequence, JavaType<T> javaType, WrapperOptions wrapperOptions) {
    throw new UnsupportedOperationException("I cannot convert anything from JSON.");
}
// after
public <T> T fromString(CharSequence charSequence, JavaType<T> javaType, WrapperOptions wrapperOptions) {
    return objectMapper.readValue(charSequence.toString(), objectMapper.constructType(javaType.getJavaType()));
}

boolean canRead = mapper != null && !(mapper instanceof JsonFormatMapper);

try {
    T value = mapper.fromString(json, javaType, options);
} catch (UnsupportedOperationException e) {
    throw new IllegalStateException("PU has no JSON read support: " + e.getMessage(), e);
}

When it happens

Trigger: Any code path that materializes an entity attribute mapped as JSON (FormatMapper#toString/fromString contract) for the 'other' persistence unit, causing Hibernate to call JsonFormatMapper.fromString to convert a DB JSON string into a Java object.

Common situations: Seen only when running the jpa-postgresql integration tests that use the secondary PU; a developer copying this mapper into a real application will hit it whenever Hibernate ORM needs JSON <-> Java conversion for Json/JsonJavaType attributes.

Related errors

• I cannot convert anything to JSON.
• flush failed for a different reason than expected.
• I cannot convert anything from XML.
• I cannot convert anything to XML.
• Json array ended without ]

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/153c82bc1abbcf85. Report an issue: GitHub.