quarkusio/quarkus · error · InternalServerErrorException

Could not find MessageBodyWriter for

Error message

Could not find MessageBodyWriter for 

What it means

Runtime serialization failure in FixedEntityWriterArray.write: none of the pre-selected MessageBodyWriter instances for the fixed writer array can write the response entity's Java type/media type combination. The entity class that failed to find a writer follows the message; typically a missing writer dependency (e.g. no REST Jackson for the type) or an unserializable return type on the endpoint.

Source

Thrown at independent-projects/resteasy-reactive/server/runtime/src/main/java/org/jboss/resteasy/reactive/server/core/serialization/FixedEntityWriterArray.java:35

public class FixedEntityWriterArray implements EntityWriter {

    private final MessageBodyWriter[] writers;
    private final ServerSerialisers serialisers;

    public FixedEntityWriterArray(MessageBodyWriter[] writers, ServerSerialisers serialisers) {
        this.writers = writers;
        this.serialisers = serialisers;
    }

    @Override
    public void write(ResteasyReactiveRequestContext context, Object entity) throws IOException {
        for (int i = 0; i < writers.length; ++i) {
            MessageBodyWriter writer = writers[i];
            if (ServerSerialisers.invokeWriter(context, entity, writer, serialisers)) {
                return;
            }
        }
        throw new InternalServerErrorException("Could not find MessageBodyWriter for " + entity.getClass(),
                Response.serverError().build());
    }
}

View on GitHub (pinned to e1c734241f)

Solutions

1. Add quarkus-rest-jackson/quarkus-rest-jsonb so a JSON writer is in the candidate set.
2. Narrow or correct the declared return type so build-time selection includes the right writer.
3. Verify @Produces media types match a registered writer for the entity.
4. Annotate the entity with @RegisterForReflection and rebuild (needed for native).

Example fix

// before
@GET @Produces({"application/json"})
public Object get() { return List.of(new Dto()); } // no writer matches
// after
@GET @Produces(MediaType.APPLICATION_JSON)
public List<Dto> get() { return List.of(new Dto()); }

try {
    return invocation.invoke();
} catch (InternalServerErrorException e) {
    if (e.getMessage() != null && e.getMessage().contains("Could not find MessageBodyWriter")) {
        throw new IllegalStateException("No writer in build-time candidate set for " + entityClass, e);
    }
    throw e;
}

When it happens

Trigger: A resource with multiple possible return/produces combinations (e.g. @Produces({JSON, TEXT})) returns an entity class that none of the preselected writers can handle.

Common situations: Returning a type outside the set anticipated at build time (Object, exotic collections); missing JSON extension so no writer in the array handles POJOs; runtime class differs from declared type.

Related errors

• Could not find MessageBodyWriter for
• Could not find MessageBodyWriter for
• Could not find MessageBodyWriter for
• Failed to serialize content of type
• Could not find MessageBodyWriter for ${entityClass}

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/999e2bb26ba95a1b. Report an issue: GitHub.