Custom ExceptionMapper not invoked when Hibernate rollback

[paukiatwee]

Using DW 0.8.0, Java 8

I have one custom exception mapper to handle hibernate exception:

import org.hibernate.exception.ConstraintViolationException;


@Provider
public class SQLConstraintViolationExceptionMapper implements ExceptionMapper<ConstraintViolationException> {
    ....
}

I registered the mapper https://github.com/paukiatwee/budgetapp/blob/master/src/main/java/io/budgetapp/BudgetApplication.java#L143

When org.hibernate.exception.ConstraintViolationException exception is thrown when foreign key violation occurred, SQLConstraintViolationExceptionMapper is no called.

You can reproduce the problem by running this integration test https://github.com/paukiatwee/budgetapp/blob/master/src/test/java/io/budgetapp/resource/CategoryResourceIT.java#L65

This might caused by https://github.com/dropwizard/dropwizard/blob/master/dropwizard-hibernate/src/main/java/io/dropwizard/hibernate/UnitOfWorkApplicationListener.java#L87 exception not handled by container.

Working fine for DW 0.7.0

[arteam]

I can confirm that issue.

Unfortunately, I can't give a solution now. The problem lies in the update to Jersey 2 in 0.8.0.
Seems to be UnitOfWorkApplicationListener doesn't work with exception mappers.

[arteam]

I've made another look and can give a workaround for you.

In 0.8.0 in UnitOfWorkApplicationListener we commit a Hibernate transaction after a request has been processed and response processing has been started. We don't have an event like BEFORE_RESOURCE_METHOD_FINISHED, so we are forced to make a commit (with possible errors) during response processing.

In the Jersey architecture at this stage exception mappers are not taken into account, but mappers that implement the interface ResponseErrorMapper are.
They are also not processed by default, so you need to enable this feature in configuration:

environment.jersey().property(ServerProperties.PROCESSING_RESPONSE_ERRORS_ENABLED, true);

After that you can refactor your exception mapper something like that:

@Provider
public class SQLConstraintViolationExceptionMapper implements ResponseErrorMapper {

    private static final Logger LOGGER = LoggerFactory.getLogger(SQLConstraintViolationExceptionMapper.class);

    @Override
    public Response toResponse(Throwable e) {
        return Response.status(Response.Status.BAD_REQUEST)
                .entity(Collections.singletonMap("errors",
                        Collections.singletonMap("message", getMessage((ConstraintViolationException) e))))
                .build();
    }

    private List<String> getMessage(ConstraintViolationException e) {

        LOGGER.error(e.getMessage(), e);

        // a hack to convert exception to friendly error message
        if ("fk_budgets_categories".equalsIgnoreCase(e.getConstraintName())) {
            return Collections.singletonList("Failed to delete category due to references to existing budget(s).");
        } else if ("fk_transactions_budgets".equalsIgnoreCase(e.getConstraintName())) {
            return Collections.singletonList("Failed to delete budget due to references to existing transaction(s).");
        }
        return Collections.singletonList(e.getMessage());
    }
}

Could you test this approach? If it works for you, I will add information about response error mappers
into the 0.8.0 migration guide.

[paukiatwee]

The issue is fixed after update based on your comment commit.

However, I think the proper way to fix this is to rethrow exception as org.glassfish.jersey.server.internal.process.MappableException as the doc mention:

 * A runtime exception that contains a cause, a checked or runtime exception,
 * that may be mapped to a {@link javax.ws.rs.core.Response} instance.
 * <p>
 * The runtime will catch such exceptions and attempt to map the cause
 * exception to a registered {@link javax.ws.rs.ext.ExceptionMapper} that
 * provides an appropriate {@link javax.ws.rs.core.Response} instance.

[arteam]

That actually seems like a better solution. Jersey will rethrow the original exception if it's unmapped and map to Response if it's mapped. Thanks for pointers.

I will try to create a PR for fixing that.