The POJO to JSON mapping uses a mechanism of the entity provider of the JAX-RS specifications. The exceptions thrown during the POJO to JSON mapping, therefore, is handled in the same way as the exceptions thrown during any other mapping. For details on how exceptions are handled during mapping, see 17.1.3 Return value and for mapping on servers and for mapping on clients, see 25.15.1 Combination of Java types and MIME media types available for an HTTP request entity.