Even though the Java API for RESTful Web Services (JAX-RS) runtime environment includes several entity providers for handling serialization from and deserialization to Java types, it does not support all possible media types. You can develop a custom entity provider to handle binding Java types to message bodies.
If your JAX-RS web application requires that additional Java types or media types are supported beyond what the JAX-RS APIs support, you can add a custom entity provider to the application. Any custom-defined entity provider takes precedence over the entity providers that are included in the JAX-RS runtime environment. Unlike resources, providers are always singleton beans.
You have developed and deployed a JAX-RS web application that contains a custom entity provider.