JAX-RS using exception mappers

Question

I have read that I can create an implementation of javax.ws.rs.ext.ExceptionMapper that will map a thrown application exception to a Response object.

I've created a simple example which throws an exception if the phone length is greater than 20 characters when persisting the object. I am expecting the exception to be mapped to an HTTP 400 (Bad Request) response; however, I am receiving an HTTP 500 (Internal Server Error) with the following exception:

java.lang.ClassCastException: com.example.exception.InvalidDataException cannot be cast to java.lang.Error

What am I missing? Any advice is greatly appreciated.

Exception mapper:

@Provider
public class InvalidDataMapper implements ExceptionMapper<InvalidDataException> {

    @Override
    public Response toResponse(InvalidDataException arg0) {
        return Response.status(Response.Status.BAD_REQUEST).build();
    }

}

Exception class:

public class InvalidDataException extends Exception {

    private static final long serialVersionUID = 1L;

    public InvalidDataException(String message) {
        super(message);
    }

    ...

}

Entity class:

@Entity
@Table(name="PERSON")
@XmlAccessorType(XmlAccessType.FIELD)
@XmlRootElement
public class Person {

    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name="ID")
    private Long id;

    @Column(name="NAME")
    private String name;

    @Column(name="PHONE")
    private String phone;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPhone() {
        return phone;
    }

    public void setPhone(String phone) {
        this.phone = phone;
    }   

    @PrePersist
    public void validate() throws InvalidDataException {
        if (phone != null) {
            if (phone.length() > 20) {
                throw new InvalidDataException("Phone number too long: " + phone);
            }
        }       
    }
}

Service:

@Path("persons/")
@Produces(MediaType.APPLICATION_XML)
@Consumes(MediaType.APPLICATION_XML)
@Stateless
public class PersonResource {

    @Context
    private UriInfo uriInfo;

    @PersistenceContext(name="simple")
    private EntityManager em;

    @POST
    public Response createPerson(JAXBElement<Person> personJaxb) {
        Person person = personJaxb.getValue();
        em.persist(person);
        em.flush();
        URI personUri = uriInfo.getAbsolutePathBuilder().
        path(person.getId().toString()).build();
        return Response.created(personUri).build();  
    }

}

Solution

Is InvalidDataException getting wrapped in a PersistenceException? Maybe you could do something like the following:

@Provider 
public class PersistenceMapper implements ExceptionMapper<PersistenceException> { 

    @Override 
    public Response toResponse(PersistenceException arg0) { 
        if(arg0.getCause() instanceof InvalidDataException) {
           return Response.status(Response.Status.BAD_REQUEST).build(); 
        } else {
           ...
        }
    } 

} 

Comments

[Jordan Allan]

Thank-you Blaise, that worked. Why must I wrap InvalidDataException in a PersistenceException though? According to one of the books I have, it says the JAX-RS runtime will handle any thrown exception if an exception mapper is registered. In my case, I registered an exception mapper for InvalidDataException...

[bdoughan]

The JPA implementation is going to catch InvalidDataException and wrap it in PersistenceException. Then your JAX-RS implementation is going to get a PersistenceException. This is why you need to unwrap it.

[bdoughan]

Also see stackoverflow.com/questions/3249495/…

[Jordan Allan]

Makes perfect sense now. Thanks!

[Catalin Morosan]

What should go into the else statement? If there is a different exception, I want the jax-rs implementation to handle it with its default behavior.

[bdoughan]

@kaciula - What goes into the else statement depends on your application. Ultimately you could build different types of Response objects based on the different types of nested exceptions.

[ksl]

@BlaiseDoughan Why does the InvalidDataException get wrapped in a PersistenceException?