Converting Exceptions Into HTTP Status Codes

An exception thrown in an "exceptional" resource:

@Path("exceptions")
public class ExceptionalResource {

    @GET
    public String dontCallMe() {
        throw new IllegalStateException("Do NOT call me");
    }

}

can be easily converted into a HTTP Status code using the ExceptionMapper:

import javax.ws.rs.core.Response;
import javax.ws.rs.ext.ExceptionMapper;
import javax.ws.rs.ext.Provider;


@Provider
public class IllegalStateExceptionMapper 
implements ExceptionMapper<IllegalStateException> {

    @Override
    public Response toResponse(IllegalStateException exception) {
        return Response.status(Response.Status.NOT_IMPLEMENTED).
                header("reason", exception.getMessage()).
                build();
    }

}

A curl -i http://localhost:8080/jaxrs-exceptionmapper/resources/exceptions outputs:

reason: Do NOT call me
Content-Language: 
Content-Type: text/html
Date: Wed, 20 Apr 2016 08:22:00 GMT
Connection: close
Content-Length: 1119

JPA OptimisticLockExceptions can be converted with the same mechanism.

Any questions left? See you at Java EE Workshops at Munich Airport, Terminal 2, particularly at: Effective Java EE 7 or at airhacks.io!