Server Responses and Exception Handling - RESTful Java with JAX-RS 2.0 - page 109

list . add ( new new Customer (...));

GenericEntity entity = new GenericEntity < List < Customer >>( list ){};
return

return Response . ok ( entity ). build ();

}

The GenericEntity class is a Java generic template. What you do here is create an anonym-
ous class that extends GenericEntity , initializing the GenericEntity 's template with the
generic type you're using. If this looks a bit magical, it is. The creators of Java generics
made things a bit difficult, so we're stuck with this solution.

Exception Handling

Errors can be reported to a client either by creating and returning the appropriate Response
object or by throwing an exception. Application code is allowed to throw any checked
(classes extending java.lang.Exception ) or unchecked (classes extending
java.lang.RuntimeException ) exceptions they want. Thrown exceptions are handled by
the JAX-RS runtime if you have registered an exception mapper. Exception mappers can
convert an exception to an HTTP response. If the thrown exception is not handled by a map-
per, it is propagated and handled by the container (i.e., servlet) JAX-RS is running within.
JAX-RS also provides the javax.ws.rs.WebApplicationException . This can be thrown
by application code and automatically processed by JAX-RS without having to write an ex-
plicit mapper. Let's look at how to use the WebApplicationException first. We'll then ex-
amine how to write your own specific exception mappers.

javax.ws.rs.WebApplicationException

JAX-RS has a built-in unchecked exception that applications can throw. This exception is
preinitialized with either a Response or a particular status code:

public public class class WebApplicationException WebApplicationException extends extends RuntimeException {

public public WebApplicationException () {...}

public public WebApplicationException ( Response response ) {...}

public

public WebApplicationException ( int int status ) {...}

public public WebApplicationException ( Response . Status status ) {...}

public

public WebApplicationException ( Throwable cause ) {...}
public

public WebApplicationException ( Throwable cause ,
Response response ) {...}

public public WebApplicationException ( Throwable cause , int int status ) {...}

public public WebApplicationException ( Throwable cause ,

Response . Status status ) {...}