Examples for Chapter 11 - RESTful Java with JAX-RS 2.0 - page 315

high probability that it will be. A database application might use an incremented version
column to calculate the ETag value.

The CustomerResource class is expanded to support conditional GETs and PUTs. Let's take
a look at the relevant pieces of code:
src/main/java/com/restfully/shop/services/CustomerResource.java

@Path ( "/customers" )
public public class class CustomerResource CustomerResource

{
...

@GET
@Path ( "{id}" )
@Produces ( "application/xml" )
public public Response getCustomer ( @PathParam ( "id" ) int int id ,

@Context Request request ) {
Customer cust = customerDB . get ( id );
iif ( cust == null null )

{

throw throw new new WebApplicationException ( Response . Status . NOT_FOUND );

}

iif ( sent == null null ) System . out . println ( "No ETag sent by client" );

EntityTag tag = new new EntityTag ( Integer . toString ( cust . hashCode ()));

CacheControl cc = new new CacheControl ();

cc . setMaxAge ( 5 );

The getCustomer() method first starts out by retrieving the current Customer object identi-
fied by the id parameter. A current ETag value is created from the hash code of the Cus-
tomer object. A new Cache-Control header is instantiated as well.

Response . ResponseBuilder builder =
request . evaluatePreconditions ( tag );
iif ( builder != null

null ) {
System . out . println (
"** revalidation on the server was successful" );
builder . cacheControl ( cc );
return return builder . build ();

}

Next, Request.evaluatePreconditions() is called to perform a conditional GET. If the
client has sent an If-None-Match header that matches the calculated current ETag , the meth-