RESTful Java with JAX-RS 2.0, 2nd Edition

Chapter 25. Examples for Chapter 11

In Chapter 11, you learned about HTTP caching techniques. Servers can tell HTTP clients if and how long they can cache retrieved resources. You can revalidate expired caches to avoid resending big messages by issuing conditional GET invocations. Conditional PUT operations can be invoked for safe concurrent updates.

Example ex11_1: Caching and Concurrent Updates

The example in this chapter expands on the CustomerResource example repeated throughout this book to support caching, conditional GETs, and conditional PUTs.

The Server Code

The first thing is to add a hashCode() method to the Customer class:

src/main/java/com/restfully/shop/domain/Customer.java

@XmlRootElement(name = "customer")
public class Customer
{
...
   @Override
   public int hashCode()
   {
      int result = id;
      result = 31 * result + (firstName != null
                                  ? firstName.hashCode() : 0);
      result = 31 * result + (lastName != null
                                  ? lastName.hashCode() : 0);
      result = 31 * result + (street != null
                                  ? street.hashCode() : 0);
      result = 31 * result + (city != null ? city.hashCode() : 0);
      result = 31 * result + (state != null ? state.hashCode() : 0);
      result = 31 * result + (zip != null ? zip.hashCode() : 0);
      result = 31 * result + (country != null
                                    ? country.hashCode() : 0);
      return result;
   }
}

This method is used in the CustomerResource class to generate semi-unique ETag header values. While a hash code calculated in this manner isn’t guaranteed to be unique, there is a high probability that it will be. A database ...