5.6. EntityNameResolvers

/**
 * A very trivial JDK Proxy InvocationHandler implementation where we proxy an interface as
 * the domain model and simply store persistent state in an internal Map.  This is an extremely
 * trivial example meant only for illustration.
 */
public final class DataProxyHandler implements InvocationHandler {
    private String entityName;
    private HashMap data = new HashMap();

    public DataProxyHandler(String entityName, Serializable id) {
        this.entityName = entityName;
        data.put( "Id", id );
    }

    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        String methodName = method.getName();
        if ( methodName.startsWith( "set" ) ) {
            String propertyName = methodName.substring( 3 );
            data.put( propertyName, args[0] );
        }
        else if ( methodName.startsWith( "get" ) ) {
            String propertyName = methodName.substring( 3 );
            return data.get( propertyName );
        }
        else if ( "toString".equals( methodName ) ) {
            return entityName + "#" + data.get( "Id" );
        }
        else if ( "hashCode".equals( methodName ) ) {
            return new Integer( this.hashCode() );
        }
        return null;
    }

    public String getEntityName() {
        return entityName;
    }

    public HashMap getData() {
        return data;
    }
}

/**
 *
 */
public class ProxyHelper {
    public static String extractEntityName(Object object) {
        // Our custom java.lang.reflect.Proxy instances actually bundle
        // their appropriate entity name, so we simply extract it from there
        // if this represents one of our proxies; otherwise, we return null
        if ( Proxy.isProxyClass( object.getClass() ) ) {
            InvocationHandler handler = Proxy.getInvocationHandler( object );
            if ( DataProxyHandler.class.isAssignableFrom( handler.getClass() ) ) {
                DataProxyHandler myHandler = ( DataProxyHandler ) handler;
                return myHandler.getEntityName();
            }
        }
        return null;
    }

    // various other utility methods ....

}

/**
 * The EntityNameResolver implementation.
 * IMPL NOTE : An EntityNameResolver really defines a strategy for how entity names should be
 * resolved.  Since this particular impl can handle resolution for all of our entities we want to
 * take advantage of the fact that SessionFactoryImpl keeps these in a Set so that we only ever
 * have one instance registered.  Why?  Well, when it comes time to resolve an entity name,
 * Hibernate must iterate over all the registered resolvers.  So keeping that number down
 * helps that process be as speedy as possible.  Hence the equals and hashCode impls
 */
public class MyEntityNameResolver implements EntityNameResolver {
    public static final MyEntityNameResolver INSTANCE = new MyEntityNameResolver();

    public String resolveEntityName(Object entity) {
        return ProxyHelper.extractEntityName( entity );
    }

    public boolean equals(Object obj) {
        return getClass().equals( obj.getClass() );
    }

    public int hashCode() {
        return getClass().hashCode();
    }
}

public class MyEntityTuplizer extends PojoEntityTuplizer {
    public MyEntityTuplizer(EntityMetamodel entityMetamodel, PersistentClass mappedEntity) {
        super( entityMetamodel, mappedEntity );
    }

    public EntityNameResolver[] getEntityNameResolvers() {
        return new EntityNameResolver[] { MyEntityNameResolver.INSTANCE };
    }

    public String determineConcreteSubclassEntityName(Object entityInstance, SessionFactoryImplementor factory) {
        String entityName = ProxyHelper.extractEntityName( entityInstance );
        if ( entityName == null ) {
            entityName = super.determineConcreteSubclassEntityName( entityInstance, factory );
        }
        return entityName;
    }

    ...
}