| A factory class that creates lazy init proxies given a type and a
IProxyTargetLocator used to retrieve the object the proxy will
represent.
A lazy init proxy waits until the first method invocation before it uses the
IProxyTargetLocator to retrieve the object to which the method
invocation will be forwarded.
This factory creates two kinds of proxies: A standard dynamic proxy when the
specified type is an interface, and a CGLib proxy when the specified type is
a concrete class.
The general use case for such a proxy is to represent a dependency that
should not be serialized with a wicket page or
IModel . The solution
is to serialize the proxy and the
IProxyTargetLocator instead of the
dependency, and be able to look up the target object again when the proxy is
deserialized and accessed. A good strategy for achieving this is to have a
static lookup in the
IProxyTargetLocator , this keeps its size small
and makes it safe to serialize.
Example:
class UserServiceLocator implements IProxyTargetLocator
{
public static final IProxyTargetLocator INSTANCE = new UserServiceLocator();
Object locateProxyObject()
{
MyApplication app = (MyApplication) Application.get();
return app.getUserService();
}
}
class UserDetachableModel extends LoadableModel
{
private UserService svc;
private long userId;
public UserDetachableModel(long userId, UserService svc)
{
this.userId = userId;
this.svc = svc;
}
public Object load()
{
return svc.loadUser(userId);
}
}
UserService service = LazyInitProxyFactory.createProxy(UserService.class,
UserServiceLocator.INSTANCE);
UserDetachableModel model = new UserDetachableModel(10, service);
The detachable model in the example above follows to good citizen pattern and
is easy to unit test. These are the advantages gained through the use of the
lazy init proxies.
author:
Igor Vaynberg (ivaynberg) | 