Module org.apache.wicket.ioc
Package org.apache.wicket.proxy

Class LazyInitProxyFactory

java.lang.Object
org.apache.wicket.proxy.LazyInitProxyFactory
public class LazyInitProxyFactory extends Object
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 ByteBuddy 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 LoadableDetachableModel
 {
        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)

  • Constructor Details

  • Method Details

    • createProxy

      public static <T> T createProxy(Class<T> type, IProxyTargetLocator locator)
      Create a lazy init proxy for the specified type. The target object will be located using the provided locator upon first method invocation.
      Parameters:
      type - type that proxy will represent
      locator - object locator that will locate the object the proxy represents
      Returns:
      lazily initializable proxy

    • isEqualsMethod

      public static boolean isEqualsMethod(Method method)
      Checks if the method is derived from Object.equals()
      Parameters:
      method - method being tested
      Returns:
      true if the method is derived from Object.equals(), false otherwise

    • isHashCodeMethod

      public static boolean isHashCodeMethod(Method method)
      Checks if the method is derived from Object.hashCode()
      Parameters:
      method - method being tested
      Returns:
      true if the method is defined from Object.hashCode(), false otherwise

    • isToStringMethod

      public static boolean isToStringMethod(Method method)
      Checks if the method is derived from Object.toString()
      Parameters:
      method - method being tested
      Returns:
      true if the method is defined from Object.toString(), false otherwise

    • isFinalizeMethod

      public static boolean isFinalizeMethod(Method method)
      Checks if the method is derived from Object.finalize()
      Parameters:
      method - method being tested
      Returns:
      true if the method is defined from Object.finalize(), false otherwise

    • isWriteReplaceMethod

      public static boolean isWriteReplaceMethod(Method method)
      Checks if the method is the writeReplace method
      Parameters:
      method - method being tested
      Returns:
      true if the method is the writeReplace method, false otherwise