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 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 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)

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	LazyInitProxyFactory.IWriteReplace This interface is used to make the proxy forward writeReplace() call to the handler instead of invoking it on itself.
static class	LazyInitProxyFactory.SerializableNoOpCallback Serializable implementation of the NoOp callback.

Constructor Summary

Constructors

Constructor and Description
LazyInitProxyFactory()

Method Summary

Methods

Modifier and Type	Method and Description
static Object	createProxy(Class<?> type, IProxyTargetLocator locator) Create a lazy init proxy for the specified type.
static boolean	isEqualsMethod(Method method) Checks if the method is derived from Object.equals()
static boolean	isFinalizeMethod(Method method) Checks if the method is derived from Object.finalize()
static boolean	isHashCodeMethod(Method method) Checks if the method is derived from Object.hashCode()
static boolean	isToStringMethod(Method method) Checks if the method is derived from Object.toString()
static boolean	isWriteReplaceMethod(Method method) Checks if the method is the writeReplace method

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

LazyInitProxyFactory

public LazyInitProxyFactory()

Method Detail

createProxy

public static Object createProxy(Class<?> 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