package org.apache.beehive.controls.api.properties;
/*
* Copyright 2004 The Apache Software Foundation.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* $Header:$
*/
import java.lang.annotation.Annotation;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import org.apache.beehive.controls.api.properties.PropertyKey;
import org.apache.beehive.controls.api.properties.PropertyMap;
import org.apache.beehive.controls.api.properties.PropertySet;
/**
* The PropertySetProxy class is a dynamic proxy InvocationHandler class that exposes the
* values held within a PropertyMap as an Object implementing an annotation type interface.
* <p>
* This enables properties resolved using the PropertyMap's hiearchical resolution mechanism to
* be exposed to the client of the proxy in the same way that JSR-175 annotations are
* exposed using raw Java reflection APIs. A proxy of this type should behave identically
* to the one returned from a call to <code>AnnotatedElement.getAnnotation()</code>, but backed
* by a richer, more dynamic resolution mechanism.
*
* @see java.lang.reflect.Proxy
* @see java.lang.reflect.InvocationHandler
* @see java.lang.reflect.AnnotatedElement#getAnnotation
* @see org.apache.beehive.controls.api.properties.PropertySet
* @see org.apache.beehive.controls.api.properties.PropertyMap
*/
public class PropertySetProxy <T extends Annotation> implements InvocationHandler
{
/**
* Creates a new proxy instance implementing the PropertySet interface and backed
* by the data from the property map.
*
* @param propertySet an annotation type that has the PropertySet meta-annotation
* @param propertyMap the PropertyMap containing property values backing the proxy
* @return proxy that implements the PropertySet interface
*/
public static <T extends Annotation> T getProxy(Class<T> propertySet, PropertyMap propertyMap)
{
assert propertySet != null && propertyMap != null;
if (!propertySet.isAnnotation())
throw new IllegalArgumentException(propertySet + " is not an annotation type");
return (T) Proxy.newProxyInstance(propertySet.getClassLoader(),
new Class [] {propertySet },
new PropertySetProxy(propertySet, propertyMap));
}
/**
* Private constructor, called only from the getProxy factory method
*/
private PropertySetProxy(Class<T> propertySet, PropertyMap propertyMap)
{
_propertySet = propertySet;
_propertyMap = propertyMap;
}
//
// InvocationHandler.invoke
//
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable
{
// Handle cases where Object/Annotation methods are called on this
// proxy. We were getting null back from Annotation.annotationType.
Object value = null;
if (method.getDeclaringClass() == Object.class)
{
try {
if (method.getName().equals("getClass"))
{
value = _propertySet;
}
else
{
value = method.invoke(_propertyMap, args);
}
}
catch (Exception e)
{
e.printStackTrace();
}
}
else if (method.getDeclaringClass() == Annotation.class &&
method.getName().equals("annotationType"))
{
value = _propertySet;
}
else
{
// Query the nested value in the property map
PropertyKey key = new PropertyKey(_propertySet, method.getName());
value = _propertyMap.getProperty(key);
// If the returned value is itself a PropertyMap (i.e. a nested annotation type),
// then wrap it in a PropertySetProxy instance before returning.
if (value instanceof PropertyMap)
{
PropertyMap propertyMap = (PropertyMap)value;
value = getProxy(propertyMap.getMapClass(), propertyMap);
}
}
return value;
}
/**
* Returns the PropertySet annotation type associated with the proxy
*/
public Class<T> getPropertySet() { return _propertySet; }
/**
* Returns the underlying PropertyMap containing the property values exposed by the
* proxy.
*/
public PropertyMap getPropertyMap() { return _propertyMap; }
private Class<T> _propertySet;
private PropertyMap _propertyMap;
}