/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.
*/
package org.apache.commons.proxy.factory.util;
import org.apache.commons.proxy.ProxyFactory;
import org.apache.commons.proxy.exception.ProxyFactoryException;
import java.lang.reflect.Constructor;
import java.lang.reflect.Modifier;
import java.util.Collection;
import java.util.LinkedList;
import java.util.List;
/**
* A useful superclass for a {@link ProxyFactory} which supports subclassing rather than merely implementing interfaces.
*
* @author James Carman
* @since 1.0
*/
public abstract class AbstractSubclassingProxyFactory extends ProxyFactory
{
//----------------------------------------------------------------------------------------------------------------------
// Static Methods
//----------------------------------------------------------------------------------------------------------------------
private static boolean hasSuitableDefaultConstructor( Class superclass )
{
final Constructor[] declaredConstructors = superclass.getDeclaredConstructors();
for( int i = 0; i < declaredConstructors.length; i++ )
{
Constructor constructor = declaredConstructors[i];
if( constructor.getParameterTypes().length == 0 && ( Modifier.isPublic( constructor.getModifiers() ) ||
Modifier.isProtected( constructor.getModifiers() ) ) )
{
return true;
}
}
return false;
}
/**
* Returns the <code>proxyClasses</code> transformed into an array of only the interface classes.
*
* @param proxyClasses the proxy classes
* @return the <code>proxyClasses</code> transformed into an array of only the interface classes
*/
protected static Class[] toInterfaces( Class[] proxyClasses )
{
final Collection interfaces = new LinkedList();
for( int i = 0; i < proxyClasses.length; i++ )
{
Class proxyInterface = proxyClasses[i];
if( proxyInterface.isInterface() )
{
interfaces.add( proxyInterface );
}
}
return ( Class[] ) interfaces.toArray( new Class[interfaces.size()] );
}
private static Class[] toNonInterfaces( Class[] proxyClasses )
{
final List superclasses = new LinkedList();
for( int i = 0; i < proxyClasses.length; i++ )
{
Class proxyClass = proxyClasses[i];
if( !proxyClass.isInterface() )
{
superclasses.add( proxyClass );
}
}
return ( Class[] ) superclasses.toArray( new Class[superclasses.size()] );
}
//----------------------------------------------------------------------------------------------------------------------
// Other Methods
//----------------------------------------------------------------------------------------------------------------------
/**
* Returns true if a suitable superclass can be found, given the desired <code>proxyClasses</code>.
*
* @param proxyClasses the proxy classes
* @return true if a suitable superclass can be found, given the desired <code>proxyClasses</code>
*/
public boolean canProxy( Class[] proxyClasses )
{
try
{
getSuperclass( proxyClasses );
return true;
}
catch( ProxyFactoryException e )
{
return false;
}
}
/**
* Returns either {@link Object} if all of the <code>proxyClasses</code> are interfaces or the single non-interface
* class from <code>proxyClasses</code>.
*
* @param proxyClasses the proxy classes
* @return either {@link Object} if all of the <code>proxyClasses</code> are interfaces or the single non-interface
* class from <code>proxyClasses</code>
* @throws ProxyFactoryException if multiple non-interface classes are contained in <code>proxyClasses</code> or any
* of the non-interface classes are final
*/
public static Class getSuperclass( Class[] proxyClasses )
{
final Class[] superclasses = toNonInterfaces( proxyClasses );
switch( superclasses.length )
{
case 0:
return Object.class;
case 1:
final Class superclass = superclasses[0];
if( Modifier.isFinal( superclass.getModifiers() ) )
{
throw new ProxyFactoryException(
"Proxy class cannot extend " + superclass.getName() + " as it is final." );
}
if( !hasSuitableDefaultConstructor( superclass ) )
{
throw new ProxyFactoryException( "Proxy class cannot extend " + superclass.getName() +
", because it has no visible \"default\" constructor." );
}
return superclass;
default:
final StringBuffer errorMessage = new StringBuffer( "Proxy class cannot extend " );
for( int i = 0; i < superclasses.length; i++ )
{
Class c = superclasses[i];
errorMessage.append( c.getName() );
if( i != superclasses.length - 1 )
{
errorMessage.append( ", " );
}
}
errorMessage.append( "; multiple inheritance not allowed." );
throw new ProxyFactoryException( errorMessage.toString() );
}
}
}