core/api/src/main/java/org/qi4j/api/composite/DecoratorMixin.java

/*
 * Copyright 2009 Niclas Hedhman.
 *
 * 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.
 */
package org.qi4j.api.composite;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import org.qi4j.api.injection.scope.Uses;

/**
 * Generic decorator mixin that allows a Composite to wrap
 * any other Composite as long as they share an interface.
 * <p>
 * Can be used to effectively implement
 * singleton mixins, since the decorated object can be shared between
 * many instances.
 * </p>
 */
public class DecoratorMixin
    implements InvocationHandler
{
    private Object delegate;

    public DecoratorMixin( @Uses Object delegate )
    {
        if( delegate instanceof Class )
        {
            Thread.dumpStack();
        }
        this.delegate = delegate;
    }

    @Override
    public Object invoke( Object object, Method method, Object[] args )
        throws Throwable
    {
        if( delegate instanceof InvocationHandler )
        {
            InvocationHandler handler = (InvocationHandler) delegate;
            return handler.invoke( object, method, args );
        }
        else
        {
            try
            {
                return method.invoke( delegate, args );
            }
            catch( InvocationTargetException e )
            {
                throw e.getCause();
            }
            catch( IllegalArgumentException e )
            {
                String message = constructMessage( method, args );
                throw new IllegalArgumentException( message, e );
            }
        }
    }

    private String constructMessage( Method method, Object[] args )
    {
        StringBuilder builder = new StringBuilder();
        builder.append( "\nmethod: " );
        builder.append( method.getDeclaringClass().getName() );
        builder.append( "." );
        builder.append( method.getName() );
        builder.append( "\ndelegate: " );
        builder.append( delegate );
        builder.append( "\ndelegateType: " );
        builder.append( delegate == null ? "n/a" : delegate.getClass().getName() );
        builder.append( "\narguments: \n" );
        for( Object arg : args )
        {
            builder.append( "    " );
            Class argClass = arg.getClass();
            if( Proxy.isProxyClass( argClass ) )
            {
                builder.append( Proxy.getInvocationHandler( arg ).getClass().getName() );
            }
            else
            {
                builder.append( argClass.getName() );
            }
            builder.append( '\n' );
        }
        return builder.toString();
    }
}