# CompositeContext.java

    /*
     * Copyright (c) 2007, Rickard Öberg. All Rights Reserved.
     *
     * 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.Qi4j;
    import org.qi4j.api.structure.Module;
    import org.qi4j.functional.Iterables;

    import static org.qi4j.functional.Iterables.toArray;

    /**
     * Thread-associated composites. This is basically a ThreadLocal which maintains a reference
     * to a TransientComposite instance for each thread. This can be used to implement various context
     * patterns without having to pass the context explicitly as a parameter to methods.
     */
    public class CompositeContext<T extends TransientComposite>
        extends ThreadLocal<T>
    {
        private Module module;
        private Class<T> type;

        public CompositeContext( Module module, Class<T> type )
        {
            this.module = module;
            this.type = type;
        }

        @Override
        protected T initialValue()
        {
            return module.newTransient( type );
        }

        @SuppressWarnings( "unchecked" )
        public T proxy()
        {
            TransientComposite composite = get();

            Iterable<Class<?>> types = Qi4j.FUNCTION_COMPOSITE_INSTANCE_OF.map( composite ).types();
            return (T) Proxy.newProxyInstance(
                composite.getClass().getClassLoader(),
                toArray( Class.class, Iterables.<Class>cast( types ) ),
                new ContextInvocationhandler() );
        }

        private class ContextInvocationhandler
            implements InvocationHandler
        {

            @Override
            public Object invoke( Object object, Method method, Object[] objects )
                throws Throwable
            {
                try
                {
                    return method.invoke( get(), objects );
                }
                catch( InvocationTargetException e )
                {
                    throw e.getTargetException();
                }
            }
        }
    }