    001    // Copyright 2011 The Apache Software Foundation
    002    //
    003    // Licensed under the Apache License, Version 2.0 (the "License");
    004    // you may not use this file except in compliance with the License.
    005    // You may obtain a copy of the License at
    006    //
    007    // http://www.apache.org/licenses/LICENSE-2.0
    008    //
    009    // Unless required by applicable law or agreed to in writing, software
    010    // distributed under the License is distributed on an "AS IS" BASIS,
    011    // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    012    // See the License for the specific language governing permissions and
    013    // limitations under the License.
    014
    015    package org.apache.tapestry5.plastic;
    016
    017    /**
    018     * A {@link FieldConduit} is an object that effectively <em>replaces</em> the field in the instantiated object.
    019     * All reads and writes of the field are replaced with invocations on the conduit. Once a field's access is replaced
    020     * with a conduit, the field itself is no longer used. The conduit will even see initializations of the field.
    021     * <p>
    022     * In Aspect Oriented Programming terms, a FieldConduit allows you to advise read and write access to the field.
    023     * <p>
    024     * If a field has both a FieldConduit and a {@link FieldHandle}, then the methods of the FieldHandle will be connected
    025     * to the methods of the FieldConduit.
    026     */
    027    public interface FieldConduit<T>
    028    {
    029        /**
    030         * Invoked when the field is read.
    031         *
    032         * @param instance
    033         *            the instance containing the field
    034         * @param context
    035         *            (see {@link ClassInstantiator#with(Class, Object)})
    036         */
    037        T get(Object instance, InstanceContext context);
    038
    039        /**
    040         * Invoked when the field's value is updated.
    041         *
    042         * @param instance
    043         *            the instance containing the field
    044         * @param context
    045         *            (see {@link ClassInstantiator#with(Class, Object)})
    046         * @param newValue
    047         *            value assigned to the field
    048         */
    049        void set(Object instance, InstanceContext context, T newValue);
    050    }