    001// Licensed under the Apache License, Version 2.0 (the "License");
    002// you may not use this file except in compliance with the License.
    003// You may obtain a copy of the License at
    004//
    005//     http://www.apache.org/licenses/LICENSE-2.0
    006//
    007// Unless required by applicable law or agreed to in writing, software
    008// distributed under the License is distributed on an "AS IS" BASIS,
    009// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    010// See the License for the specific language governing permissions and
    011// limitations under the License.
    012
    013package org.apache.tapestry5.services;
    014
    015import org.apache.tapestry5.PropertyConduit;
    016
    017/**
    018 * A source for {@link org.apache.tapestry5.PropertyConduit}s, which can be thought of as a compiled property path
    019 * expression. PropertyConduits are the basis of the "prop:" binding factory, thus this service defines the expression
    020 * format used by the {@link org.apache.tapestry5.internal.bindings.PropBindingFactory}.
    021 */
    022public interface PropertyConduitSource
    023{
    024    /**
    025     * Returns a property conduit instance for the given expression. PropertyConduitSource caches the conduits it
    026     * returns, so despite the name, this method does not always create a <em>new</em> conduit. The cache is cleared if
    027     * a change to component classes is observed.
    028     *
    029     * Callers of this method should observe notifications from the {@link org.apache.tapestry5.services.InvalidationEventHub}
    030     * for {@link org.apache.tapestry5.services.ComponentClasses} and discard any aquired conduits; failure to do so
    031     * will create memory leaks whenever component classes change (the conduits will keep references to the old classes
    032     * and classloaders).
    033     *
    034     * @param rootType   the type of the root object to which the expression is applied
    035     * @param expression expression to be evaluated on instances of the root class
    036     * @return RuntimeException if the expression is invalid (poorly formed, references non-existent properties, etc.)
    037     */
    038    PropertyConduit create(Class rootType, String expression);
    039}