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.internal.services;
014
015import org.apache.tapestry5.commons.services.PlasticProxyFactory;
016import org.apache.tapestry5.ioc.annotations.UsesMappedConfiguration;
017import org.apache.tapestry5.services.transform.ControlledPackageType;
018
019/**
020 * Creates {@link org.apache.tapestry5.internal.services.Instantiator}s for components, based on component class name.
021 * This will involve transforming the component's class before it is loaded.
022 *
023 * In addition, a source acts as an event hub for {@link org.apache.tapestry5.commons.services.InvalidationListener}s, so that
024 * any information derived from loaded classes can be discarded and rebuilt when classes change.
025 *
026 * The strategy used is that when <em>any</em> class (in a controlled package) changes, the entire class loader is
027 * discarded, along with any instances derived from those classes. A new class loader is created, and then invalidation
028 * events are fired to listeners.
029 *
030 * Starting in Tapestry 5.3, the packages that are loaded are controlled by a configuration that maps package names to
031 * {@link ControlledPackageType}s.
032 */
033@UsesMappedConfiguration(key = String.class, value = ControlledPackageType.class)
034public interface ComponentInstantiatorSource
035{
036
037    /**
038     * Given the name of a component class, provides an instantiator for that component. Instantiators are cached, so
039     * repeated calls to this method with the same class name will return the same instance; however, callers should
040     * also be aware that the instantiators may lose validity after an invalidation (caused by changes to external Java
041     * class files).
042     *
043     * @param classname FQCN to find (and perhaps transform and load)
044     * @return an object which can instantiate an instance of the component
045     */
046    Instantiator getInstantiator(String classname);
047
048    /**
049     * Checks to see if a fully qualified class name exists. This method appears to exist only for testing.
050     *
051     * @param className name of class to check
052     * @return true if the class exists (there's a ".class" file), false otherwise
053     */
054    boolean exists(String className);
055
056    /**
057     * Returns a proxy factory that can be used to generate additional classes around enhanced classes, or create
058     * subclasses of enhanced classes.
059     *
060     * @since 5.3
061     */
062    PlasticProxyFactory getProxyFactory();
063
064    /**
065     * Forces invalidation logic, as if a component class on the disk had changed, forcing a reload
066     * of all pages and components.
067     *
068     * @since 5.3
069     */
070    void forceComponentInvalidation();
071}