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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.apache.catalina;

import java.beans.PropertyChangeListener;

/**
 * A Loader represents a Java ClassLoader implementation that can
 * be used by a Container to load class files (within a repository associated
 * with the Loader) that are designed to be reloaded upon request, as well as
 * a mechanism to detect whether changes have occurred in the underlying
 * repository.
 * 
 * In order for a Loader implementation to successfully operate
 * with a Context implementation that implements reloading, it
 * must obey the following constraints:
 * 

 * Must implement Lifecycle so that the Context can indicate
 *     that a new class loader is required.
 * 
The start() method must unconditionally create a new
 *     ClassLoader implementation.
 * 
The stop() method must throw away its reference to the
 *     ClassLoader previously utilized, so that the class loader,
 *     all classes loaded by it, and all objects of those classes, can be
 *     garbage collected.
 * 
Must allow a call to stop() to be followed by a call to
 *     start() on the same Loader instance.
 * 
Based on a policy chosen by the implementation, must call the
 *     Context.reload() method on the owning Context
 *     when a change to one or more of the class files loaded by this class
 *     loader is detected.
 * 
 *
 * @author Craig R. McClanahan
 */
public interface Loader {


    /**
     * Execute a periodic task, such as reloading, etc. This method will be
     * invoked inside the classloading context of this container. Unexpected
     * throwables will be caught and logged.
     */
    public void backgroundProcess();


    /**
     * @return the Java class loader to be used by this Container.
     */
    public ClassLoader getClassLoader();


    /**
     * @return the Context with which this Loader has been associated.
     */
    public Context getContext();


    /**
     * Set the Context with which this Loader has been associated.
     *
     * @param context The associated Context
     */
    public void setContext(Context context);


    /**
     * @return the "follow standard delegation model" flag used to configure
     * our ClassLoader.
     */
    public boolean getDelegate();


    /**
     * Set the "follow standard delegation model" flag used to configure
     * our ClassLoader.
     *
     * @param delegate The new flag
     */
    public void setDelegate(boolean delegate);


    /**
     * Add a property change listener to this component.
     *
     * @param listener The listener to add
     */
    public void addPropertyChangeListener(PropertyChangeListener listener);


    /**
     * Has the internal repository associated with this Loader been modified,
     * such that the loaded classes should be reloaded?
     *
     * @return true when the repository has been modified,
     *         false otherwise
     */
    public boolean modified();


    /**
     * Remove a property change listener from this component.
     *
     * @param listener The listener to remove
     */
    public void removePropertyChangeListener(PropertyChangeListener listener);
}