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// ========================================================================
// Copyright 2004-2005 Mort Bay Consulting Pty. Ltd.
// ------------------------------------------------------------------------
// 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.mortbay.component;

import java.util.EventListener;

/* ------------------------------------------------------------ */
/**
 * The lifecycle interface for generic components.
 * 

 * Classes implementing this interface have a defined life cycle
 * defined by the methods of this interface.
 *
 * @author Greg Wilkins (gregw)
 */
public interface LifeCycle
{
    /* ------------------------------------------------------------ */
    /**
     * Starts the component.
     * @throws Exception If the component fails to start
     * @see #isStarted()
     * @see #stop()
     * @see #isFailed()
     */
    public void start()
        throws Exception;

    /* ------------------------------------------------------------ */
    /**
     * Stops the component.
     * The component may wait for current activities to complete
     * normally, but it can be interrupted.
     * @exception Exception If the component fails to stop
     * @see #isStopped()
     * @see #start()
     * @see #isFailed()
     */
    public void stop()
        throws Exception;

    /* ------------------------------------------------------------ */
    /**
     * @return true if the component is starting or has been started.
     */
    public boolean isRunning();

    /* ------------------------------------------------------------ */
    /**
     * @return true if the component has been started.
     * @see #start()
     * @see #isStarting()
     */
    public boolean isStarted();

    /* ------------------------------------------------------------ */
    /**
     * @return true if the component is starting.
     * @see #isStarted()
     */
    public boolean isStarting();

    /* ------------------------------------------------------------ */
    /**
     * @return true if the component is stopping.
     * @see #isStopped()
     */
    public boolean isStopping();

    /* ------------------------------------------------------------ */
    /**
     * @return true if the component has been stopped.
     * @see #stop()
     * @see #isStopping()
     */
    public boolean isStopped();

    /* ------------------------------------------------------------ */
    /**
     * @return true if the component has failed to start or has failed to stop.
     */
    public boolean isFailed();
    
    /* ------------------------------------------------------------ */
    public void addLifeCycleListener(LifeCycle.Listener listener);

    /* ------------------------------------------------------------ */
    public void removeLifeCycleListener(LifeCycle.Listener listener);
    

    /* ------------------------------------------------------------ */
    /** Listener.
     * A listener for Lifecycle events.
     */
    public interface Listener extends EventListener
    {
        public void lifeCycleStarting(LifeCycle event);
        public void lifeCycleStarted(LifeCycle event);
        public void lifeCycleFailure(LifeCycle event,Throwable cause);
        public void lifeCycleStopping(LifeCycle event);
        public void lifeCycleStopped(LifeCycle event);
    }
}