/*
 * Copyright 1999-2001,2004 The Apache Software Foundation.
 * 
 * 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.apache.catalina;


/**
 * <p>Interface describing a collection of Valves that should be executed
 * in sequence when the <code>invoke()</code> method is invoked.  It is
 * required that a Valve somewhere in the pipeline (usually the last one)
 * must process the request and create the corresponding response, rather
 * than trying to pass the request on.</p>
 *
 * <p>There is generally a single Pipeline instance associated with each
 * Container.  The container's normal request processing functionality is
 * generally encapsulated in a container-specific Valve, which should always
 * be executed at the end of a pipeline.  To facilitate this, the
 * <code>setBasic()</code> method is provided to set the Valve instance that
 * will always be executed last.  Other Valves will be executed in the order
 * that they were added, before the basic Valve is executed.</p>
 *
 * @author Craig R. McClanahan
 * @author Peter Donald
 * @version $Revision$ $Date$
 */

public interface Pipeline {


    // ------------------------------------------------------------- Properties


    /**
     * <p>Return the Valve instance that has been distinguished as the basic
     * Valve for this Pipeline (if any).
     */
    public Valve getBasic();


    /**
     * <p>Set the Valve instance that has been distinguished as the basic
     * Valve for this Pipeline (if any).  Prioer to setting the basic Valve,
     * the Valve's <code>setContainer()</code> will be called, if it
     * implements <code>Contained</code>, with the owning Container as an
     * argument.  The method may throw an <code>IllegalArgumentException</code>
     * if this Valve chooses not to be associated with this Container, or
     * <code>IllegalStateException</code> if it is already associated with
     * a different Container.</p>
     *
     * @param valve Valve to be distinguished as the basic Valve
     */
    public void setBasic(Valve valve);


    // --------------------------------------------------------- Public Methods


    /**
     * <p>Add a new Valve to the end of the pipeline associated with this
     * Container.  Prior to adding the Valve, the Valve's
     * <code>setContainer()</code> method will be called, if it implements
     * <code>Contained</code>, with the owning Container as an argument.
     * The method may throw an
     * <code>IllegalArgumentException</code> if this Valve chooses not to
     * be associated with this Container, or <code>IllegalStateException</code>
     * if it is already associated with a different Container.</p>
     *
     * @param valve Valve to be added
     *
     * @exception IllegalArgumentException if this Container refused to
     *  accept the specified Valve
     * @exception IllegalArgumentException if the specifie Valve refuses to be
     *  associated with this Container
     * @exception IllegalStateException if the specified Valve is already
     *  associated with a different Container
     */
    public void addValve(Valve valve);


    /**
     * Return the set of Valves in the pipeline associated with this
     * Container, including the basic Valve (if any).  If there are no
     * such Valves, a zero-length array is returned.
     */
    public Valve[] getValves();


    /**
     * Remove the specified Valve from the pipeline associated with this
     * Container, if it is found; otherwise, do nothing.  If the Valve is
     * found and removed, the Valve's <code>setContainer(null)</code> method
     * will be called if it implements <code>Contained</code>.
     *
     * @param valve Valve to be removed
     */
    public void removeValve(Valve valve);


    /**
     * <p>Return the Valve instance that has been distinguished as the basic
     * Valve for this Pipeline (if any).
     */
    public Valve getFirst();


}