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The core of Cocoon 3. A Servlet API independent implementation of pipelines.
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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.cocoon.pipeline;

import java.io.OutputStream;
import java.util.Map;

import org.apache.cocoon.pipeline.component.Consumer;
import org.apache.cocoon.pipeline.component.Finisher;
import org.apache.cocoon.pipeline.component.PipelineComponent;
import org.apache.cocoon.pipeline.component.Producer;
import org.apache.cocoon.pipeline.component.Starter;

/**
 * 
 * A pipeline expects one or more {@link PipelineComponent}s that passed by
 * using {@link #addComponent(PipelineComponent)}. Then these components get
 * linked with each other in the order they were added. The
 * {@link #setup(OutputStream, Map)} method, calls the setup method on all
 * pipeline components and assembles the pipeline. Finally the
 * {@link #execute()} method produces the result and writes it to the
 * {@link OutputStream} which has been passed to the
 * {@link #setup(OutputStream, Map)} method.
 * 
 *
 * 
 * A pipeline works based on two fundamental concepts:
 *
 * 

 * The first component of a pipeline is of type {@link Starter}. The last
 * component is of type {@link Finisher}. 
 * In order to link components with each other, the first has to be a
 * {@link Producer}, the latter {@link Consumer}. 
 * 
 *
 * 
 * When the pipeline links the components, it merely checks whether the above
 * mentioned interfaces are present. So the pipeline does not know about the
 * specific capabilities or the compatibility of the components. It is the
 * responsibility of the {@link Producer} to decide whether a specific
 * {@link Consumer} can be linked to it or not (that is, whether it can produce
 * output in the desired format of the {@link Consumer} or not). It is also
 * conceivable that a {@link Producer} is capable of accepting different types
 * of {@link Consumer}s and adjust the output format according to the actual
 * {@link Consumer}.
 * 
 */
public interface Pipeline {

    /**
     * Add a {@link PipelineComponent} to the pipeline. The order of when the
     * components are passed is significant.
     *
     * @param pipelineComponent The {@link PipelineComponent}.
     */
    void addComponent(T pipelineComponent);

    /**
     * After the pipeline has been setup ({@link #setup(OutputStream, Map)},
     * this method can be invoked in order to produce the result.
     *
     * @throws Exception Any problem that might occur while processing the
     *             pipeline.
     */
    void execute() throws Exception;

    /**
     * Get the mime-type {@linkref http://tools.ietf.org/html/rfc2046} of the
     * content produced by the pipeline.
     *
     * @return The mime-type of the content.
     */
    String getContentType();

    /**
     * Get the time of the last modification.
     *
     * @return The last modification date
     */
    long getLastModified();

    /**
     * After the pipeline has been prepared ({@link #addComponent(PipelineComponent)},
     * this method can be invoked in order to setup and initialize the pipeline
     * and its components.
     *
     * @param outputStream An {@link OutputStream} where the pipeline execution
     *            result is written.
     */
    void setup(OutputStream outputStream);

    /**
     * The same as {@link #setup(OutputStream)} but also allows passing
     * parameters to the pipeline components.
     *
     * @param outputStream An {@link OutputStream} where the pipeline execution
     *            result is written.
     * @param parameters A {@link Map} of parameters that are available to all
     *            {@link PipelineComponent}s.
     */
    void setup(OutputStream outputStream, Map parameters);

    /**
     * Pass pipeline specific configuration parameters to the pipeline component
     * in a generic way. This is useful in environments that automatically
     * assemble pipelines with their components and can't use the pipeline's
     * constructors or setters.
     *
     * @param configuration The {@link Map} of configuration parameters.
     */
    void setConfiguration(Map parameters);
}