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.ioc.services;
014
015import org.slf4j.Logger;
016
017import java.util.Collections;
018import java.util.List;
019
020/**
021 * Creates a pipeline from a service interface and an ordered list of filters. Each filter is defined in terms of a
022 * filter interface: the filter interface is a variant of the service interface, where each method has an additional
023 * parameter that is an instance of the service interface. Typically, this service parameter (often named "delegate") is
024 * either the first or the last parameter of each method.
025 *
026 * The implementation of a filter method is expected to pass all of its parameters to the service instance passed into
027 * it.
028 *
029 * The interesting thing is that there may be multiple filters in the pipeline. A fabricated "bridge" object (that
030 * implements the service interface) is created to let each filter invoke methods on the next filter down the pipeline.
031 * This simplifies the model for creating pipelines, as each filter is coded as if it was directly "in front of" the
032 * terminator. In fact, it may be indirectly invoking methods on the next filter in the pipeline via a bridge instance.
033 *
034 * The builder is fairly smart about matching up service interface methods to filter interface methods, but keeping it
035 * simple is also a good idea.  By convention, the final parameter of each filter method is the delegate object (the bridge or terminator).
036 */
037public interface PipelineBuilder
038{
039    /**
040     * Creates a pipeline from the filters and a terminator.
041     *
042     * @param <S>              service type
043     * @param <F>              filter type
044     * @param logger           logs any warnings generated when constructing the pipeline
045     * @param serviceInterface defines the interface for the pipeline
046     * @param filterInterface  the filter interface, contributed into the pipeline
047     * @param filters          sorted list of filters
048     * @param terminator       end of the pipeline
049     * @return an object that encapsulates the filters and the terminator
050     */
051    <S, F> S build(Logger logger, Class<S> serviceInterface, Class<F> filterInterface, List<F> filters, S terminator);
052
053    /**
054     * Creates a pipeline from just the filters. A {@link DefaultImplementationBuilder default implementation} is
055     * created as the terminator.
056     *
057     * @param <S>              service type
058     * @param <F>              filter type
059     * @param logger           logs any warnings generated when constructing the pipeline
060     * @param serviceInterface defines the interface for the pipeline
061     * @param filterInterface  the filter interface, contributed into the pipeline
062     * @param filters          sorted list of filters
063     * @return an object that encapsulates the filters and the default implementation
064     */
065    <S, F> S build(Logger logger, Class<S> serviceInterface, Class<F> filterInterface, List<F> filters);
066
067    /**
068     * The pipelines assembled so far, in the order they were assembled.
069     *
070     * <p>A pipeline is assembled when the service it implements is first realized, so the list grows as the application runs.
071     *
072     * @return the assembled pipelines, or an empty list for an implementation that does not keep track of them
073     * @since 5.9.2
074     */
075    default List<AssembledPipeline> getAssembledPipelines()
076    {
077        return Collections.emptyList();
078    }
079
080}