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• Stages.java

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org.glassfish.jersey.process.internal.Stages Maven / Gradle / Ivy

/*
 * Copyright (c) 2010, 2019 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0, which is available at
 * http://www.eclipse.org/legal/epl-2.0.
 *
 * This Source Code may also be made available under the following Secondary
 * Licenses when the conditions for such availability set forth in the
 * Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
 * version 2 with the GNU Classpath Exception, which is available at
 * https://www.gnu.org/software/classpath/license.html.
 *
 * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
 */

package org.glassfish.jersey.process.internal;

import java.util.Deque;
import java.util.LinkedList;
import java.util.function.Function;

import org.glassfish.jersey.internal.util.collection.Ref;
import org.glassfish.jersey.process.Inflector;

/**
 * A stage-related collection of utility methods.
 *
 * @author Marek Potociar
 */
public final class Stages {
    private static final ChainableStage IDENTITY = new AbstractChainableStage() {

        @Override
        public Continuation apply(Object o) {
            //noinspection unchecked
            return Continuation.of(o, getDefaultNext());
        }
    };

    /**
     * Prevents instantiation.
     */
    private Stages() {
    }

    /**
     * Get a chainable "identity" stage.
     *
     * This stage, when applied returns the unmodified input data object
     * as part of it's continuation.
     *
     * @param  data type transformable by the stage.
     * @return identity stage.
     */
    public static  ChainableStage identity() {
        //noinspection unchecked
        return IDENTITY;
    }

    /**
     * Creates a terminal {@link Stage} that implements {@link Inflecting}
     * interface and returns the provided {@link Inflector} instance
     * when the {@link Inflecting#inflector()} method is called.
     *
     * @param     data type transformable by the stage and returned inflector.
     * @param   type of result produced by a successful inflector data transformation.
     * @param inflector a request to response transformation to be wrapped in
     *                  a stage.
     * @return a stage that wraps the supplied {@code Inflector}.
     */
    @SuppressWarnings("unchecked")
    public static  Stage asStage(final Inflector inflector) {
        return new InflectingStage(inflector);
    }

    private static class InflectingStage implements Stage, Inflecting {

        private final Inflector inflector;

        public InflectingStage(Inflector inflector) {
            this.inflector = inflector;
        }

        @Override
        public Inflector inflector() {
            return inflector;
        }

        @Override
        public Stage.Continuation apply(DATA request) {
            return Continuation.of(request);
        }
    }

    /**
     * (Optionally) extracts an {@link Inflector inflector} from a processing stage,
     * provided the stage implements {@link Inflecting} interface. Otherwise method
     * returns {@code null}.
     *
     * @param    data type transformable by the stage and returned inflector.
     * @param  type of result produced by a successful inflector data transformation.
     * @param stage    a stage to extract the inflector from.
     * @return extracted inflector if present, {@code null} otherwise.
     */
    @SuppressWarnings("unchecked")
    public static > T extractInflector(Object stage) {
        if (stage instanceof Inflecting) {
            return (T) ((Inflecting) stage).inflector();
        }

        return null;
    }

    /**
     * Start building a stage chain.
     *
     * @param transformation root transformation function.
     * @return linear accepting chain builder.
     */
    public static  Stage.Builder chain(Function transformation) {
        return new StageChainBuilder(transformation);
    }

    /**
     * Start building a stage chain.
     *
     * @param rootStage root {@link ChainableStage chainable linear stage}.
     * @return linear accepting chain builder.
     */
    public static  Stage.Builder chain(ChainableStage rootStage) {
        return new StageChainBuilder(rootStage);
    }

    /**
     * Run the data through a chain of stages identified by the root stage.
     *
     * @param     processed data type.
     * @param data      data to be processed.
     * @param rootStage root stage of the stage chain.
     * @return processing result.
     */
    public static  DATA process(DATA data, Stage rootStage) {
        Stage.Continuation continuation = Stage.Continuation.of(data, rootStage);
        Stage currentStage;
        while ((currentStage = continuation.next()) != null) {
            continuation = currentStage.apply(continuation.result());
        }
        return continuation.result();
    }

    /**
     * Run the data through a chain of stages identified by the root stage.
     *
     * If an inflector is found in the leaf stage, it's reference is set into the {@code inflectorRef}
     * parameter.
     *
     * @param        processed data type.
     * @param data         data to be processed.
     * @param rootStage    root stage of the stage chain.
     * @param inflectorRef a mutable reference to an inflector.
     * @return processing result.
     */
    public static > DATA process(
            DATA data,
            Stage rootStage,
            Ref inflectorRef) {

        Stage lastStage = rootStage;
        Stage.Continuation continuation = Stage.Continuation.of(data, lastStage);
        while (continuation.next() != null) {
            lastStage = continuation.next();
            continuation = lastStage.apply(continuation.result());
        }

        inflectorRef.set(Stages.extractInflector(lastStage));

        return continuation.result();
    }

    private static class StageChainBuilder implements Stage.Builder {

        private final Deque> transformations = new LinkedList>();
        private Stage rootStage;
        private ChainableStage lastStage;

        private StageChainBuilder(Function transformation) {
            transformations.push(transformation);
        }

        private StageChainBuilder(ChainableStage rootStage) {
            this.rootStage = rootStage;
            this.lastStage = rootStage;
        }

        @Override
        public Stage.Builder to(Function transformation) {
            transformations.push(transformation);
            return this;
        }

        @Override
        public Stage.Builder to(final ChainableStage stage) {
            addTailStage(stage);
            lastStage = stage;

            return this;
        }

        private void addTailStage(Stage lastStage) {
            Stage tail = lastStage;
            if (!transformations.isEmpty()) {
                tail = convertTransformations(lastStage);
            }
            if (rootStage != null) {
                this.lastStage.setDefaultNext(tail);
            } else {
                rootStage = tail;
            }
        }

        @Override
        public Stage build(Stage stage) {
            addTailStage(stage);

            return rootStage;
        }

        @Override
        public Stage build() {
            return build(null);
        }

        private Stage convertTransformations(Stage successor) {
            Stage stage;
            if (successor == null) {
                stage = new LinkedStage(transformations.poll());
            } else {
                stage = new LinkedStage(transformations.poll(), successor);
            }

            Function t;
            while ((t = transformations.poll()) != null) {
                stage = new LinkedStage(t, stage);
            }

            return stage;
        }
    }

    /**
     * Linked linear stage implementation.
     *
     * @param  processed data type.
     */
    public static class LinkedStage implements Stage {

        private final Stage nextStage;
        private final Function transformation;

        /**
         * Create a new stage that will return the supplied stage in the
         * continuation.
         *
         * @param transformation Request transformation function to be applied in the stage.
         * @param nextStage      next stage returned in the continuation.
         */
        public LinkedStage(Function transformation, Stage nextStage) {
            this.nextStage = nextStage;
            this.transformation = transformation;
        }

        /**
         * Create a new terminal stage .
         *
         * @param transformation Request transformation function to be applied in the stage.
         */
        public LinkedStage(Function transformation) {
            this(transformation, null);
        }

        @Override
        public Stage.Continuation apply(DATA data) {
            return Continuation.of(transformation.apply(data), nextStage);
        }
    }
}