org.springframework.restdocs.hypermedia.LinkExtractors.java Source code

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Here is the source code for org.springframework.restdocs.hypermedia.LinkExtractors.java

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/*
 * Copyright 2014-2015 the original author or authors.
 *
 * 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.springframework.restdocs.hypermedia;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;

import org.springframework.http.MediaType;
import org.springframework.mock.web.MockHttpServletResponse;

import com.fasterxml.jackson.databind.ObjectMapper;

/**
 * Static factory methods providing a selection of {@link LinkExtractor link extractors}
 * for use when documentating a hypermedia-based API.
 *
 * @author Andy Wilkinson
 */
public abstract class LinkExtractors {

    private LinkExtractors() {

    }

    /**
     * Returns a {@code LinkExtractor} capable of extracting links in Hypermedia
     * Application Language (HAL) format where the links are found in a map named
     * {@code _links}.
     *
     * @return The extract for HAL-style links
     */
    public static LinkExtractor halLinks() {
        return new HalLinkExtractor();
    }

    /**
     * Returns a {@code LinkExtractor} capable of extracting links in Atom format where
     * the links are found in an array named {@code links}.
     *
     * @return The extractor for Atom-style links
     */
    public static LinkExtractor atomLinks() {
        return new AtomLinkExtractor();
    }

    /**
     * Returns the {@code LinkExtractor} for the given {@code contentType} or {@code null}
     * if there is no extractor for the content type.
     * 
     * @param contentType The content type
     * @return The extractor for the content type, or {@code null}
     */
    public static LinkExtractor extractorForContentType(String contentType) {
        if (MediaType.APPLICATION_JSON_VALUE.equals(contentType)) {
            return atomLinks();
        } else if ("application/hal+json".equals(contentType)) {
            return halLinks();
        }
        return null;
    }

    private abstract static class JsonContentLinkExtractor implements LinkExtractor {

        private final ObjectMapper objectMapper = new ObjectMapper();

        @Override
        @SuppressWarnings("unchecked")
        public Map<String, List<Link>> extractLinks(MockHttpServletResponse response) throws IOException {
            Map<String, Object> jsonContent = this.objectMapper.readValue(response.getContentAsString(), Map.class);
            return extractLinks(jsonContent);
        }

        protected abstract Map<String, List<Link>> extractLinks(Map<String, Object> json);
    }

    @SuppressWarnings("unchecked")
    private static class HalLinkExtractor extends JsonContentLinkExtractor {

        @Override
        public Map<String, List<Link>> extractLinks(Map<String, Object> json) {
            Map<String, List<Link>> extractedLinks = new HashMap<>();
            Object possibleLinks = json.get("_links");
            if (possibleLinks instanceof Map) {
                Map<String, Object> links = (Map<String, Object>) possibleLinks;
                for (Entry<String, Object> entry : links.entrySet()) {
                    String rel = entry.getKey();
                    extractedLinks.put(rel, convertToLinks(entry.getValue(), rel));
                }
            }
            return extractedLinks;
        }

        private static List<Link> convertToLinks(Object object, String rel) {
            List<Link> links = new ArrayList<>();
            if (object instanceof Collection) {
                Collection<Object> hrefObjects = (Collection<Object>) object;
                for (Object hrefObject : hrefObjects) {
                    maybeAddLink(maybeCreateLink(rel, hrefObject), links);
                }
            } else {
                maybeAddLink(maybeCreateLink(rel, object), links);
            }
            return links;
        }

        private static Link maybeCreateLink(String rel, Object possibleHref) {
            if (possibleHref instanceof String) {
                return new Link(rel, (String) possibleHref);
            }
            return null;
        }

        private static void maybeAddLink(Link possibleLink, List<Link> links) {
            if (possibleLink != null) {
                links.add(possibleLink);
            }
        }
    }

    @SuppressWarnings("unchecked")
    private static class AtomLinkExtractor extends JsonContentLinkExtractor {

        @Override
        public Map<String, List<Link>> extractLinks(Map<String, Object> json) {
            Map<String, List<Link>> extractedLinks = new HashMap<>();
            Object possibleLinks = json.get("links");
            if (possibleLinks instanceof Collection) {
                Collection<Object> linksCollection = (Collection<Object>) possibleLinks;
                for (Object linkObject : linksCollection) {
                    if (linkObject instanceof Map) {
                        Link link = maybeCreateLink((Map<String, Object>) linkObject);
                        maybeStoreLink(link, extractedLinks);
                    }
                }
            }
            return extractedLinks;
        }

        private static Link maybeCreateLink(Map<String, Object> linkMap) {
            Object hrefObject = linkMap.get("href");
            Object relObject = linkMap.get("rel");
            if (relObject instanceof String && hrefObject instanceof String) {
                return new Link((String) relObject, (String) hrefObject);
            }
            return null;
        }

        private static void maybeStoreLink(Link link, Map<String, List<Link>> extractedLinks) {
            if (link != null) {
                List<Link> linksForRel = extractedLinks.get(link.getRel());
                if (linksForRel == null) {
                    linksForRel = new ArrayList<Link>();
                    extractedLinks.put(link.getRel(), linksForRel);
                }
                linksForRel.add(link);
            }
        }
    }
}