Java tutorial
/* * Copyright (c) 2014. Escalon System-Entwicklung, Dietrich Schulten * * 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 de.escalon.hypermedia.spring.hydra; import com.fasterxml.jackson.core.JsonGenerator; import com.fasterxml.jackson.databind.JavaType; import com.fasterxml.jackson.databind.JsonSerializer; import com.fasterxml.jackson.databind.SerializationConfig; import com.fasterxml.jackson.databind.SerializerProvider; import com.fasterxml.jackson.databind.ser.BeanSerializerFactory; import com.fasterxml.jackson.databind.ser.std.StdSerializer; import com.fasterxml.jackson.databind.util.NameTransformer; import de.escalon.hypermedia.hydra.serialize.*; import org.springframework.hateoas.Link; import org.springframework.hateoas.PagedResources; import java.io.IOException; import java.util.*; import static de.escalon.hypermedia.hydra.serialize.JacksonHydraSerializer.KEY_LD_CONTEXT; /** * Serializer for Resources. Created by dschulten on 15.09.2014. */ @SuppressWarnings("unused") public class PagedResourcesSerializer extends StdSerializer<PagedResources> { private final static Set<String> navigationRels = new HashSet<String>(); static { Collections.addAll(navigationRels, Link.REL_FIRST, Link.REL_NEXT, Link.REL_PREVIOUS, Link.REL_LAST); } private final LdContextFactory ldContextFactory; private final ProxyUnwrapper proxyUnwrapper; @SuppressWarnings("unused") public PagedResourcesSerializer(ProxyUnwrapper proxyUnwrapper) { super(PagedResources.class); this.ldContextFactory = new LdContextFactory(); this.proxyUnwrapper = proxyUnwrapper; ldContextFactory.setProxyUnwrapper(proxyUnwrapper); } @Override public void serialize(PagedResources pagedResources, JsonGenerator jgen, SerializerProvider serializerProvider) throws IOException { final SerializationConfig config = serializerProvider.getConfig(); JavaType javaType = config.constructType(pagedResources.getClass()); JsonSerializer<Object> serializer = BeanSerializerFactory.instance.createSerializer(serializerProvider, javaType); // replicate pretty much everything from JacksonHydraSerializer // since we must reorganize the internals of pagedResources to get a hydra collection // with partial page view, we have to serialize pagedResources with an // unwrapping serializer Deque<LdContext> contextStack = (Deque<LdContext>) serializerProvider.getAttribute(KEY_LD_CONTEXT); if (contextStack == null) { contextStack = new ArrayDeque<LdContext>(); serializerProvider.setAttribute(KEY_LD_CONTEXT, contextStack); } // TODO: filter next/previous/first/last from link list - maybe create new PagedResources without them? List<Link> links = pagedResources.getLinks(); List<Link> filteredLinks = new ArrayList<Link>(); for (Link link : links) { String rel = link.getRel(); if (navigationRels.contains(rel)) { continue; } else { filteredLinks.add(link); } } PagedResources toRender = new PagedResources(pagedResources.getContent(), pagedResources.getMetadata(), filteredLinks); jgen.writeStartObject(); serializeContext(toRender, jgen, serializerProvider, contextStack); jgen.writeStringField(JsonLdKeywords.AT_TYPE, "hydra:Collection"); // serialize with PagedResourcesMixin serializer.unwrappingSerializer(NameTransformer.NOP).serialize(toRender, jgen, serializerProvider); PagedResources.PageMetadata metadata = pagedResources.getMetadata(); jgen.writeNumberField("hydra:totalItems", metadata.getTotalElements()); // begin hydra:view jgen.writeObjectFieldStart("hydra:view"); jgen.writeStringField(JsonLdKeywords.AT_TYPE, "hydra:PartialCollectionView"); writeRelLink(pagedResources, jgen, Link.REL_NEXT); writeRelLink(pagedResources, jgen, "previous"); // must also translate prev to its synonym previous writeRelLink(pagedResources, jgen, Link.REL_PREVIOUS, "previous"); writeRelLink(pagedResources, jgen, Link.REL_FIRST); writeRelLink(pagedResources, jgen, Link.REL_LAST); jgen.writeEndObject(); // end hydra:view jgen.writeEndObject(); contextStack = (Deque<LdContext>) serializerProvider.getAttribute(KEY_LD_CONTEXT); if (!contextStack.isEmpty()) { contextStack.pop(); } } protected void serializeContext(Object bean, JsonGenerator jgen, SerializerProvider serializerProvider, Deque<LdContext> contextStack) throws IOException { // TODO: this code is duplicated from JacksonHydraSerializer, see there for considerations if (proxyUnwrapper != null) { bean = proxyUnwrapper.unwrapProxy(bean); } MixinSource mixinSource = new JacksonMixinSource(serializerProvider.getConfig()); final Class<?> mixInClass = mixinSource.findMixInClassFor(bean.getClass()); final LdContext parentContext = contextStack.peek(); LdContext currentContext = new LdContext(parentContext, ldContextFactory.getVocab(mixinSource, bean, mixInClass), ldContextFactory.getTerms(mixinSource, bean, mixInClass)); contextStack.push(currentContext); // check if we need to write a context for the current bean at all // If it is in the same vocab: no context // If the terms are already defined in the context: no context boolean mustWriteContext; if (parentContext == null || !parentContext.contains(currentContext)) { mustWriteContext = true; } else { mustWriteContext = false; } if (mustWriteContext) { // begin context // default context: schema.org vocab or vocab package annotation jgen.writeObjectFieldStart("@context"); // do not repeat vocab if already defined in current context if (parentContext == null || parentContext.vocab == null || (currentContext.vocab != null && !currentContext.vocab.equals(parentContext.vocab))) { jgen.writeStringField(JsonLdKeywords.AT_VOCAB, currentContext.vocab); } for (Map.Entry<String, Object> termEntry : currentContext.terms.entrySet()) { if (termEntry.getValue() instanceof String) { jgen.writeStringField(termEntry.getKey(), termEntry.getValue().toString()); } else { jgen.writeObjectField(termEntry.getKey(), termEntry.getValue()); } } jgen.writeEndObject(); // end context } } private void writeRelLink(PagedResources value, JsonGenerator jgen, String rel) throws IOException { writeRelLink(value, jgen, rel, rel); } private void writeRelLink(PagedResources value, JsonGenerator jgen, String rel, String hydraPredicate) throws IOException { Link link = value.getLink(rel); if (link != null) { jgen.writeStringField("hydra:" + hydraPredicate, link.getHref()); } } }