Java tutorial
/** * Licensed to the Hummingbird Foundation (HF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The HF 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.hbird.business.archive.dao.mongo; import java.util.HashMap; import java.util.HashSet; import java.util.List; import java.util.Map; import java.util.Set; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import org.springframework.data.mongodb.MongoDbFactory; import org.springframework.data.mongodb.core.MongoTemplate; import org.springframework.data.mongodb.core.SimpleMongoDbFactory; import org.springframework.data.mongodb.core.convert.MongoConverter; import org.springframework.data.mongodb.core.query.Query; import com.mongodb.BasicDBObject; import com.mongodb.DBCollection; import com.mongodb.DBCursor; import com.mongodb.DBObject; import com.mongodb.Mongo; import com.mongodb.WriteConcern; // TODO: Maybe just querying the hierarchy each time is better if we are going to // fetch the version from DB anyways public class SubclassAwareMongoTemplate extends MongoTemplate { private static final Logger LOG = LoggerFactory.getLogger(SubclassAwareMongoTemplate.class); private static final String HIERARCHY_COLLECTION_NAME = "hbird_hierarchy"; private static final String SUBCLASS_FIELD = "subclass"; private static final String SUPERCLASS_FIELD = "superclass"; private static final String METADATA_COLLECTION_NAME = "hbird_hierarchy_metadata"; private static final String METADATA_VERSION_FIELD = "version"; private DBCollection hierarchy; private DBCollection metadata; private Set<String> knownClasses; private Map<String, Set<String>> subclassRelation; private Map<String, Class<?>> classloaderCache; private long version = 0; public SubclassAwareMongoTemplate(MongoDbFactory dbFactory, MongoConverter mongoConverter) { super(dbFactory, mongoConverter); setWriteConcern(WriteConcern.ACKNOWLEDGED); hierarchy = super.getCollection(HIERARCHY_COLLECTION_NAME); metadata = super.getCollection(METADATA_COLLECTION_NAME); knownClasses = new HashSet<String>(); subclassRelation = new HashMap<String, Set<String>>(); classloaderCache = new HashMap<String, Class<?>>(); LOG.info("Initializing"); if (metadata.count() == 0) { LOG.info("Metadata collection is empty, creating version marker"); writeVersionToDB(); } else { LOG.info("Version marker found"); updateCacheFromDB(); LOG.info("Hierarchy version: " + version); } } public SubclassAwareMongoTemplate(Mongo mongo, String databaseName) { this(new SimpleMongoDbFactory(mongo, databaseName), null); } private void writeVersionToDB() { version = System.currentTimeMillis(); metadata.save(new BasicDBObject("_id", METADATA_VERSION_FIELD).append(METADATA_VERSION_FIELD, version)); } private void updateCacheFromDB() { LOG.trace("Updating hierarchy from DB, local version is {}", version); DBObject versionDoc = metadata.findOne(); LOG.trace("DB version marker object: {}", versionDoc); // Extra check in case the metadata collection is dropped after the construction long dbVersion = versionDoc == null ? 0 : (Long) versionDoc.get(METADATA_VERSION_FIELD); LOG.trace("DB version: {}", dbVersion); if (dbVersion == version) { return; } DBCursor cursor = hierarchy.find(); for (DBObject obj : cursor) { String subclass = (String) obj.get(SUBCLASS_FIELD); String superclass = (String) obj.get(SUPERCLASS_FIELD); if (!knownClasses.contains(subclass)) { try { addToRelationCache(Class.forName(subclass), superclass); knownClasses.add(subclass); } catch (ClassNotFoundException e) { LOG.error("Failed to resolve hierarchy class by name: ", e); } } } version = dbVersion; } private void addToRelationCache(Class<?> subclass, String superclass) { String subName = subclass.getName(); classloaderCache.put(subName, subclass); if (!subclassRelation.containsKey(superclass)) { Set<String> subclasses = new HashSet<String>(); subclasses.add(subName); subclassRelation.put(superclass, subclasses); } else { subclassRelation.get(superclass).add(subName); } } private void saveRelation(Class<?> subclass, String superclass) { BasicDBObject object = new BasicDBObject(SUBCLASS_FIELD, subclass.getName()); object.append(SUPERCLASS_FIELD, superclass); hierarchy.insert(object); addToRelationCache(subclass, superclass); } private void saveIntoHierarchy(Class<?> clazz) { if (!subclassRelation.containsKey(clazz.getName())) { subclassRelation.put(clazz.getName(), new HashSet<String>()); } if (knownClasses.contains(clazz.getName())) { return; } Class<?> sup = clazz.getSuperclass(); while (sup != null) { saveRelation(clazz, sup.getName()); saveIntoHierarchy(sup); writeVersionToDB(); sup = sup.getSuperclass(); } knownClasses.add(clazz.getName()); } private void addToHierarchy(Class<?> clazz) { updateCacheFromDB(); saveIntoHierarchy(clazz); } @Override public <T> T findOne(Query query, Class<T> clazz) { addToHierarchy(clazz); T result = super.findOne(query, clazz); if (result != null) { return result; } for (String subclassName : subclassRelation.get(clazz.getName())) { Class<? extends T> subclass = (Class<? extends T>) classloaderCache.get(subclassName); result = super.findOne(query, subclass); if (result != null) { return result; } } return null; } @Override public <T> List<T> find(Query query, Class<T> clazz) { addToHierarchy(clazz); List<T> result = super.find(query, clazz); assert subclassRelation.containsKey(clazz.getName()); assert subclassRelation.get(clazz.getName()) != null; for (String subclassName : subclassRelation.get(clazz.getName())) { Class<? extends T> subclass = (Class<? extends T>) classloaderCache.get(subclassName); result.addAll(super.find(query, subclass)); } return result; } @Override public <T> List<T> findAll(Class<T> clazz) { addToHierarchy(clazz); List<T> result = super.findAll(clazz); for (String subclassName : subclassRelation.get(clazz.getName())) { Class<? extends T> subclass = (Class<? extends T>) classloaderCache.get(subclassName); result.addAll(super.findAll(subclass)); } return result; } public void save(Object toSave) { addToHierarchy(toSave.getClass()); super.save(toSave); } }