Java tutorial
/* * Copyright 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.data.mongodb.core.convert; import static org.springframework.data.mongodb.util.MongoClientVersion.*; import static org.springframework.util.ReflectionUtils.*; import java.lang.reflect.Method; import org.springframework.data.mongodb.MongoDbFactory; import org.springframework.util.Assert; import com.mongodb.DBCollection; import com.mongodb.DBObject; import com.mongodb.DBRef; /** * {@link ReflectiveDBRefResolver} provides reflective access to {@link DBRef} API that is not consistently available * for various driver versions. * * @author Christoph Strobl * @author Oliver Gierke * @since 1.7 */ class ReflectiveDBRefResolver { private static final Method FETCH_METHOD; static { FETCH_METHOD = findMethod(DBRef.class, "fetch"); } /** * Fetches the object referenced from the database either be directly calling {@link DBRef#fetch()} or * {@link DBCollection#findOne(Object)}. * * @param db can be {@literal null} when using MongoDB Java driver in version 2.x. * @param ref must not be {@literal null}. * @return the document that this references. */ public static DBObject fetch(MongoDbFactory factory, DBRef ref) { Assert.notNull(ref, "DBRef to fetch must not be null!"); if (isMongo3Driver()) { Assert.notNull(factory, "DbFactory to fetch DB from must not be null!"); return factory.getDb().getCollection(ref.getCollectionName()).findOne(ref.getId()); } return (DBObject) invokeMethod(FETCH_METHOD, ref); } }