1 package org.apache.onami.persist; 2 3 /* 4 * Licensed to the Apache Software Foundation (ASF) under one 5 * or more contributor license agreements. See the NOTICE file 6 * distributed with this work for additional information 7 * regarding copyright ownership. The ASF licenses this file 8 * to you under the Apache License, Version 2.0 (the 9 * "License"); you may not use this file except in compliance 10 * with the License. You may obtain a copy of the License at 11 * 12 * http://www.apache.org/licenses/LICENSE-2.0 13 * 14 * Unless required by applicable law or agreed to in writing, 15 * software distributed under the License is distributed on an 16 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY 17 * KIND, either express or implied. See the License for the 18 * specific language governing permissions and limitations 19 * under the License. 20 */ 21 22 import javax.persistence.EntityManager; 23 24 /** 25 * The Unit of work correlates with the life cycle of the {@link EntityManager}. 26 * According to JPA every thread should use its own {@link EntityManager}. Therefore the unit of 27 * work will control the life cycle of the {@link EntityManager} on a per thread basis. This means 28 * the UnitOfWork is thread safe. 29 * <p/> 30 * Most of the time it is not recommended to manual control the unit of work. 31 * <p/> 32 * For applications running in a container the {@link PersistenceFilter} is recommended. 33 * It will start a unit of work for every incoming request and properly close it at the end. 34 * <p/> 35 * For stand alone application it is recommended to relay on the {@link Transactional @Transactional} annotation. 36 * The transaction handler will automatically span a unit of work around a transaction. 37 * <p/> 38 * The most likely scenario in which one would want to take manual control over the unit of work 39 * is in a background thread within a container (i.e. timer triggered jobs). 40 * <p/> 41 * Recommended pattern: 42 * <pre> 43 * public void someMethod() { 44 * final boolean unitOfWorkWasInactive = ! unitOfWork.isActive(); 45 * if (unitOfWorkWasInactive) { 46 * unitOfWork.begin(); 47 * } 48 * try { 49 * // do work 50 * } 51 * finally { 52 * if (unitOfWorkWasInactive) { 53 * unitOfWork.end(); 54 * } 55 * } 56 * } 57 * </pre> 58 */ 59 public interface UnitOfWork 60 { 61 62 /** 63 * Begins the unit of work. 64 * When a unit of work has already been started for the current thread an {@link IllegalStateException} is thrown. 65 * 66 * @throws IllegalStateException if a unit of work is already active for this thread. 67 */ 68 void begin(); 69 70 /** 71 * @return {@code true} if the unit of work is active for the current thread 72 * {@code false} otherwise. 73 */ 74 boolean isActive(); 75 76 /** 77 * Ends the unit of work. 78 * When the unit of work is not active this method will do nothing. 79 */ 80 void end(); 81 82 }