Hibernate实战(第二版)笔记----第三章--域模型与元数据

今天药忘吃喽~ 2022-06-13 09:12 249阅读 0赞

本章主要讲了域模型和元数据,以一个CaveatEmptor在线拍卖系统为例讲解了从项目架构分层,分析业务域,域模型,域模型的持久化类和持久化层之间的关注点完全分离,持久化类不清楚-且不依赖-持久化机制,然后讲解了域模型域元数据的关系,以及在运行时的方法方式。  
  
域模型:被创建的实体类与属性被称为域模型.

元数据:即告知Hibernate持久化类及其属性与数据库表和列关联起来的方式。

JPA提供了两个元数据选项:

1、注解

2、XML描述符

JPA提供的访问持久化元模型API:

1、JAVA持久化中的动态元模型API

2、使用一个静态元模型

CaveatEmptor示例

CaveatEmptor是一个揭示ORM技术和Hibernate功能的在线拍卖应用,其中域模型为:

![20170703220612026][]

所对应的实体类为:

![20170703222034505][]

/model/src/main/java/org/jpwh/model/simple/Item.java

package org.jpwh.model.simple;
    
    import javax.persistence.Entity;
    
    import javax.persistence.FetchType;
    import javax.persistence.GeneratedValue;
    import javax.persistence.Id;
    import javax.persistence.ManyToOne;
    import javax.persistence.Transient;
    import javax.persistence.Version;
    import javax.validation.constraints.Future;
    import javax.validation.constraints.NotNull;
    import javax.validation.constraints.Size;
    
    import java.math.BigDecimal;
    import java.util.Date;
    import java.util.HashSet;
    import java.util.Set;
    
    @Entity
    public class Item {
    
        @Id
        @GeneratedValue(generator = "ID_GENERATOR")
        protected Long id;
    
        public Long getId() { // 可选但有用
            return id;
        }
    
        @Version
        protected long version;
    
        @NotNull
        @Size(
            min = 2,
            max = 255,
            message = "Name is required, maximum 255 characters."
        )
        protected String name;
    
        @Future
        protected Date auctionEnd;
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public Date getAuctionEnd() {
            return auctionEnd;
        }
    
        public void setAuctionEnd(Date auctionEnd) {
            this.auctionEnd = auctionEnd;
        }
    
        protected BigDecimal buyNowPrice;
    
        public BigDecimal getBuyNowPrice() {
            return buyNowPrice;
        }
    
        public void setBuyNowPrice(BigDecimal buyNowPrice) {
            this.buyNowPrice = buyNowPrice;
        }
    
        @Transient
        protected Set<Bid> bids = new HashSet<Bid>();
    
        public Set<Bid> getBids() {
            return bids;
        }
    
        public void setBids(Set<Bid> bids) {
            this.bids = bids;
        }
    
        @ManyToOne(fetch = FetchType.LAZY)
        protected Category category;
    
        public Category getCategory() {
            return category;
        }
    
        public void setCategory(Category category) {
            this.category = category;
        }
    
        public void addBid(Bid bid) {
            // Be defensive
            if (bid == null)
                throw new NullPointerException("Can't add null Bid");
            if (bid.getItem() != null)
                throw new IllegalStateException("Bid is already assigned to an Item");
    
            getBids().add(bid);
            bid.setItem(this);
        }
    
        public Bid placeBid(Bid currentHighestBid, BigDecimal bidAmount) {
            if (currentHighestBid == null ||
                    bidAmount.compareTo(currentHighestBid.getAmount()) > 0) {
                return new Bid(bidAmount, this);
            }
            return null;
        }
    }

/model/src/main/java/org/jpwh/model/simple/Item\_.java

package org.jpwh.model.simple;
    
    import java.util.Date;
    
    import javax.persistence.metamodel.SingularAttribute;
    
    @javax.persistence.metamodel.StaticMetamodel(Item.class)
    public abstract class Item_ {
    
        public static volatile SingularAttribute<Item,Long> id;
    	public static volatile SingularAttribute<Item,String> name;
    	public static volatile SingularAttribute<Item,Date> auctionEnd;
    }

/model/src/main/java/org/jpwh/model/simple/Bid.java

package org.jpwh.model.simple;
    
    import org.jpwh.model.Constants;
    
    import javax.persistence.Entity;
    import javax.persistence.FetchType;
    import javax.persistence.GeneratedValue;
    import javax.persistence.Id;
    import javax.persistence.JoinColumn;
    import javax.persistence.ManyToOne;
    import javax.validation.constraints.NotNull;
    import java.math.BigDecimal;
    
    @Entity
    public class Bid {
    
        @Id
        @GeneratedValue(generator = Constants.ID_GENERATOR)
        protected Long id;
    
        public Long getId() { // 可选的但是有用的
            return id;
        }
    
        public Bid() {
        }
    
        @NotNull
        protected BigDecimal amount;
    
        public Bid(BigDecimal amount, Item item) {
            this.amount = amount;
            this.item = item;
        }
    
        public BigDecimal getAmount() {
            return amount;
        }
    
        public void setAmount(BigDecimal amount) {
            this.amount = amount;
        }
    
        @ManyToOne(optional = false, fetch = FetchType.LAZY) // NOT NULL
        @JoinColumn(name = "ITEM_ID") // 实际上默认名称
        protected Item item;
    
        public Bid(Item item) {
            this.item = item;
            item.getBids().add(this); // 双向
        }
    
        public Item getItem() {
            return item;
        }
    
        public void setItem(Item item) {
            this.item = item;
        }
    }

/model/src/main/java/org/jpwh/model/simple/Address.java

package org.jpwh.model.simple;
    
    import javax.persistence.Column;
    import javax.persistence.Embeddable;
    import javax.validation.constraints.NotNull;
    
    /**
     * 
     *而不是<code> @Entity </code>，该组件POJO标有<code> @Embeddable </code>。 它
     *没有标识符属性。
     */
    @Embeddable
    public class Address {
    
        @NotNull // 忽略了DDL生成！
        @Column(nullable = false) // 用于DDL生成！
        protected String street;
    
        @NotNull
        @Column(nullable = false, length = 5) // Override VARCHAR(255)
        protected String zipcode;
    
        @NotNull
        @Column(nullable = false)
        protected String city;
    
        /**
         *Hibernate会调用这个无参数的构造函数来创建一个实例，然后
         *直接填充字段。
         */
        protected Address() {
        }
    
        /**
         *为方便起见，您可以拥有其他(public)构造函数。     
         **/
        public Address(String street, String zipcode, String city) {
            this.street = street;
            this.zipcode = zipcode;
            this.city = city;
        }
    
        public String getStreet() {
            return street;
        }
    
        public void setStreet(String street) {
            this.street = street;
        }
    
        public String getZipcode() {
            return zipcode;
        }
    
        public void setZipcode(String zipcode) {
            this.zipcode = zipcode;
        }
    
        public String getCity() {
            return city;
        }
    
        public void setCity(String city) {
            this.city = city;
        }
    }

/model/src/main/java/org/jpwh/model/simple/Category.java

package org.jpwh.model.simple;
    
    import org.jpwh.model.Constants;
    
    import javax.persistence.Entity;
    import javax.persistence.GeneratedValue;
    import javax.persistence.Id;
    
    @Entity
    public class Category {
    
        @Id
        @GeneratedValue(generator = Constants.ID_GENERATOR)
        protected Long id;
    
        public Long getId() {
            return id;
        }
    
        protected String name;
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
    }

提供的一些测试类:

![20170703222508104][]

/examples/src/test/java/org/jpwh/test/simple/AccessJPAMetamodel.java

package org.jpwh.test.simple;
    
    import org.jpwh.env.JPATest;
    import org.jpwh.model.simple.Item;
    import org.jpwh.model.simple.Item_;
    import org.testng.annotations.Test;
    
    import javax.persistence.EntityManager;
    import javax.persistence.EntityManagerFactory;
    import javax.persistence.criteria.CriteriaBuilder;
    import javax.persistence.criteria.CriteriaQuery;
    import javax.persistence.criteria.Path;
    import javax.persistence.criteria.Root;
    import javax.persistence.metamodel.Attribute;
    import javax.persistence.metamodel.ManagedType;
    import javax.persistence.metamodel.Metamodel;
    import javax.persistence.metamodel.SingularAttribute;
    import javax.persistence.metamodel.Type;
    import javax.transaction.UserTransaction;
    import java.util.Date;
    import java.util.List;
    import java.util.Set;
    
    import static org.testng.Assert.assertEquals;
    import static org.testng.Assert.assertFalse;
    
    //JPA访问元模型
    public class AccessJPAMetamodel extends JPATest {
    
        @Override
        public void configurePersistenceUnit() throws Exception {
            configurePersistenceUnit("SimpleXMLCompletePU");
        }
    
        @Test
        public void accessDynamicMetamodel() throws Exception {
            EntityManagerFactory entityManagerFactory = JPA.getEntityManagerFactory();
    
            Metamodel mm = entityManagerFactory.getMetamodel();
    
            Set<ManagedType<?>> managedTypes = mm.getManagedTypes();
            assertEquals(managedTypes.size(), 1);
    
            ManagedType itemType = managedTypes.iterator().next();
            assertEquals(
                itemType.getPersistenceType(),
                Type.PersistenceType.ENTITY
            );
    
            SingularAttribute nameAttribute =
                itemType.getSingularAttribute("name");
            assertEquals(
                nameAttribute.getJavaType(),
                String.class
            );
            assertEquals(
                nameAttribute.getPersistentAttributeType(),
                Attribute.PersistentAttributeType.BASIC
            );
            assertFalse(
                nameAttribute.isOptional() // NOT NULL
            );
    
            SingularAttribute auctionEndAttribute =
                itemType.getSingularAttribute("auctionEnd");
            assertEquals(
                auctionEndAttribute.getJavaType(),
                Date.class
            );
            assertFalse(
                auctionEndAttribute.isCollection()
            );
            assertFalse(
                auctionEndAttribute.isAssociation()
            );
        }
    
        @Test
        public void accessStaticMetamodel() throws Exception {
    
            SingularAttribute nameAttribute = Item_.name;
    
            assertEquals(
                nameAttribute.getJavaType(),
                String.class
            );
        }
    
        @Test
        public void queryStaticMetamodel() throws Exception {
            UserTransaction tx = TM.getUserTransaction();
            try {
                tx.begin();
    
                EntityManager entityManager = JPA.createEntityManager();
    
                Item itemOne = new Item();
                itemOne.setName("This is some item");
                itemOne.setAuctionEnd(new Date(System.currentTimeMillis() + 100000));
                entityManager.persist(itemOne);
    
                Item itemTwo = new Item();
                itemTwo.setName("Another item");
                itemTwo.setAuctionEnd(new Date(System.currentTimeMillis() + 100000));
    
                entityManager.persist(itemTwo);
    
                tx.commit();
                entityManager.close();
    
                entityManager = JPA.createEntityManager();
                tx.begin();
    
                CriteriaBuilder cb = entityManager.getCriteriaBuilder();
    
                // This query is the equivalent of "select i from Item i"
                CriteriaQuery<Item> query = cb.createQuery(Item.class);
                Root<Item> fromItem = query.from(Item.class);
                query.select(fromItem);
    
                List<Item> items =
                    entityManager.createQuery(query)
                        .getResultList();
    
                assertEquals(items.size(), 2);
    
                // "where i.name like :pattern"
                Path<String> namePath = fromItem.get("name");
                query.where(
                    cb.like(
                        namePath, // Has to be a Path<String> for like() operator!
                        cb.parameter(String.class, "pattern")
                    )
                );
    
                items =
                    entityManager.createQuery(query)
                        .setParameter("pattern", "%some item%") // Wildcards!
                        .getResultList();
    
                assertEquals(items.size(), 1);
                assertEquals(items.iterator().next().getName(), "This is some item");
    
                query.where(
                    cb.like(
                        fromItem.get(Item_.name), // Static Item_ metamodel!
                        cb.parameter(String.class, "pattern")
                    )
                );
    
                items =
                    entityManager.createQuery(query)
                        .setParameter("pattern", "%some item%") // Wildcard!
                        .getResultList();
    
                assertEquals(items.size(), 1);
                assertEquals(items.iterator().next().getName(), "This is some item");
    
                tx.commit();
                entityManager.close();
            } finally {
                TM.rollback();
            }
        }
    
    }

/examples/src/test/java/org/jpwh/test/simple/CRUD.java

package org.jpwh.test.simple;
    
    import org.jpwh.env.JPATest;
    import org.jpwh.model.simple.Item;
    import org.testng.annotations.BeforeClass;
    import org.testng.annotations.Test;
    
    import javax.persistence.EntityManager;
    import javax.persistence.Query;
    import javax.transaction.UserTransaction;
    import java.util.Date;
    import java.util.List;
    
    import static org.testng.Assert.assertEquals;
    
    public class CRUD extends JPATest {
    
        @Override
        public void configurePersistenceUnit() throws Exception {
            configurePersistenceUnit("SimplePU");
        }
    
        @Test
        public void storeAndQueryItems() throws Exception {
            storeAndQueryItems("findItems");
        }
    
        public void storeAndQueryItems(String queryName) throws Exception {
            UserTransaction tx = TM.getUserTransaction();
            try {
                tx.begin();
                EntityManager em = JPA.createEntityManager();
    
                Item itemOne = new Item();
                itemOne.setName("Item One");
                itemOne.setAuctionEnd(new Date(System.currentTimeMillis() + 100000));
                em.persist(itemOne);
    
                Item itemTwo = new Item();
                itemTwo.setName("Item Two");
                itemTwo.setAuctionEnd(new Date(System.currentTimeMillis() + 100000));
    
                em.persist(itemTwo);
    
                tx.commit();
                em.close();
    
                tx.begin();
                em = JPA.createEntityManager();
    
                Query q = em.createNamedQuery(queryName);
                List<Item> items = q.getResultList();
    
                assertEquals(items.size(), 2);
    
                tx.commit();
                em.close();
            } finally {
                TM.rollback();
            }
        }
    
    }

/examples/src/test/java/org/jpwh/test/simple/CRUDMetadataHBMXML.java

package org.jpwh.test.simple;
    
    import org.testng.annotations.Test;
    
    //CRUD HBM XML元数据
    public class CRUDMetadataHBMXML extends CRUD {
    
        @Override
        public void configurePersistenceUnit() throws Exception {
            configurePersistenceUnit("SimpleXMLHibernatePU", "simple/Native.hbm.xml");
        }
    
        @Test
        @Override
        public void storeAndQueryItems() throws Exception {
            super.storeAndQueryItems("findItemsHibernate");
        }
    }

/examples/src/test/java/org/jpwh/test/simple/CRUDMetadataOverrideXML.java

package org.jpwh.test.simple;
    
    import org.hibernate.SessionFactory;
    import org.testng.annotations.BeforeClass;
    import org.testng.annotations.Test;
    
    //CRUD XML元数据覆盖
    public class CRUDMetadataOverrideXML extends CRUD {
    
        @Override
        public void configurePersistenceUnit() throws Exception {
            configurePersistenceUnit("SimpleXMLOverridePU");
        }
    
        @Test
        @Override
        public void storeAndQueryItems() throws Exception {
            super.storeAndQueryItems();
        }
    
        @Test
        public void checkMetadataOverride() throws Exception {
        	
        	//使用Hibernate元数据API来查找覆盖SQL列的名称，JPA不
    	    //支持访问SQL详细信息
    	    // TODO：不知道如何使用Hibernate 5 API访问SQL映射详细信息...
        	
            /*
            Property nameProperty = itemClass.getProperty("name");
            Column nameColumn = (Column) nameProperty.getColumnIterator().next();
    
            // 列的名称来自XML描述符
            assertEquals(nameColumn.getName(), "ITEM_NAME");
    
            // 但是Bean验证注释仍然被识别！
            assertEquals(nameColumn.isNullable(), false);
            assertEquals(nameColumn.getLength(), 255);
            */
        }
    }

/examples/src/test/java/org/jpwh/test/simple/CRUDMetadataXML.java

package org.jpwh.test.simple;
    
    import org.testng.annotations.BeforeClass;
    import org.testng.annotations.Test;
    
    //CRUD XML元数据
    public class CRUDMetadataXML extends CRUD {
    
        @Override
        public void configurePersistenceUnit() throws Exception {
            configurePersistenceUnit("SimpleXMLCompletePU");
        }
    
        @Test
        @Override
        public void storeAndQueryItems() throws Exception {
            super.storeAndQueryItems();
        }
    }

/examples/src/test/java/org/jpwh/test/simple/MappingEmbeddables.java

package org.jpwh.test.simple;
    
    import org.jpwh.env.JPATest;
    import org.jpwh.model.simple.Address;
    import org.jpwh.model.simple.User;
    import org.testng.annotations.BeforeClass;
    import org.testng.annotations.Test;
    
    import javax.persistence.EntityManager;
    import javax.persistence.PersistenceException;
    import javax.transaction.UserTransaction;
    
    import java.util.logging.Level;
    import java.util.logging.Logger;
    
    import static org.testng.Assert.assertEquals;
    
    
    //映射可嵌入
    public class MappingEmbeddables extends JPATest {
    
        private static final Logger LOG = Logger.getLogger(MappingEmbeddables.class.getName());
    
        @Override
        public void configurePersistenceUnit() throws Exception {
            configurePersistenceUnit("SimplePU");
        }
    
        @Test
        public void storeAndLoadUsers() throws Exception {
            UserTransaction tx = TM.getUserTransaction();
            try {
                tx.begin();
                EntityManager em = JPA.createEntityManager();
    
                User user = new User();
                user.setUsername("johndoe");
                Address homeAddress = new Address("Some Street 123", "12345", "Some City");
                user.setHomeAddress(homeAddress);
                em.persist(user);
    
                tx.commit();
                em.close();
    
                tx.begin();
                em = JPA.createEntityManager();
    
                User u = em.find(User.class, user.getId());
    
                assertEquals(u.getUsername(), "johndoe");
                assertEquals(u.getHomeAddress().getStreet(), "Some Street 123");
    
                tx.commit();
                em.close();
            } finally {
                TM.rollback();
            }
        }
    
        @Test(expectedExceptions = org.hibernate.exception.ConstraintViolationException.class)
        public void storeAndLoadInvalidUsers() throws Throwable {
            UserTransaction tx = TM.getUserTransaction();
            try {
                tx.begin();
                EntityManager em = JPA.createEntityManager();
    
                User user = new User();
                user.setUsername("johndoe");
                Address homeAddress = new Address("Some Street 123", "12345", null); // NULL city!
                user.setHomeAddress(homeAddress);
                em.persist(user);
    
                try {
                    // Hibernate尝试插入但失败
                    em.flush();
    
                  //注意:如果你尝试用tx.commit()和一个冲洗的副作用，你就不会
                  //得到ConstraintViolationException。Hibernate会在内部捕获它
                  //简单地将事务标记为回滚。
    
                } catch (Exception ex) {
                    throw unwrapCauseOfType(ex, org.hibernate.exception.ConstraintViolationException.class);
                }
            } finally {
                TM.rollback();
            }
        }
    
    }

/examples/src/test/java/org/jpwh/test/simple/MappingManyToOne.java

package org.jpwh.test.simple;
    
    import org.jpwh.env.JPATest;
    import org.jpwh.model.simple.Bid;
    import org.jpwh.model.simple.Item;
    import org.testng.annotations.BeforeClass;
    import org.testng.annotations.Test;
    
    import javax.persistence.EntityManager;
    import javax.transaction.UserTransaction;
    import java.math.BigDecimal;
    
    import static org.testng.Assert.assertEquals;
    
    //映射多对一
    public class MappingManyToOne extends JPATest {
    
        @Override
        public void configurePersistenceUnit() throws Exception {
            configurePersistenceUnit("SimplePU");
        }
    
        @Test
        public void storeAndLoadBids() throws Exception {
            UserTransaction tx = TM.getUserTransaction();
            try {
                tx.begin();
                EntityManager em = JPA.createEntityManager();
    
                //存储在一个持久性上下文（事务）
                Item anItem = new Item();
                anItem.setName("Example Item");
    
                Bid firstBid = new Bid(new BigDecimal("123.00"), anItem);
    
                Bid secondBid = new Bid(new BigDecimal("456.00"), anItem);
    
                // 订单在这里很重要,Hibernate不够聪明了！
                em.persist(anItem);
                em.persist(firstBid);
                em.persist(secondBid);
    
                tx.commit();
                em.close();
    
                tx.begin();
                em = JPA.createEntityManager();
    
                Long BID_ID = firstBid.getId();
    
                // 加载另一个持久性上下文
                Bid someBid = em.find(Bid.class, BID_ID); // SQL SELECT
    
              //初始化Item代理，因为我们调用getId()，它是
              //未映射为标识符属性(the field is!)
                assertEquals(someBid.getItem().getId(), anItem.getId()); // SQL SELECT
    
                tx.commit();
                em.close();
            } finally {
                TM.rollback();
            }
        }
    
    }

/examples/src/test/java/org/jpwh/test/simple/ModelOperations.java

package org.jpwh.test.simple;
    
    import org.jpwh.model.simple.Bid;
    import org.jpwh.model.simple.Item;
    import org.testng.annotations.Test;
    
    import javax.validation.ConstraintViolation;
    import javax.validation.Validation;
    import javax.validation.Validator;
    import javax.validation.ValidatorFactory;
    import java.util.Date;
    import java.util.Locale;
    import java.util.Set;
    
    import static org.testng.Assert.*;
    
    //模式操作
    public class ModelOperations {
    
        @Test
        public void linkBidAndItem() {
            Item anItem = new Item();
            Bid aBid = new Bid();
    
            anItem.getBids().add(aBid);
            aBid.setItem(anItem);
    
            assertEquals(anItem.getBids().size(), 1);
            assertTrue(anItem.getBids().contains(aBid));
            assertEquals(aBid.getItem(), anItem);
    
            // 再次用方便的方法
            Bid secondBid = new Bid();
            anItem.addBid(secondBid);
    
            assertEquals(2, anItem.getBids().size());
            assertTrue(anItem.getBids().contains(secondBid));
            assertEquals(anItem, secondBid.getItem());
        }
    
        @Test
        public void validateItem() {
            ValidatorFactory factory = Validation.buildDefaultValidatorFactory();
            Validator validator = factory.getValidator();
    
            Item item = new Item();
            item.setName("Some Item");
            item.setAuctionEnd(new Date());
    
            Set<ConstraintViolation<Item>> violations = validator.validate(item);
    
            // 我们有一个验证错误，拍卖结束日期不在将来！
            assertEquals(1, violations.size());
    
            ConstraintViolation<Item> violation = violations.iterator().next();
            String failedPropertyName =
                    violation.getPropertyPath().iterator().next().getName();
    
            assertEquals(failedPropertyName, "auctionEnd");
    
            if (Locale.getDefault().getLanguage().equals("en"))
                assertEquals(violation.getMessage(), "must be in the future");
        }
    
    }

/examples/src/test/java/org/jpwh/test/simple/SimpleTransitions.java

package org.jpwh.test.simple;
    
    import org.hibernate.Session;
    import org.hibernate.jdbc.Work;
    import org.jpwh.env.JPATest;
    import org.jpwh.model.simple.Address;
    import org.jpwh.model.simple.Item;
    import org.jpwh.model.simple.User;
    import org.testng.annotations.Test;
    
    import javax.persistence.EntityManager;
    import javax.persistence.EntityManagerFactory;
    import javax.persistence.FlushModeType;
    import javax.persistence.PersistenceUnitUtil;
    import javax.transaction.Status;
    import javax.transaction.UserTransaction;
    import java.sql.Connection;
    import java.sql.PreparedStatement;
    import java.sql.SQLException;
    import java.util.HashSet;
    import java.util.Set;
    import java.util.concurrent.Callable;
    import java.util.concurrent.Executors;
    
    import static org.testng.Assert.*;
    import static org.testng.Assert.assertEquals;
    
    //简单的过渡
    public class SimpleTransitions extends JPATest {
    
        @Override
        public void configurePersistenceUnit() throws Exception {
            configurePersistenceUnit("SimplePU");
        }
    
        @Test
        public void basicUOW() {
            EntityManager em = null;
            UserTransaction tx = TM.getUserTransaction();
            try {
                tx.begin();
                em = JPA.createEntityManager(); // 应用程序管理
    
                Item someItem = new Item();
                someItem.setName("Some Item");
                em.persist(someItem);
    
                tx.commit(); // 同步/刷新持久性上下文
            } catch (Exception ex) {
                // 事务回滚，异常处理
                try {
                    if (tx.getStatus() == Status.STATUS_ACTIVE
                        || tx.getStatus() == Status.STATUS_MARKED_ROLLBACK)
                        tx.rollback();
                } catch (Exception rbEx) {
                    System.err.println("Rollback of transaction failed, trace follows!");
                    rbEx.printStackTrace(System.err);
                }
                throw new RuntimeException(ex);
            } finally {
                if (em != null && em.isOpen())
                    em.close(); // 你创建它，你关闭它！
            }
        }
    
        @Test
        public void makePersistent() throws Exception {
            UserTransaction tx = TM.getUserTransaction();
            try {
                EntityManager em;
    
                tx.begin();
                em = JPA.createEntityManager();
                Item item = new Item();
                item.setName("Some Item"); // Item#name is NOT NULL!
    
                em.persist(item);
    
                Long ITEM_ID = item.getId(); // Has been assigned
    
                tx.commit();
                em.close();
    
                tx.begin();
                em = JPA.createEntityManager();
                assertEquals(em.find(Item.class, ITEM_ID).getName(), "Some Item");
                tx.commit();
                em.close();
    
            } finally {
                TM.rollback();
            }
        }
    
        @Test
        public void retrievePersistent() throws Exception {
            UserTransaction tx = TM.getUserTransaction();
            try {
                tx.begin();
                EntityManager em = JPA.createEntityManager();
                Item someItem = new Item();
                someItem.setName("Some Item");
                em.persist(someItem);
                tx.commit();
                em.close();
                long ITEM_ID = someItem.getId();
    
                {
                    tx.begin();
                    em = JPA.createEntityManager();
    
                    // Hit the database if not already in persistence context
                    Item item = em.find(Item.class, ITEM_ID);
    
                    if (item != null)
                        item.setName("New Name"); // Modify
    
                    tx.commit(); // Flush: Dirty check and SQL UPDATE
                    em.close();
                }
    
                {
                    tx.begin();
                    em = JPA.createEntityManager();
    
                    Item itemA = em.find(Item.class, ITEM_ID);
                    Item itemB = em.find(Item.class, ITEM_ID); // Repeatable read
    
                    assertTrue(itemA == itemB);
                    assertTrue(itemA.equals(itemB));
                    assertTrue(itemA.getId().equals(itemB.getId()));
    
                    tx.commit(); // Flush: Dirty check and SQL UPDATE
                    em.close();
                }
    
                tx.begin();
                em = JPA.createEntityManager();
                assertEquals(em.find(Item.class, ITEM_ID).getName(), "New Name");
                tx.commit();
                em.close();
            } finally {
                TM.rollback();
            }
        }
    
        @Test(expectedExceptions = org.hibernate.LazyInitializationException.class)
        public void retrievePersistentReference() throws Exception {
            UserTransaction tx = TM.getUserTransaction();
            try {
                tx.begin();
                EntityManager em = JPA.createEntityManager();
                Item someItem = new Item();
                someItem.setName("Some Item");
                em.persist(someItem);
                tx.commit();
                em.close();
                long ITEM_ID = someItem.getId();
    
                tx.begin();
                em = JPA.createEntityManager();
    
                /* 
    				如果持久性上下文已经包含具有给定标识符的<code> Item </code>
                    <code> Item </code>实例由<code> getReference()</code>返回，而不会触发数据库。
                    此外，如果目前正在管理具有该标识符的持久化实例<em>no</em>，那么一个空
                    占位符将由Hibernate代理生成。 这意味着<code> getReference()</code>不会
                    访问数据库，它不返回<code> null </code>，与<code> find()</code>不同。
                 */
                Item item = em.getReference(Item.class, ITEM_ID);
    
                /* 
    				JPA提供<code> PersistenceUnitUtil </code>辅助方法，例如<code> isLoaded()</code>
                    检测您是否使用未初始化的代理。
                */
                PersistenceUnitUtil persistenceUtil =
                    JPA.getEntityManagerFactory().getPersistenceUnitUtil();
                assertFalse(persistenceUtil.isLoaded(item));
    
                /* 
    				一旦您在代理上调用任何方法，例如<code> Item＃getName()</code>，
                    执行<code> SELECT </code>以完全初始化占位符。 这个规则的例外是
                    一种映射的数据库标识符getter方法，如<code> getId()</code>。 代理人
                    可能看起来像真实的东西，但它只是一个携带标识符值的占位符
                    它代表的实体实例。 如果代理服务器上不存在数据库记录
                    被初始化，将抛出一个<code> EntityNotFoundException </code>。
                 */
                // assertEquals(item.getName(), "Some Item");
                /* 
                   Hibernate有一个方便的静态<code> initialize()</code>方法，加载代理的数据。
                 */
                // Hibernate.initialize(item);
    
                tx.commit();
                em.close();
    
                /* 
    			在持久化上下文关闭之后，<code>item</code>处于分离状态。
    			如果你这样做在持久化上下文仍然打开时，不初始化代理，如果你访问代理,您将得到一个
    			<code> LazyInitializationException </code>。
    			你不能加载，一旦持久化上下文关闭，就按需数据。
    			解决方案很简单:加载
    			关闭持久化上下文之前的数据。
                 */
                assertEquals(item.getName(), "Some Item");
            } finally {
                TM.rollback();
            }
        }
    
        @Test
        public void makeTransient() throws Exception {
            UserTransaction tx = TM.getUserTransaction();
            try {
                tx.begin();
                EntityManager em = JPA.createEntityManager();
                Item someItem = new Item();
                someItem.setName("Some Item");
                em.persist(someItem);
                tx.commit();
                em.close();
                long ITEM_ID = someItem.getId();
    
                tx.begin();
                em = JPA.createEntityManager();
                /* 
    				如果调用<code>find()</code>，Hibernate将执行<code>SELECT</code>
                    加载<code>Item</code>。 如果你调用<code> getReference()</code>，Hibernate
                    将尝试避免<code>SELECT</code>并返回代理。
                 */
                Item item = em.find(Item.class, ITEM_ID);
                //Item item = em.getReference(Item.class, ITEM_ID);
    
                /* 
    			       调用<code>remove()</code>将队列化实体删除
                    工作单位完成，现在已被删除<em>removed</em>。如果<code>remove()</code>
                    在代理上调用，Hibernate将执行<code>SELECT</code>来加载数据。
                    实体实例必须在生命周期过渡期间完全初始化。 你可能
    				是否启用了生命周期回调方法或实体侦听器
                    （请参阅<a href="#EventListenersInterceptors"/>），实例必须通过这些
                    拦截器完成其整个生命周期。
                 */
                em.remove(item);
    
                /* 
    				 被删除状态的实体不再处于持久状态，这可以是
                     使用<code> contains()</code>操作进行检查。
                 */
                assertFalse(em.contains(item));
    
                /* 
                   	您可以使删除的实例再次持久化，取消删除。
                 */
                // em.persist(item);
    
                // hibernate.use_identifier_rollback已启用，它现在看起来像一个暂时的实例
                assertNull(item.getId());
    
                /* 
    				当事务提交时，Hibernate会同步状态转换
                    数据库并执行SQL <code> DELETE </code>。 JVM垃圾收集器检测到
                    <code> item </code>不再被任何人引用，最后删除最后一个跟踪
                    数据。
                 */
                tx.commit();
                em.close();
    
                tx.begin();
                em = JPA.createEntityManager();
                item = em.find(Item.class, ITEM_ID);
                assertNull(item);
                tx.commit();
                em.close();
            } finally {
                TM.rollback();
            }
        }
    
        @Test
        public void refresh() throws Exception {
            UserTransaction tx = TM.getUserTransaction();
            try {
                tx.begin();
                EntityManager em = JPA.createEntityManager();
                Item someItem = new Item();
                someItem.setName("Some Item");
                em.persist(someItem);
                tx.commit();
                em.close();
                final long ITEM_ID = someItem.getId();
    
                tx.begin();
                em = JPA.createEntityManager();
    
                Item item = em.find(Item.class, ITEM_ID);
                item.setName("Some Name");
    
                // 有人更新数据库中的这一行！
                Executors.newSingleThreadExecutor().submit(new Callable<Object>() {
                    @Override
                    public Object call() throws Exception {
                        UserTransaction tx = TM.getUserTransaction();
                        try {
                            tx.begin();
                            EntityManager em = JPA.createEntityManager();
    
                            Session session = em.unwrap(Session.class);
                            session.doWork(new Work() {
                                @Override
                                public void execute(Connection con) throws SQLException {
                                    PreparedStatement ps = con.prepareStatement("update ITEM set name = ? where ID = ?");
                                    ps.setString(1, "Concurrent Update Name");
                                    ps.setLong(2, ITEM_ID);
    
                                    /* 替代方法：在刷新时收到EntityNotFoundException
                                    PreparedStatement ps = con.prepareStatement("delete from ITEM where ID = ?");
                                    ps.setLong(1, ITEM_ID);
                                    */
    
                                    if (ps.executeUpdate() != 1)
                                        throw new SQLException("ITEM row was not updated");
                                }
                            });
    
                            tx.commit();
                            em.close();
    
                        } catch (Exception ex) {
                            TM.rollback();
                            throw new RuntimeException("Concurrent operation failure: " + ex, ex);
                        }
                        return null;
                    }
                }).get();
    
                String oldName = item.getName();
                em.refresh(item);
                assertNotEquals(item.getName(), oldName);
                assertEquals(item.getName(), "Concurrent Update Name");
    
                tx.commit(); // 刷新：脏检查和SQL UPDATE
                em.close();
    
            } finally {
                TM.rollback();
            }
        }
    
        @Test(groups = {"H2", "POSTGRESQL", "ORACLE"})
        public void replicate() throws Exception {
    
            Long ITEM_ID;
            try {
                UserTransaction tx = TM.getUserTransaction();
                tx.begin();
                EntityManager em = JPA.createEntityManager();
                Item someItem = new Item();
                someItem.setName("Some Item");
                em.persist(someItem);
                tx.commit();
                em.close();
                ITEM_ID = someItem.getId();
            } finally {
                TM.rollback();
            }
    
            UserTransaction tx = TM.getUserTransaction();
            try {
                tx.begin();
    
                EntityManager emA = getDatabaseA().createEntityManager();
                Item item = emA.find(Item.class, ITEM_ID);
    
                EntityManager emB = getDatabaseB().createEntityManager();
                emB.unwrap(Session.class)
                    .replicate(item, org.hibernate.ReplicationMode.LATEST_VERSION);
    
                tx.commit();
                emA.close();
                emB.close();
            } finally {
                TM.rollback();
            }
        }
    
        protected EntityManagerFactory getDatabaseA() {
            return JPA.getEntityManagerFactory();
        }
    
        protected EntityManagerFactory getDatabaseB() {
    		 // TODO：失败，因为我们不能在同一事务中招募两个非XA连接
        	 //在MySQL上 XA在MySQL中破坏，所以我们必须使用Bitronix XA包装器，它可以
             //每个事务只处理一个非XA资源。 请参阅DatabaseProduct.java
            return JPA.getEntityManagerFactory();
        }
    
        @Test
        public void flushModeType() throws Exception {
            UserTransaction tx = TM.getUserTransaction();
            Long ITEM_ID;
            try {
                tx.begin();
                EntityManager em = JPA.createEntityManager();
                Item someItem = new Item();
                someItem.setName("Original Name");
                em.persist(someItem);
                tx.commit();
                em.close();
                ITEM_ID = someItem.getId();
            } finally {
                TM.rollback();
            }
    
            try {
                tx.begin();
                EntityManager em = JPA.createEntityManager();
    
                Item item = em.find(Item.class, ITEM_ID);
                item.setName("New Name");
    
                // 禁用刷新之前查询:
                em.setFlushMode(FlushModeType.COMMIT);
    
                assertEquals(
                    em.createQuery("select i.name from Item i where i.id = :id")
                        .setParameter("id", ITEM_ID).getSingleResult(),
                    "Original Name"
                );
    
                tx.commit(); // Flush!
                em.close();
            } finally {
                TM.rollback();
            }
        }
    
        @Test
        public void scopeOfIdentity() throws Exception {
            UserTransaction tx = TM.getUserTransaction();
            try {
                tx.begin();
                EntityManager em = JPA.createEntityManager();
                Item someItem = new Item();
                someItem.setName("Some Item");
                em.persist(someItem);
                tx.commit();
                em.close();
                long ITEM_ID = someItem.getId();
    
                tx.begin();
                em = JPA.createEntityManager();
    
                Item a = em.find(Item.class, ITEM_ID);
                Item b = em.find(Item.class, ITEM_ID);
                assertTrue(a == b);
                assertTrue(a.equals(b));
                assertEquals(a.getId(), b.getId());
    
                tx.commit();
                em.close();
                // PC is gone, 'a' and 'b' are now references to instances in detached state!
    
                tx.begin();
                em = JPA.createEntityManager();
    
                Item c = em.find(Item.class, ITEM_ID);
                assertTrue(a != c); // The 'a' reference is still detached!
                assertFalse(a.equals(c));
                assertEquals(a.getId(), c.getId());
    
                tx.commit();
                em.close();
    
                Set<Item> allItems = new HashSet<>();
                allItems.add(a);
                allItems.add(b);
                allItems.add(c);
                assertEquals(allItems.size(), 2); // 这似乎是错的和任意的！
    
            } finally {
                TM.rollback();
            }
        }
    
        @Test
        public void detach() throws Exception {
            UserTransaction tx = TM.getUserTransaction();
            try {
                tx.begin();
                EntityManager em = JPA.createEntityManager();
    
                User someUser = new User();
                someUser.setUsername("johndoe");
                someUser.setHomeAddress(new Address("Some Street", "1234", "Some City"));
                em.persist(someUser);
                tx.commit();
                em.close();
                long USER_ID = someUser.getId();
    
                tx.begin();
                em = JPA.createEntityManager();
    
                User user = em.find(User.class, USER_ID);
    
                em.detach(user);
    
                assertFalse(em.contains(user));
    
                tx.commit();
                em.close();
            } finally {
                TM.rollback();
            }
        }
    
        @Test
        public void mergeDetached() throws Exception {
            UserTransaction tx = TM.getUserTransaction();
            try {
                tx.begin();
                EntityManager em = JPA.createEntityManager();
    
                User detachedUser = new User();
                detachedUser.setUsername("foo");
                detachedUser.setHomeAddress(new Address("Some Street", "1234", "Some City"));
                em.persist(detachedUser);
                tx.commit();
                em.close();
                long USER_ID = detachedUser.getId();
    
                detachedUser.setUsername("johndoe");
    
                tx.begin();
                em = JPA.createEntityManager();
    
                User mergedUser = em.merge(detachedUser);
                // 合并后丢弃'detachUser'引用！
    
                // 'mergedUser'处于持久状态
                mergedUser.setUsername("doejohn");
    
                tx.commit(); // UPDATE在数据库中
                em.close();
    
                tx.begin();
                em = JPA.createEntityManager();
                User user = em.find(User.class, USER_ID);
                assertEquals(user.getUsername(), "doejohn");
                tx.commit();
                em.close();
            } finally {
                TM.rollback();
            }
        }
    
    }

[20170703220612026]: /images/20220613/4ff1438b9239463e993146be0acc3836.png
[20170703222034505]: /images/20220613/210bccff71ff4540acdde80638285f1d.png
[20170703222508104]: /images/20220613/cad913acce7f4c4ea83cefb6fa945618.png