Beginning Spring学习笔记——第5章（二）Spring的JPA支持

Spring的JPA支持的好处

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• 更容易且更强大的持久化单元配置，不必使用META-INF/persistence.xml
• 更容易测试
• 自动EntityManager管理，且可注入DAO Bean中
• 常见的数据访问异常，异常层次结构变为Spring的
• 集成事务管理

在Spring容器中配置JPA

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Spring在同一个项目中提供三种不同方法配置EntityManagerFactory。

• LocalEntityManagerFactoryBean
  最基础且功能最有限的方法，从META-INF/persistence.xml中读取JPA配置，不允许使用Spring管理的DataSource实例且不支持分布式事务管理
• 通过JNDI进行EntityManagerFactory查找
  此时的Spring EntityManagerFactory Bean只不过是一个从JNDI获取的持久化单元委托
• LocalContainerEntityFactoryBean，最强大和灵活的JPA配置方法，对EntityManagerFactory完全控制

使用LocalContainerEntityManagerFactoryBean配置和使用JPA

接上一节的Book和Student类创建配置类

@Configurationpublic class Ch5Configuration {    @Bean    public DataSource dataSource() {        DriverManagerDataSource dataSource = new DriverManagerDataSource();        dataSource.setDriverClassName("org.h2.Driver");        dataSource.setUrl("jdbc:h2:tcp://localhost/~/test");        dataSource.setUsername("sa");        dataSource.setPassword("");        return dataSource;    }    private Map<String,?> jpaProperties() {        Map<String,String> jpaPropertiesMap = new HashMap<String,String>();        jpaPropertiesMap.put("hibernate.dialect", "org.hibernate.dialect.H2Dialect");        jpaPropertiesMap.put("hibernate.hbm2ddl.auto", "update");        return jpaPropertiesMap;    }    @Bean    public LocalContainerEntityManagerFactoryBean entityManagerFactory() {        LocalContainerEntityManagerFactoryBean factoryBean =             new LocalContainerEntityManagerFactoryBean();        factoryBean.setPersistenceProviderClass(HibernatePersistenceProvider.class);        factoryBean.setDataSource(dataSource());        factoryBean.setPackagesToScan("com.wiley.beginningspring.ch5");        factoryBean.setJpaPropertyMap(jpaProperties());        return factoryBean;    }}

为使用Spring管理的DataSource和EntityManagerFactory，主函数中也要创建Spring容器

public class Main {    public static void main(String[] args) {        ApplicationContext applicationContext = new AnnotationConfigApplicationContext(                Ch5Configuration.class);        EntityManagerFactory entityManagerFactory = applicationContext                .getBean(EntityManagerFactory.class);        EntityManager entityManager = entityManagerFactory                .createEntityManager();        EntityTransaction transaction = entityManager.getTransaction();        transaction.begin();        Student student = new Student();        student.setFirstName("Madoka");        student.setLastName("Kaname");        entityManager.persist(student);        transaction.commit();        entityManager.close();    }}

完成插入操作后查看数据库：

学生成功被插入。

基于纯JPA实现DAO

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可以在字段或方法级别使用@PersistenceContext和@PersistenceUnit注解，前者表示对EntityManagerFactory的依赖，后者表示对EntityManager的依赖

使用@PersistenceUnit获取EntityManagerFactory

此时需要在Dao实现类中加入EntityManagerFactory字段并在其上放置@PersistenceUnit注解将entityManagerFactory注入到DAO类中。

public class StudentDaoJpaImpl {    @PersistenceUnit    private EntityManagerFactory entityManagerFactory;    public void save(Student student) {        EntityManager entityManager = entityManagerFactory                .createEntityManager();        EntityTransaction transaction = entityManager.getTransaction();        transaction.begin();        entityManager.persist(student);        transaction.commit();        entityManager.close();    }}

此时还要在配置文件中加入DAO类的Bean：

    @Bean    public StudentDaoJpaImpl studentDao() {        StudentDaoJpaImpl dao = new StudentDaoJpaImpl();        return dao;    }

然后在主函数里用该DAO类插入一个Student实例：

public class Main {    public static void main(String[] args) {        ApplicationContext applicationContext = new AnnotationConfigApplicationContext(                Ch5Configuration.class);        StudentDaoJpaImpl dao = applicationContext.getBean(StudentDaoJpaImpl.class);        Student student = new Student();        student.setFirstName("Sayaka");        student.setLastName("Miki");        dao.save(student);    }}

运行程序发现插入成功

使用@PersistenceContext获取EntityManager

此时要用@EnableTransactionManagement注解标识配置类启用Spring容器管理事务，新配置类为：

@Configuration@EnableTransactionManagementpublic class Ch5Configuration {    @Bean    public DataSource dataSource() {        DriverManagerDataSource dataSource = new DriverManagerDataSource();        dataSource.setDriverClassName("org.h2.Driver");        dataSource.setUrl("jdbc:h2:tcp://localhost/~/test");        dataSource.setUsername("sa");        dataSource.setPassword("");        return dataSource;    }    private Map<String,?> jpaProperties() {        Map<String,String> jpaPropertiesMap = new HashMap<String,String>();        jpaPropertiesMap.put("hibernate.dialect", "org.hibernate.dialect.H2Dialect");        jpaPropertiesMap.put("hibernate.hbm2ddl.auto", "update");        return jpaPropertiesMap;    }    @Bean    public LocalContainerEntityManagerFactoryBean entityManagerFactory() {        LocalContainerEntityManagerFactoryBean factoryBean =             new LocalContainerEntityManagerFactoryBean();        factoryBean.setPersistenceProviderClass(HibernatePersistenceProvider.class);        factoryBean.setDataSource(dataSource());        factoryBean.setPackagesToScan("com.wiley.beginningspring.ch5");        factoryBean.setJpaPropertyMap(jpaProperties());        return factoryBean;    }    @Bean    public StudentDaoJpaImpl studentDao() {        StudentDaoJpaImpl dao = new StudentDaoJpaImpl();        return dao;    }    @Bean    @Autowired    public PlatformTransactionManager transactionManager(        EntityManagerFactory entityManagerFactory) {        JpaTransactionManager transactionManager = new JpaTransactionManager();        transactionManager.setEntityManagerFactory(entityManagerFactory);        return transactionManager;    }    @Bean    public BookDao bookDao() {        BookDaoJpaImpl bean = new BookDaoJpaImpl();        return bean;    }    @Bean    public BookService bookService() {        BookServiceImpl bean = new BookServiceImpl();        bean.setBookDao(bookDao());        return bean;    }}

然后创建BookDao接口和它的实现类进行持久化操作。由于@PersistenceContext注解是与EntityManager绑定，因此被注入的是EntityManager实例。

public interface BookDao {    public void save(Book book);}public class BookDaoJpaImpl implements BookDao {    @PersistenceContext    private EntityManager entityManager;    @Override    public void save(Book book) {        entityManager.persist(book);    }}

再创建服务层的BookService接口和其实现类处理事务管理。

public interface BookService {    public void save(Book book);}@Transactionalpublic class BookServiceImpl implements BookService {    private BookDao bookDao;    public void setBookDao(BookDao bookDao) {        this.bookDao = bookDao;    }    @Override    public void save(Book book) {        bookDao.save(book);    }}

以上二者的Bean都已经定义在了新配置文件中完成了向服务层注入dao层。
最后在主函数中执行对bookService的Bean查找，对新的Book实体进行持久化操作。

public class Main {    public static void main(String[] args) {        ApplicationContext applicationContext =             new AnnotationConfigApplicationContext(Ch5Configuration.class);        BookService bookService = applicationContext.getBean(BookService.class);        Book book = new Book();        book.setName("The Order of Things");        bookService.save(book);    }}

运行得到结果，成功插入书籍

处理和转换异常

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只需要用@Repository注解标注DAO实现类，

@Repositorypublic class BookDaoJpaImpl implements BookDao {    @PersistenceContext    private EntityManager entityManager;    @Override    public void save(Book book) {        entityManager.persist(book);    }}

然后在配置类中加入PersistenceExceptionTranslationPostProcessor的Bean，

    @Bean    public static PersistenceExceptionTranslationPostProcessor         persistenceExceptionTranslationPostProcessor() {        PersistenceExceptionTranslationPostProcessor bean =         new PersistenceExceptionTranslationPostProcessor();        return bean;    }

就可以在服务层通过一个try-catch语句捕捉转化为DataAccessException的异常了。

    @Override    public void save(Book book) {        try{            //Perform some business logic here            bookDao.save(book);        } catch (DataAccessException ex) {            //handle the data access exception without depending on particular data access technology used beneath    }

在Spring环境中进一步配置JPA

JpaDialect

通过该接口可以配置如下高级功能：

• 应用特定事务语义，比如自定义隔离级别或者事务超时
• 获取事务性JDBC连接，以便向基于JDBC的DAO公开
• 将PersistenceExcept转换到Spring DataAccessException的高级功能

默认实现为不提供任何上述功能的DefaultJpaDialect，使用上述功能需要指定特定方言类，比如HibernateJpaDialect。

JpaVendorAdapter

用于激活与供应商有关的高级功能，例如可以将LocalContainerEntityManagerFactoryBean中一下代码注释掉集中配置和管理：

    @Bean    public LocalContainerEntityManagerFactoryBean entityManagerFactory() {        LocalContainerEntityManagerFactoryBean factoryBean =             new LocalContainerEntityManagerFactoryBean();        factoryBean.setDataSource(dataSource());        //factoryBean.setJpaPropertyMap(jpaProperties());        //factoryBean.setPersistenceProviderClass(HibernatePersistenceProvider.class);        //factoryBean.setJpaDialect(new HibernateJpaDialect());        factoryBean.setJpaVendorAdapter(jpaVendorAdapter());        return factoryBean;    }    @Bean    public JpaVendorAdapter jpaVendorAdapter() {        HibernateJpaVendorAdapter jpaVendorAdapter = new HibernateJpaVendorAdapter();        jpaVendorAdapter.setGenerateDdl(true);        jpaVendorAdapter.setDatabase(Database.H2);        return jpaVendorAdapter;    }

JPA加载时编制

在配置类上添加@EnableLoadTimeWeaving启用加载时编织