关于方法的Spring @Transactional注释的一些说明

时间：2013-03-08 18:07:50

标签： java spring hibernate spring-mvc annotations

我是Spring世界的新手，我开发了一个使用Spring 3.2.1和Hibernate 4.1.9来实现DAO的简单项目。该项目工作正常，但我对使用 @Transactional Spring注释对此DAO的CRUD方法有疑问。

这是实现项目的CRUD操作的类的完整代码：

package org.andrea.myexample.HibernateOnSpring.dao;

import java.util.List;

import org.andrea.myexample.HibernateOnSpring.entity.Person;

import org.hibernate.Criteria;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;
import org.hibernate.service.ServiceRegistryBuilder;
import org.springframework.transaction.annotation.Transactional;

public class PersonDAOImpl implements PersonDAO {

    // Factory per la creazione delle sessioni di Hibernate:
    private static SessionFactory sessionFactory;

    // Metodo Setter per l'iniezione della dipendenza della SessionFactory:
    public void setSessionFactory(SessionFactory sessionFactory) {
        this.sessionFactory = sessionFactory;
    }

    /** CREATE CRUD Operation:
     * Aggiunge un nuovo record rappresentato nella tabella rappresentato
     * da un oggetto Person
     */
    @Transactional(readOnly = false)
    public Integer addPerson(Person p) {

        System.out.println("Inside addPerson()");

        Session session = sessionFactory.openSession();

        Transaction tx = null;
        Integer personID = null;

        try {
            tx = session.beginTransaction();

            personID = (Integer) session.save(p);
            tx.commit();
        } catch (HibernateException e) {
            if (tx != null)
                tx.rollback();
            e.printStackTrace();
        } finally {
            session.close();
        }

        return personID;

    }

    // READ CRUD Operation (legge un singolo record avente uno specifico id):
    public Person getById(int id) {

        System.out.println("Inside getById()");

        Session session = sessionFactory.openSession();

        Transaction tx = null;          
        Person retrievedPerson = null;  

        try {
            tx = session.beginTransaction();
            retrievedPerson = (Person) session.get(Person.class, id);
            tx.commit();
        }catch (HibernateException e) { 
            if (tx != null)                 
                tx.rollback();          
            e.printStackTrace();
        } finally {                 
            session.close();
        }

        return retrievedPerson;
    }

    // READ CRUD Operation (recupera la lista di tutti i record nella tabella):
    @SuppressWarnings("unchecked")
    public List<Person> getPersonsList() {

        System.out.println("Inside getPersonsList()");

        Session session = sessionFactory.openSession();
        Transaction tx = null;
        List<Person> personList = null;

        try {
            tx = session.beginTransaction();
            Criteria criteria = session.createCriteria(Person.class);
            personList = criteria.list();
            System.out.println("personList: " + personList);
            tx.commit();
        }catch (HibernateException e) { 
            if (tx != null)                 
                tx.rollback();          
            e.printStackTrace();
        } finally {
            session.close();
        }
        return personList;
    }

    // DELETE CRUD Operation (elimina un singolo record avente uno specifico id):
    public void delete(int id) {

        System.out.println("Inside delete()");

        Session session = sessionFactory.openSession();
        Transaction tx = null;

        try {
            tx = session.beginTransaction();
            Person personToDelete = getById(id);
            session.delete(personToDelete);
            tx.commit();
        }catch (HibernateException e) { 
            if (tx != null)                 
                tx.rollback();          
            e.printStackTrace();
        } finally {
            session.close();
        }

    }

    @Transactional
    public void update(Person personToUpdate) {

        System.out.println("Inside update()");

        Session session = sessionFactory.openSession();
        Transaction tx = null;

        try {
            System.out.println("Insite update() method try");
            tx = session.beginTransaction();
            session.update(personToUpdate);

            tx.commit();
        }catch (HibernateException e) { 
            if (tx != null)                 
                tx.rollback();          
            e.printStackTrace();
        } finally {
            session.close();
        }   

    }

}

好的，你可以看到一些方法是使用@Transactional注释注释的。

我在这里阅读官方文档http://static.springsource.org/spring/docs/3.2.x/spring-framework-reference/html/transaction.html，关于在方法上使用此注释，它看到：使用@Transactional注释的方法必须具有事务语义，但它意味着什么事务语义？

这意味着必须将执行方法视为执行事务？因此，这意味着必须将方法操作视为可能导致成功或失败的单个操作，如果成功，操作结果必须是永久性的，而如果未能返回到之前的状态，则交易的开始。

这是在方法上使用 @Transactional 注释的含义吗？

addPerson（）方法的@Transactional注释中 readOnly = false 属性的确切含义是什么？这意味着我还可以在数据库中写一条记录（而不仅仅是读取它）还是什么？怀疑是相关的，因为我已经明白，默认情况下，使用@Transactional注释定义的交易是读/写而不只是阅读...... 我还尝试删除（readOnly = false）属性并且仍能正常工作（在数据库表中插入新记录）

下面的dout是：“为什么某些方法使用@Transactional注释和其他一些方法没有注释？用@Transactional来表示所有CRUD方法是一个很好的实践吗？”

TNX

安德烈

2 个答案:

答案 0 :(得分：69)

首先，你不应该使DAO方法成为事务性的，而是服务方法。

其次，使用Transactional是一种让Spring为您启动和提交/回滚事务的方法。所以你不应该自己启动和提交交易。

第三：只有当你使用知道如何将Hibernate会话与事务关联的事务管理器（通常是HibernateTransactionManager）时，这才有效。会话工厂也应该由Spring处理，并由Spring在你的DAO中注入。 DAO的代码应如下所示：

第四：你不应该打开一个新的会话，而是获得当前的会话，与春天的当前交易相关联。

public class PersonDAOImpl implements PersonDAO {

    @Autowired
    private SessionFactory sessionFactory;

    public Integer addPerson(Person p) {
        Session session = sessionFactory.getCurrentSession();
        Integer personID = (Integer) session.save(p);
        return personID;
    }

    public Person getById(int id) {
        Session session = sessionFactory.getCurrentSession();
        Person retrievedPerson = (Person) session.get(Person.class, id);
        return retrievedPerson;
    }

    @SuppressWarnings("unchecked")
    public List<Person> getPersonsList() {
        Session session = sessionFactory.getCurrentSession();
        Criteria criteria = session.createCriteria(Person.class);
        return criteria.list();
    }

    public void delete(int id) {
        Session session = sessionFactory.getCurrentSession();
        Person personToDelete = getById(id);
        session.delete(personToDelete);
    }

    public void update(Person personToUpdate) {
        Session session = sessionFactory.getCurrentSession();
        session.update(personToUpdate);
    }
}

阅读the documentation了解详情。

答案 1 :(得分：3)

@Transactional用于该方法。

我们首先在方法级别声明它打开事务，执行操作并关闭事务。

如果操作失败，则会回滚，如果操作成功，则会自动提交

最后约为@Transactional注释＆amp; short。

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans" 
    xmlns:p="http://www.springframework.org/schema/p"
    xmlns:context="http://www.springframework.org/schema/context" 
    xmlns:tx="http://www.springframework.org/schema/tx" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context-3.0.xsd
        http://www.springframework.org/schema/tx
        http://www.springframework.org/schema/tx/spring-tx.xsd
        ">

    <!-- Scans the classpath for annotated components that will be auto-registered as Spring beans -->
    <context:component-scan base-package="hu.daniel.hari.learn.spring" />
    <!-- Activates various annotations to be detected in bean classes e.g: @Autowired -->
    <context:annotation-config />


    <!-- creating the internal datasource object -->

    <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
        <property name="driverClassName" value="org.hsqldb.jdbcDriver" />
        <property name="url" value="jdbc:hsqldb:mem://productDb" />
        <property name="username" value="sa" />
        <property name="password" value="" />
    </bean>

    <bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean"
            p:packagesToScan="hu.daniel.hari.learn.spring.orm.model"
            p:dataSource-ref="dataSource"
            >
        <property name="jpaVendorAdapter">
            <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
                <property name="generateDdl" value="true" />
                <property name="showSql" value="true" />

            </bean>
        </property>
    </bean>

    <!-- Transactions -->
    <bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
        <property name="entityManagerFactory" ref="entityManagerFactory" />
    </bean>
    <tx:annotation-driven transaction-manager="transactionManager" />

</beans>

package hu.daniel.hari.learn.spring.orm.main;

import hu.daniel.hari.learn.spring.orm.model.Product;
import hu.daniel.hari.learn.spring.orm.service.ProductService;

import java.util.Arrays;

import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.dao.DataAccessException;

public class SpringOrmMain {

    public static void main(String[] args) {

        //Create Spring application context
        ClassPathXmlApplicationContext ctx = new ClassPathXmlApplicationContext("classpath:/spring.xml");

        //Get service from context. (service's dependency (ProductDAO) is autowired in ProductService)
        ProductService productService = ctx.getBean(ProductService.class);

        //Do some data operation

        productService.add(new Product(1, "Bulb"));
        productService.add(new Product(2, "Dijone mustard"));

        System.out.println("listAll: " + productService.listAll());

        //Test transaction rollback (duplicated key)

        try {
            productService.addAll(Arrays.asList(new Product(3, "Book"), new Product(4, "Soap"), new Product(1, "Computer")));
        } catch (DataAccessException dataAccessException) {
        }

        //Test element list after rollback
        System.out.println("listAll: " + productService.listAll());

        ctx.close();
    }
}
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