两个操作要么同时成功，要么同时失败；

事务的一致性；

以前学ssh ssm都有事务管理service层通过applicationContext.xml配置，所有service方法都加上事务操作；

用来保证一致性，即service方法里的多个dao操作，要么同时成功，要么同时失败；

 

下面模拟用户转账，a用户转账给b用户200元；需要事务管理；

项目结构：

 

1.代码：　　　　　　　　　　　　　　　　　　　　

com.cy.entity.Account.java;

package com.cy.entity;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.Table;/** * 账户实体 * @author CY * */@Entity@Table(name="t_account")public class Account {        @Id    @GeneratedValue    private Integer id;        @Column(length=50)    private String userName;        private float balance;    //余额    public Integer getId() {        return id;    }    public void setId(Integer id) {        this.id = id;    }    public String getUserName() {        return userName;    }    public void setUserName(String userName) {        this.userName = userName;    }    public float getBalance() {        return balance;    }    public void setBalance(float balance) {        this.balance = balance;    }            }

账户dao接口：com.cy.dao.AccountDao.java:

package com.cy.dao;import org.springframework.data.jpa.repository.JpaRepository;import com.cy.entity.Account;/** * 账户Dao接口 * JpaRepository
      
       第二个参数是主键类型 * @author CY * */public interface AccountDao extends JpaRepository
       
        {}
       
      

账户service接口：com.cy.service.AccountService.java:

package com.cy.service;/** * 账户Service接口 * @author CY * */public interface AccountService {        /**     * 从fromUser转账到toUser，account钱；     * @param fromUser     * @param toUser     * @param account     */    public void transferAccounts(int fromUser, int toUser, float account);}

账户接口实现类：com.cy.service.impl.AccountServiceImpl.java;

package com.cy.service.impl;import javax.annotation.Resource;import javax.transaction.Transactional;import org.springframework.stereotype.Service;import com.cy.dao.AccountDao;import com.cy.entity.Account;import com.cy.service.AccountService;/** * 账户service实现类 * @author CY * */@Service("accountService")public class AccountServiceImpl implements AccountService{        @Resource    private AccountDao accountDao;        /**     * 从A用户转账到B用户account元；     * 也就是两个操作：     * A用户减去accout元，B用户加上account元     */    @Override    @Transactional    public void transferAccounts(int fromUser, int toUser, float account) {        Account a = accountDao.getOne(fromUser);        a.setBalance(a.getBalance() - account);        accountDao.save(a);                Account b = accountDao.getOne(toUser);        b.setBalance(b.getBalance() + account);        int i = 1/0;        //这里制造个异常        accountDao.save(b);    }    }

com.cy.controller.AccountController.java来模拟用户转账：

这里返回json数据格式，成功ok，失败no

package com.cy.controller;import javax.annotation.Resource;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.RestController;import com.cy.service.AccountService;/** * 账户Controller层 * @author CY * */@RestController@RequestMapping("/account")public class AccountController {        @Resource    private AccountService accountService;        @RequestMapping("/transfer")    public String transferAccount(){        try{            accountService.transferAccounts(1, 2, 200);            return "ok";        }catch(Exception e){            return "no";        }    }}

 

2.测试：

启动项目，查看新建的表t_account：

mysql> desc t_account;+-----------+-------------+------+-----+---------+----------------+| Field     | Type        | Null | Key | Default | Extra          |+-----------+-------------+------+-----+---------+----------------+| id        | int(11)     | NO   | PRI | NULL    | auto_increment || balance   | float       | NO   |     | NULL    |                || user_name | varchar(50) | YES  |     | NULL    |                |+-----------+-------------+------+-----+---------+----------------+

弄点数据：

mysql> select * from t_account;+----+---------+-----------+| id | balance | user_name |+----+---------+-----------+|  1 |     700 | zhangsan  ||  2 |     300 | lisi      |+----+---------+-----------+

浏览器http://localhost/account/transfer:

1）显示no，说明转账失败；

2）数据库数据，zhangsan仍然是700，lisi仍然是300，保证了数据一致性；

查看发出的sql：

Hibernate: select account0_.id as id1_0_0_, account0_.balance as balance2_0_0_, account0_.user_name as user_nam3_0_0_ from t_account account0_ where account0_.id=?Hibernate: select account0_.id as id1_0_0_, account0_.balance as balance2_0_0_, account0_.user_name as user_nam3_0_0_ from t_account account0_ where account0_.id=?

没有执行保存，全部弄完了才保存；

 

说明：

这里使用的是：import javax.transaction.Transactional;（这个是jpa规范）

使用import org.springframework.transaction.annotation.Transactional也行；（这个spring实现了jpa规范）