spring之为什么要使用事务？（一）

问题描述：现在我们有一个数据库：spring

三张表：account、book、book_stock

account存储着用户以及账户余额。book存储着书号、名字和购买一本所需金额。book_stock存储着书号以及对应的库存。

现在我们有这么一个需求：用户买一本书，先让书的库存减一，然后在让用户余额减去相应的金额。我们来看如何处理。

新建一个Java project，在项目下新建一个lib文件夹，在文件夹中加入以下包：

选中这些包，点击鼠标右键，选择build path，选择add to build path。

然后建立以下的目录结构：

一、配置连接数据库

db.properties

jdbc.user=root
jdbc.password=123456
jdbc.driverClass=com.mysql.jdbc.Driver
jdbc.jdbcUrl=jdbc:mysql:///spring
jdbc.initPoolSize=5
jdbc.maxPoolSize=10

在applicationContex.xml中

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:context="http://www.springframework.org/schema/context"
    xmlns:tx="http://www.springframework.org/schema/tx"
    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-4.0.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.0.xsd">
    
    <!-- 导入资源文件 -->
    <context:property-placeholder location="classpath:db.properties"/>
    
    <!-- 配置 C3P0 数据源 -->
    <bean id="dataSource"
        class="com.mchange.v2.c3p0.ComboPooledDataSource">
        <property name="user" value="${jdbc.user}"></property>
        <property name="password" value="${jdbc.password}"></property>
        <property name="jdbcUrl" value="${jdbc.jdbcUrl}"></property>
        <property name="driverClass" value="${jdbc.driverClass}"></property>

        <property name="initialPoolSize" value="${jdbc.initPoolSize}"></property>
        <property name="maxPoolSize" value="${jdbc.maxPoolSize}"></property>
    </bean>
    
    
</beans>

二、利用基于注解的方式配置bean

向applicationContext.xml中加入

<context:component-scan base-package="com.gong.spring"></context:component-scan>

三、配置JdbcTemplate，并利用JdbcTemplate操作数据库

向applicationContext.xml中加入

    <!-- 配置 Spirng 的 JdbcTemplate -->
    <bean id="jdbcTemplate" 
        class="org.springframework.jdbc.core.JdbcTemplate">
        <property name="dataSource" ref="dataSource"></property>
    </bean>

BookShopDao.java

package com.gong.spring.tx;

public interface BookShopDao {
    
    //根据书号获取书的单价
    public int findBookPriceByIsbn(String isbn);
    //更新书的库存，使书号对应的库存-1
    public void updateBookStock(String isbn);
    //更新账户余额：使username的balance-price
    public void updateUserAccount(String username, int price);
}

BookShopDaoImpl.java

package com.gong.spring.tx;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.stereotype.Repository;

@Repository("bookShopDao")
public class BookShopDaoImpl implements BookShopDao {

    @Autowired
    private JdbcTemplate jdbcTemplate;
    
    @Override
    public int findBookPriceByIsbn(String isbn) {
        String sql = "SELECT price FROM book WHERE isbn = ?";
        return jdbcTemplate.queryForObject(sql, Integer.class, isbn);
    }

    @Override
    public void updateBookStock(String isbn) {
        String sql2 = "SELECT stock FROM book_stock WHERE isbn = ?";
        int stock = jdbcTemplate.queryForObject(sql2, Integer.class, isbn);
        //检查书的库存是否足够，如果不够，就抛出异常
        if(stock == 0){
            throw new BookStockException("库存不足!");
        }
        
        String sql = "UPDATE book_stock SET stock = stock -1 WHERE isbn = ?";
        jdbcTemplate.update(sql, isbn);
    }

    @Override
    public void updateUserAccount(String username, int price) {
        String sql2 = "SELECT balance FROM account WHERE username = ?";
        int balance = jdbcTemplate.queryForObject(sql2, Integer.class, username);
        if(balance < price){
            throw new UserAccountException("余额不足!");
        }
        
        String sql = "UPDATE account SET balance = balance - ? WHERE username = ?";
        jdbcTemplate.update(sql, price, username);
    }

}

需要注意的是，当存在余额不足或者库存不足时，需要抛出异常，我们需要自己定义该抛出的异常。

BookStockException.java

package com.gong.spring.tx;

public class BookStockException extends RuntimeException{

    /**
     * 
     */
    private static final long serialVersionUID = 1L;

    public BookStockException() {
        super();
        // TODO Auto-generated constructor stub
    }

    public BookStockException(String message, Throwable cause,
            boolean enableSuppression, boolean writableStackTrace) {
        super(message, cause, enableSuppression, writableStackTrace);
        // TODO Auto-generated constructor stub
    }

    public BookStockException(String message, Throwable cause) {
        super(message, cause);
        // TODO Auto-generated constructor stub
    }

    public BookStockException(String message) {
        super(message);
        // TODO Auto-generated constructor stub
    }

    public BookStockException(Throwable cause) {
        super(cause);
        // TODO Auto-generated constructor stub
    }

    
}

UserAccountException.java

package com.gong.spring.tx;

public class UserAccountException extends RuntimeException{

    /**
     * 
     */
    private static final long serialVersionUID = 1L;

    public UserAccountException() {
        super();
        // TODO Auto-generated constructor stub
    }

    public UserAccountException(String message, Throwable cause,
            boolean enableSuppression, boolean writableStackTrace) {
        super(message, cause, enableSuppression, writableStackTrace);
        // TODO Auto-generated constructor stub
    }

    public UserAccountException(String message, Throwable cause) {
        super(message, cause);
        // TODO Auto-generated constructor stub
    }

    public UserAccountException(String message) {
        super(message);
        // TODO Auto-generated constructor stub
    }

    public UserAccountException(Throwable cause) {
        super(cause);
        // TODO Auto-generated constructor stub
    }

    
    
}

要定义自己异常的名称，需要让其继承RuntimeException，并实现构造方法。

然后是服务层的代码：

BookShopService.java

package com.gong.spring.tx;

public interface BookShopService {
    
    public void purchase(String username, String isbn);
    
}

只有一个方法体，就是购买的操作。

BookShopServiceImpl.java　　

package com.gong.spring.tx;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;


@Service("bookShopService")
public class BookShopServiceImpl implements BookShopService {

    @Autowired
    private BookShopDao bookShopDao;
    
    @Override
    public void purchase(String username, String isbn) {
        
        //1. 获取书的单价
        int price = bookShopDao.findBookPriceByIsbn(isbn);
        
        //2. 更新库存
        bookShopDao.updateBookStock(isbn);
        
        //3. 更新余额
        bookShopDao.updateUserAccount(username, price);
    }

}

最后，我们建立一个JUnit Test Case的文件进行测试：

SpringTransactionImpl.java

package com.gong.spring.tx;

import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class SpringTransactionTest {

    private ApplicationContext ctx = null;
    private BookShopDao bookShopDao = null;
    private BookShopService bookShopService = null;
    {
        ctx = new ClassPathXmlApplicationContext("applicationContext.xml");
        bookShopDao = ctx.getBean(BookShopDao.class);
        bookShopService = ctx.getBean(BookShopService.class);
    }
    
    
    @Test
    public void testBookShopService(){
        bookShopService.purchase("AA", "1001");
    }
    
    @Test
    public void testBookShopDaoUpdateUserAccount(){
        bookShopDao.updateUserAccount("AA", 10);
    }
    
    @Test
    public void testBookShopDaoUpdateBookStock(){
        bookShopDao.updateBookStock("1001");
    }
    
    @Test
    public void testBookShopDaoFindPriceByIsbn() {
        System.out.println(bookShopDao.findBookPriceByIsbn("1001"));
    }

}