java中事务是什么？
事务是访问数据库的一个操作序列，DB应用系统通过事务集来完成对数据的存取。
事务必须遵循4个原则，即常说的 ACID
A，Automicity，原子性，即事务要么被全部执行，要么被全部不执行。如果事务下的子事务全部提交成功，则所有数据库操作被提交，否则，应进行事务回滚。
C，Consistency，一致性，即状态转换必须是由一种正确的状态转换到另外一种正确的状态。
I，Isolation，隔离性，即相互间必须不能被影响。
D，Durabillity，持久性，即事务提交后将被永久保存，即便出现其他故障，事务处理结果也应得到保存。
事务的隔离级别
串行化，Serializable，一个事务在执行过程中完全看不到其他事务对数据库所做的更新。
可重复读，Repeatable Read，一个事务在执行过程中可以看到其他事务已经提交的记录，但是不能看到其他事务对已有记录的更新。
读已提交数据，Read Commited，一个事务在执行过程中可以看到其他事务已经提交的记录，而且能看到其他事务对已有记录的更新。
读未提交数据，Read UnCommited，一个事务在执行过程中可以看到其他事务没有提交的记录，而且能看到其他事务没有提交的记录的更新
简单介绍完事务之后，我们用一个例子来具体使用一下事务：购买股票的案例
第一步：准备工作
1）数据表
股票表：stock
账户余额表：account
2）实体类
Account类
package demo22tx.entity;
/**
* Created by mycom on 2018/3/15.
*/
public class Account {
private Integer aid;
private String aname;
public Integer getAid() {
return aid;
}
public void setAid(Integer aid) {
this.aid = aid;
}
public String getAname() {
return aname;
}
public void setAname(String aname) {
this.aname = aname;
}
public Integer getAblance() {
return ablance;
}
public void setAblance(Integer ablance) {
this.ablance = ablance;
}
private Integer ablance;
}
Stock类
package demo22tx.entity;
import javax.jnlp.IntegrationService;
/**
* Created by mycom on 2018/3/15.
*/
public class Stock {
private Integer sid;
private String sname;
private Integer scount;
public Integer getSid() {
return sid;
}
public void setSid(Integer sid) {
this.sid = sid;
}
public String getSname() {
return sname;
}
public void setSname(String sname) {
this.sname = sname;
}
public Integer getScount() {
return scount;
}
public void setScount(Integer scount) {
this.scount = scount;
}
}
3）dao层
AccountDao接口
package demo22tx.dao;
/**
* Created by mycom on 2018/3/15.
*/
public interface IAccountDao {
public boolean updateAccount(int aid,int ablance,boolean isbuy);
}
AccountDaoImpl实现类
package demo22tx.dao;
import org.springframework.jdbc.core.support.JdbcDaoSupport;
/**
* Created by mycom on 2018/3/15.
*/
public class AccountDaoImpl extends JdbcDaoSupport implements IAccountDao {
public boolean updateAccount(int aid, int ablance, boolean isbuy) {
String sql="";
boolean flag=false;
if(isbuy){
//买入购票
sql="update account set balance=balance-? where aid=?";
}else{
sql="update account set balance=balance+? where aid=?";
}
int update = this.getJdbcTemplate().update(sql, ablance, aid);
if(update>0){
flag=true;
}
return flag;
}
}
StockDao接口
package demo22tx.dao;
/**
* Created by mycom on 2018/3/15.
*/
public interface IStockDao {
public boolean updateStock(int sid,int count,boolean isbuy);
}
StockDaoImpl实现类
package demo22tx.dao;
import org.springframework.jdbc.core.support.JdbcDaoSupport;
/**
* Created by mycom on 2018/3/15.
*/
public class StockDaoImpl extends JdbcDaoSupport implements IStockDao {
public boolean updateStock(int sid, int count, boolean isbuy) {
String sql="";
boolean flag=false;
if(isbuy){
//买入购票
sql="update stock set count=count+? where sid=?";
}else{
sql="update stock set count=count+? where sid=?";
}
int update = this.getJdbcTemplate().update(sql, count, sid);
if(update>0){
flag=true;
}
return flag;
}
}
4）service层
IStockService接口
package demo22tx.service;
import demo22tx.entity.StockException;
import org.springframework.transaction.annotation.Transactional;
/**
* Created by mycom on 2018/3/15.
*/
public interface IStockService {
public boolean buyStock(int aid,int abalance,int sid,int count) throws StockException;
}
StockServiceImpl实现类
package demo22tx.service;
import demo22tx.dao.IAccountDao;
import demo22tx.dao.IStockDao;
import demo22tx.entity.StockException;
import org.springframework.transaction.annotation.Transactional;
/**
* Created by mycom on 2018/3/15.
*/
public class StockServiceImpl implements IStockService{
private IAccountDao accountDao;
private IStockDao stockDao;
@Transactional
public boolean buyStock(int aid, int abalance, int sid, int count) throws StockException {
boolean isbuy=true;
//异常
if(1==1){
throw new StockException("出错了");
}
boolean account = accountDao.updateAccount(aid, abalance, isbuy);
boolean stock = stockDao.updateStock(sid, count, isbuy);
if(account&&stock){
return true;
}else{
return false;
}
}
public IAccountDao getAccountDao() {
return accountDao;
}
public void setAccountDao(IAccountDao accountDao) {
this.accountDao = accountDao;
}
public IStockDao getStockDao() {
return stockDao;
}
public void setStockDao(IStockDao stockDao) {
this.stockDao = stockDao;
}
}
第二步：配置文件
JDBC.properties文件
jdbc.driver=com.mysql.jdbc.Driver jdbc.url=jdbc:mysql:///s2228 jdbc.username=root jdbc.password=
applicationContextdemo22tx.xml文件
<?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:aop="http://www.springframework.org/schema/aop"
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/aop http://www.springframework.org/schema/aop/spring-aop.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx.xsd">
<!--配置数据源-->
<bean id="dateSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
<property name="driverClassName" value="${jdbc.driver}"></property>
<property name="url" value="${jdbc.url}"></property>
<property name="username" value="${jdbc.username}"></property>
<property name="password" value="${jdbc.password}"></property>
</bean>
<!--识别到jdbc.properties-->
<!--配置1-->
<!--<context:property-placeholder location="classpath:jdbc.properties"></context:property-placeholder>-->
<!--配置2-->
<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
<property name="location" value="classpath:jdbc.properties"></property>
</bean>
<!--配置Dao-->
<bean id="accountDao" class="demo22tx.dao.AccountDaoImpl">
<property name="dataSource" ref="dateSource"></property>
</bean>
<bean id="stockDao" class="demo22tx.dao.StockDaoImpl">
<property name="dataSource" ref="dateSource"></property>
</bean>
<!--service id-->
<bean id="stockService" class="demo22tx.service.StockServiceImpl">
<property name="accountDao" ref="accountDao"></property>
<property name="stockDao" ref="stockDao"></property>
</bean>
<!--事务-->
<!--事务管理器-->
<bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
<property name="dataSource" ref="dateSource"></property>
</bean>
<!--事务代理工厂bean 方式一-->
<!--<bean id="stockServiceProxy" class="org.springframework.transaction.interceptor.TransactionProxyFactoryBean">-->
<!--<property name="transactionManager" ref="transactionManager"></property>-->
<!--<property name="target" ref="stockService"></property>-->
<!--<property name="transactionAttributes">-->
<!--<props>-->
<!--<prop key="buyStock">ISOLATION_DEFAULT,PROPAGATION_REQUIRED</prop>-->
<!--</props>-->
<!--</property>-->
<!--</bean>-->
<!--事务代理工厂bean 方式二-->
<!--<tx:annotation-driven transaction-manager="transactionManager"></tx:annotation-driven>-->
<!--事务代理工厂bean 方式三-->
<tx:advice id="stockAdvice" transaction-manager="transactionManager">
<tx:attributes>
<tx:method name="buyStock" isolation="DEFAULT" propagation="REQUIRED"/>
</tx:attributes>
</tx:advice>
<aop:config>
<aop:pointcut id="mypointcut" expression="execution(* demo22tx.service.*.*(..))"></aop:pointcut>
<aop:advisor advice-ref="stockAdvice" pointcut-ref="mypointcut"></aop:advisor>
</aop:config>
</beans>
第三步：测试类
import demo21.entity.Book;
import demo21.service.IBookservice;
import demo22tx.entity.StockException;
import demo22tx.service.IStockService;
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import java.util.List;
/**
* Created by mycom on 2018/3/3.
*/
public class TestTrasaction20180315 {
//JDBCtemplate测试类
@Test
public void t1() throws StockException {
ApplicationContext context = new ClassPathXmlApplicationContext("applicationContextdemo22tx.xml");
IStockService stockService =(IStockService) context.getBean("stockService");
stockService.buyStock(1,100,1,10);
}
}