在三层架构中使用事务
- 在web项目中使用ThreadLocal可以实现将线程与数据(SqlSession)之间的绑定,确保每个线程访问的数据是独立的,不会相互干扰。
- ThreadLocal底层使用的是一个map,key是线程对象,value为我们自定义的对象(SqlSession对象)
- 通过ThreadLocal的使用可以保证在一个线程中,使用的SqlSession对象始终为同一个,这样在进行事务操作时,就可以将提交事务和关闭session都放在servlet层
自己封装sqlsession工具类
public class MybatisUtils {
private static SqlSessionFactory sqlSessionFactory;
//全局的,用于分发各线程唯一session
private static ThreadLocal<SqlSession> local =new ThreadLocal<>();
static {
try {
sqlSessionFactory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream("mybatis-config.xml"));
} catch (IOException e) {
throw new RuntimeException(e);
}
}
public static SqlSession getSqlSession() throws IOException {
// 获取当前线程对应的SqlSession对象
SqlSession session = local.get();
if (session == null) {
session = sqlSessionFactory.openSession();
//将sqlSession对象绑定到当前线程上
local.set(session);
}
return sqlSessionFactory.openSession();
}
public static void closeSqlSession() {
//获取当前线程对应SqlSession对象
SqlSession session = local.get();
if (session != null) {
//若当前SqlSession对象不为空
//则关闭当前的SqlSession对象,并在ThreadLocal中移除以当前线程为key的键值对
session.close();
local.remove();
}
}
}
service层
public class CustomerServiceImpl implements CustomerService {
private CustomerDao customerDao = new CustomerDaoImpl();
@Override
public void transfer(int tId, int sId, int capital) throws IOException {
SqlSession sqlSession = MybatisUtils.getSqlSession();
int tCapital = customerDao.searchCapital(tId);
if(tCapital >= capital) {
customerDao.subCapital(tId, capital);
customerDao.addCapital(sId, capital);
}else {
System.out.println("the capital is not enough");
}
sqlSession.commit();
MybatisUtils.closeSqlSession();
}
}
dao层
public class CustomerDaoImpl implements CustomerDao {
SqlSession sqlSession;
@Override
public void subCapital(int id, int capital) throws IOException {
//由于mybatis底层获取参数是利用了get方法,故传递多个参数时,需要将其封装成一个map
sqlSession = MybatisUtils.getSqlSession();
Map<String, Object> params = new HashMap<String, Object>();
params.put("id", id);
params.put("capital", capital);
sqlSession.update("subCapital",params);
}
@Override
public void addCapital(int id, int capital) throws IOException {
sqlSession = MybatisUtils.getSqlSession();
Map<String, Object> params = new HashMap<String, Object>();
params.put("id", id);
params.put("capital", capital);
sqlSession.update("addCapital",params);
}
@Override
public int searchCapital(int id) throws IOException {
sqlSession = MybatisUtils.getSqlSession();
int capital = sqlSession.selectOne("selectCapital", id);
return capital;
}
}