首页 > > 网络编程 > Mysql >

MySQL的事务

2018-06-23 13:28:57来源：未知阅读 ()

一、事务概述

1．什么是事务

一件事情有n个组成单元要不这n个组成单元同时成功要不n个单元就同时失败

就是将n个组成单元放到一个事务中

2．mysql的事务

默认的事务：一条sql语句就是一个事务默认就开启事务并提交事务

手动事务：

1）显示的开启一个事务：start transaction

2）事务提交：commit代表从开启事务到事务提交中间的所有的sql都认为有效真正的更新数据库

3）事务的回滚：rollback 代表事务的回滚从开启事务到事务回滚中间的所有的 sql操作都认为无效数据库没有被更新

二、JDBC事务操作

默认是自动事务：

执行sql语句：executeUpdate() ---- 每执行一次executeUpdate方法代表事务自动提交

通过jdbc的API手动事务：

开启事务：conn.setAutoComnmit(false);

提交事务：conn.commit();

回滚事务：conn.rollback();

注意：控制事务的connnection必须是同一个

执行sql的connection与开启事务的connnection必须是同一个才能对事务进行控制

示例：

package jdbc;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;

public class JDBCDemo {
    public static void main(String[] args) {
        Connection conn = null;
        try {
            // 注册驱动
            Class.forName("com.mysql.jdbc.Driver");
            // 获得连接
            conn = DriverManager.getConnection("jdbc:mysql:///web", "root", "xuyiqing");
            //开启事务
            conn.setAutoCommit(false);//false表示不自动提交
            // 获得执行平台
            Statement stmt = conn.createStatement();            
            // 执行sql
            stmt.executeUpdate("update user set password=123456 where username=zhangsan");
            //提交事务
            conn.commit();
            
            stmt.close();
            conn.close();
        } catch (Exception e) {
            try {
                conn.rollback();
            } catch (SQLException e1) {
                e1.printStackTrace();
            }
            e.printStackTrace();
        }
    }
}

View Code

三、DBUtils事务操作

1．QueryRunner

有参构造：QueryRunner runner = new QueryRunner(DataSource dataSource);

有参构造将数据源(连接池)作为参数传入QueryRunner，QueryRunner会从连接池中获得一个数据库连接资源操作数据库，所以直接使用无Connection参数的update方法即可操作数据库

无参构造：QueryRunner runner = new QueryRunner();

无参的构造没有将数据源（连接池）作为参数传入QueryRunner，那么我们在使用QueryRunner对象操作数据库时要使用有Connection参数的方法

示例：

package dbutils;

import java.sql.Connection;
import java.sql.SQLException;

import org.apache.commons.dbutils.QueryRunner;

import utils.DataSourceUtils;

public class DBUtilsDemo {
    public static void main(String[] args) {
        Connection conn = null;
        try {
            // 无参构造
            QueryRunner runner = new QueryRunner();
            // 获得连接
            conn = DataSourceUtils.getConnection();
            // 开启事务
            conn.setAutoCommit(false);
            runner.update(conn, "update user set password=123456 where username=zhangsan");
            // 提交或回滚事务
            conn.commit();
        } catch (Exception e) {
            try {
                conn.rollback();
            } catch (SQLException e1) {
                e1.printStackTrace();
            }
        }
    }
}

View Code

工具类:

package utils;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

import javax.sql.DataSource;

import com.mchange.v2.c3p0.ComboPooledDataSource;

public class DataSourceUtils {

    private static DataSource dataSource = new ComboPooledDataSource();

    private static ThreadLocal<Connection> tl = new ThreadLocal<Connection>();

    // 直接可以获取一个连接池
    public static DataSource getDataSource() {
        return dataSource;
    }
    
    public static Connection getConnection() throws SQLException{
        return dataSource.getConnection();
    }

    // 获取连接对象
    public static Connection getCurrentConnection() throws SQLException {

        Connection con = tl.get();
        if (con == null) {
            con = dataSource.getConnection();
            tl.set(con);
        }
        return con;
    }

    // 开启事务
    public static void startTransaction() throws SQLException {
        Connection con = getCurrentConnection();
        if (con != null) {
            con.setAutoCommit(false);
        }
    }

    // 事务回滚
    public static void rollback() throws SQLException {
        Connection con = getCurrentConnection();
        if (con != null) {
            con.rollback();
        }
    }

    // 提交并且 关闭资源及从ThreadLocall中释放
    public static void commitAndRelease() throws SQLException {
        Connection con = getCurrentConnection();
        if (con != null) {
            con.commit(); // 事务提交
            con.close();// 关闭资源
            tl.remove();// 从线程绑定中移除
        }
    }

    // 关闭资源方法
    public static void closeConnection() throws SQLException {
        Connection con = getCurrentConnection();
        if (con != null) {
            con.close();
        }
    }

    public static void closeStatement(Statement st) throws SQLException {
        if (st != null) {
            st.close();
        }
    }

    public static void closeResultSet(ResultSet rs) throws SQLException {
        if (rs != null) {
            rs.close();
        }
    }

}

View Code

案例：简单的转账代码：

代码实现：

页面transfer.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    <form action="${pageContext.request.contextPath }/transfer" method="post">
        转出账户：<input type="text" name="out"><br>
        转入账户：<input type="text" name="in"><br>
        转账金额：<input type="text" name="money"><br>
        <input type="submit" value="确认转账"><br>
    </form>
</body>
</html>

View Code

web层：

package transfer.web;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import transfer.service.TransferService;

public class TransferServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        
        //接受转账的参数
        String out = request.getParameter("out");
        String in = request.getParameter("in");
        String moneyStr = request.getParameter("money");
        double money = Double.parseDouble(moneyStr);
        
        //调用业务层的转账方法
        TransferService service = new TransferService();
        boolean isTransferSuccess = service.transfer(out,in,money);
        
        response.setContentType("text/html;charset=UTF-8");
        
        if(isTransferSuccess){
            response.getWriter().write("转账成功！！！");
        }else{
            response.getWriter().write("转账失败！！！");
        }
        
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request, response);
    }
}

View Code

service层：

package transfer.service;

import java.sql.SQLException;

import transfer.dao.TransferDao;
import utils.MyDataSourceUtils;

public class TransferService {

    public boolean transfer(String out, String in, double money) {
        
        TransferDao dao = new TransferDao();
        
        boolean isTranferSuccess = true;
        try {
            //开启事务
            MyDataSourceUtils.startTransaction();
            //转出前的方法
            dao.out(out,money);
            //转入钱的方法
            dao.in(in,money);
            
        } catch (Exception e) {
            isTranferSuccess = false;
            //回滚事务
            try {
                MyDataSourceUtils.rollback();
            } catch (SQLException e1) {
                e1.printStackTrace();
            }
            e.printStackTrace();
        } finally{
            try {
                MyDataSourceUtils.commit();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        
        return isTranferSuccess;
        
    }

}

View Code

dao层：

package transfer.dao;

import java.sql.Connection;
import java.sql.SQLException;

import org.apache.commons.dbutils.QueryRunner;

import utils.MyDataSourceUtils;

public class TransferDao {

    public void out(String out, double money) throws SQLException {
        QueryRunner runner = new QueryRunner();
        Connection conn = MyDataSourceUtils.getCurrentConnection();
        String sql = "update account set money=money-? where name=?";
        runner.update(conn, sql, money, out);
    }

    public void in(String in, double money) throws SQLException {
        QueryRunner runner = new QueryRunner();
        Connection conn = MyDataSourceUtils.getCurrentConnection();
        String sql = "update account set money=money+? where name=?";
        runner.update(conn, sql, money, in);
    }

}

View Code

工具类：

package utils;

import java.sql.Connection;
import java.sql.SQLException;

import com.mchange.v2.c3p0.ComboPooledDataSource;

public class MyDataSourceUtils {

    //获得Connection ----- 从连接池中获取
    private static ComboPooledDataSource dataSource = new ComboPooledDataSource();
    
    //创建ThreadLocal
    private static ThreadLocal<Connection> tl = new ThreadLocal<Connection>();
    
    //开启事务
    public static void startTransaction() throws SQLException{
        Connection conn = getCurrentConnection();
        conn.setAutoCommit(false);
    }
    
    //获得当前线程上绑定的conn
    public static Connection getCurrentConnection() throws SQLException{
        //从ThreadLocal寻找 当前线程是否有对应Connection
        Connection conn = tl.get();
        if(conn==null){
            //获得新的connection
            conn = getConnection();
            //将conn资源绑定到ThreadLocal（map）上
            tl.set(conn);
        }
        return conn;
    }
    
    public static Connection getConnection() throws SQLException{
        return dataSource.getConnection();
    }

    //回滚事务
    public static void rollback() throws SQLException {
        getCurrentConnection().rollback();
    }

    //提交事务
    public static void commit() throws SQLException {
        Connection conn = getCurrentConnection();
        conn.commit();
        //将Connection从ThreadLocal中移除
        tl.remove();
        conn.close();
        
    }

}