事务（转账实例）

本文转载自查看原文 2019-06-26 09:45 683 转账

事务（以转账为例）

事务:
　　就是一件完整的事情,包含多个操作单元,这些操作要么全部成功,要么全部失败.
　　例如:转账，包含转出操作和转入操作.

mysql中的事务: mysql中事务默认是自动提交,一条sql语句就是一个事务. 开启手动事务方式 方式1:关闭自动事务.(了解) set autocommit = off; 方式2:手动开启一个事务.(理解) start transaction;-- 开启一个事务 commit;-- 事务提交 rollback;-- 事务回滚 扩展: oracle中事务默认是手动的,必须手动提交才可以.

 java中的事务: Connection接口的api:★ setAutoCommit(false);//手动开启事务
 commit():事务提交 rollback():事务回滚 扩展:了解 Savepoint还原点 void rollback(Savepoint savepoint) :还原到那个还原点 Savepoint setSavepoint() :设置还原点

例如:创建数据库和表 create database hjh; use hjh; create table account( name varchar(20), money int ); insert into account values('hejh','1000'); insert into account values('swy','1000'); 完成 hejh给swy转500; update account set money = money - 100 where name=''; update account set money = money + 100 where name='swy';

转账案例：

步骤分析: 1.数据库和表 2.新建一个项目 transfer 3.导入jar包和工具类 驱动 jdbcUtils c3p0及其配置文件和工具类 dbutils 4.新建一个account.jsp 表单 5.accountservlet: 接受三个参数 调用accountservice.account方法完成转账操作 打印信息 6.account方法中: 使用jdbc不考虑事务 调用dao完成转出操作 调用dao完成转入操作 7.dao中

代码实现：

　　web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" 
　　xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" 
　　　　　　id="WebApp_ID" version="3.1">
  <servlet>
      <servlet-name>AccountServlet</servlet-name>
      <servlet-class>com.hjh.servlet.AccountServlet</servlet-class>
  </servlet>
  <servlet-mapping>
      <servlet-name>AccountServlet</servlet-name>
      <url-pattern>/account</url-pattern>
  </servlet-mapping>
</web-app>

　　account.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>转账页面</title>
</head>
<body>
    <form action="${pageContext.request.contextPath }/account" method="post">
        <table border="1" width="400">
            <tr>
                <td>付款人:</td>
                <td><input type="text" name="fromUser"/></td>
            </tr>
            <tr>
                <td>收款人:</td>
                <td><input type="text" name="toUser"/></td>
            </tr>
            <tr>
                <td>转账金额:</td>
                <td><input type="text" name="money"/></td>
            </tr>
            <tr>
                <td colspan="2"><input type="submit" value="转账"/></td>
            </tr>
        </table>
    </form>
</body>
</html>

AccountServlet.java

package com.hjh.servlet; import java.io.IOException; import java.io.PrintWriter; import java.sql.SQLException; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import com.hjh.service.AccountService; /** * 转账案例 */
public class AccountServlet extends HttpServlet { private static final long serialVersionUID = 1L; protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //设置编码
        request.setCharacterEncoding("utf-8"); response.setContentType("text/html; charset=utf-8"); //获取输出流
        PrintWriter w = response.getWriter(); //接收jsp页面传来的三个参数
        String fromUser = request.getParameter("fromUser"); String toUser = request.getParameter("toUser"); int money = Integer.parseInt(request.getParameter("money")); //调用AccountService的transterAccount(fromUser，toUser，money)方法
        try { new AccountService().transterAccount(fromUser,toUser,money); } catch (Exception e) { e.printStackTrace(); w.println("转账失败"); return; } //打印提示信息
        w.print("转账成功"); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } }

　　AccountService.java

package com.hjh.service; import java.sql.SQLException; import com.hjh.dao.AccountDao; public class AccountService { public void transterAccount(String fromUser, String toUser, int money) throws Exception { AccountDao dao = new AccountDao(); //转出方，出钱
 dao.accountFrom(fromUser,money); //转入方，进钱
 dao.accountTo(toUser,money); } }

　　AccountDao.java

package com.hjh.dao; import java.sql.Connection; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; import com.hjh.utils.JDBCUtil; public class AccountDao { //出账
    public void accountFrom(String fromUser, int money) throws SQLException { Connection conn = null; PreparedStatement st = null; try { //获取连接
            conn = JDBCUtil.getConnection(); //编写sql
            String sql="update account set money = money - ?  where name = ?"; //获取sql语句执行者
            st = conn.prepareStatement(sql); //设置sql参数
            st.setInt(1, money); st.setString(2, fromUser); //执行sql
            int i = st.executeUpdate(); System.out.println("转出钱成功"+i); } catch (SQLException e) { e.printStackTrace(); throw e; }finally { JDBCUtil.closeResourse(conn, st); } } //入账
    public void accountTo(String toUser, int money) throws SQLException { Connection conn = null; PreparedStatement st = null; try { //获取连接
            conn = JDBCUtil.getConnection(); //编写sql
            String sql="update account set money = money + ?  where name = ?"; //获取sql语句执行者
            st = conn.prepareStatement(sql); //设置sql参数
            st.setInt(1, money); st.setString(2, toUser); //执行sql
            int i = st.executeUpdate(); System.out.println("转入钱成功"+i); } catch (SQLException e) { e.printStackTrace(); throw e; } finally { JDBCUtil.closeResourse(conn, st); } } }

　　JDBCUtil.java

package com.hjh.utils; import java.sql.Connection; import java.sql.DriverManager; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement; public class JDBCUtil { final static String driver = "com.mysql.jdbc.Driver"; final static String url = "jdbc:mysql://localhost/hjh?useUnicode=true&characterEncoding=UTF-8"; final static String user  = "root"; final static String password = "root"; Connection conn = null; PreparedStatement ps = null; Statement st = null; ResultSet rs = null; /**获取连接*/
    public static Connection getConnection() throws SQLException { Connection conn = null; try { //注册驱动
 Class.forName(driver); //获取连接
            conn = DriverManager.getConnection(url, user, password); } catch (ClassNotFoundException e) { e.printStackTrace(); } return conn; } /**关闭资源closeResourse（conn,st）*/
    public static void closeResourse(Connection conn,Statement st) { try { if(st!=null) { st.close(); }else { st = null; } } catch (SQLException e) { e.printStackTrace(); } try { if(conn!=null) { conn.close(); }else { conn = null; } } catch (SQLException e) { e.printStackTrace(); } } /**关闭资源closeResourse（conn,ps）*/
    public static void closeResourse(Connection conn,PreparedStatement ps) { try { if(ps!=null) { ps.close(); }else { ps = null; } } catch (SQLException e) { e.printStackTrace(); } try { if(conn!=null) { conn.close(); }else { conn = null; } } catch (SQLException e) { e.printStackTrace(); } } /**关闭资源closeResourse（rs）*/
    public static void closeResourse(ResultSet rs) { try { if(rs!=null) { rs.close(); }else { rs = null; } } catch (SQLException e) { e.printStackTrace(); } } }

　　启动项目，进行转账，不发生异常的时候，转账是成功的，

转账前：

　　转账后：

一旦出现异常,钱飞了.

　　模拟断电：

　　 accountService,java中加一个异常，模拟断电的场景：

package com.hjh.service; import java.sql.SQLException; import com.hjh.dao.AccountDao; public class AccountService { public void transterAccount(String fromUser, String toUser, int money) throws Exception { AccountDao dao = new AccountDao(); //转出方，出钱
 dao.accountFrom(fromUser,money); int i=3/0; //转入方，进钱
 dao.accountTo(toUser,money); } }

　　转账前：

　　转账但是中途发生断电后，转账失败，但是在查询数据库之后发现，转出方的钱被扣了，但是转入方的钱不变，这样就会造成很重大的影响：

一旦出现异常,钱飞了. 要想避免这事情,必须添加事务,在service添加事务. 为了保证所有的操作在一个事务中,必须保证使用的是同一个连接 在service层我们获取了连接,开启了事务.如何dao层使用此连接呢????

方法1:
            向下传递参数.注意连接应该在service释放

　　accountDao.java

package com.hjh.dao; import java.sql.Connection; import java.sql.PreparedStatement; import java.sql.SQLException; import com.hjh.utils.JDBCUtil; public class AccountDao { //出账
    public void accountFrom(Connection conn, String fromUser, int money) throws SQLException { PreparedStatement st = null; try { //编写sql
            String sql="update account set money = money - ?  where name = ?"; //获取sql语句执行者
            st = conn.prepareStatement(sql); //设置sql参数
            st.setInt(1, money); st.setString(2, fromUser); //执行sql
            int i = st.executeUpdate(); System.out.println("转出钱成功"+i); } catch (SQLException e) { //e.printStackTrace();
            throw e; }finally { JDBCUtil.closeStatement(st); } } //入账
    public void accountTo(Connection conn, String toUser, int money) throws SQLException { PreparedStatement st = null; try { //编写sql
            String sql="update account set money = money + ?  where name = ?"; //获取sql语句执行者
            st = conn.prepareStatement(sql); //设置sql参数
            st.setInt(1, money); st.setString(2, toUser); //执行sql
            int i = st.executeUpdate(); System.out.println("转入钱成功"+i); } catch (SQLException e) { //e.printStackTrace();
            throw e; } finally { JDBCUtil.closePreparedStatement(st); } } }

　　accountService.java

package com.hjh.service; import java.sql.Connection; import com.hjh.dao.AccountDao; import com.hjh.utils.JDBCUtil; public class AccountService { public void transterAccount(String fromUser, String toUser, int money) throws Exception { Connection conn = null; AccountDao dao = new AccountDao(); //开启事务
            try { conn = JDBCUtil.getConnection(); conn.setAutoCommit(false);//设置事务为手动提交 //转出方，出钱
 dao.accountFrom(conn,fromUser,money); int i=3/0; //转入方，进钱
 dao.accountTo(conn,toUser,money); //事务提交
 conn.commit(); } catch (Exception e) { //e.printStackTrace(); //事务回滚
 conn.rollback(); throw e; }finally { JDBCUtil.closeConnection(conn); } } }

　　accountServlet.java

package com.hjh.servlet; import java.io.IOException; import java.io.PrintWriter; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import com.hjh.service.AccountService; /** * 转账案例 * 解决中途断电问题： * 方法1: 向下传递参数.注意连接应该在service释放 */
public class AccountServlet extends HttpServlet { private static final long serialVersionUID = 1L; protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //设置编码
        request.setCharacterEncoding("utf-8"); response.setContentType("text/html; charset=utf-8"); //获取输出流
        PrintWriter w = response.getWriter(); //接收jsp页面传来的三个参数
        String fromUser = request.getParameter("fromUser"); String toUser = request.getParameter("toUser"); int money = Integer.parseInt(request.getParameter("money")); //调用AccountService的transterAccount(fromUser，toUser，money)方法
        try { new AccountService().transterAccount(fromUser,toUser,money); } catch (Exception e) { e.printStackTrace(); w.println("转账失败"); return; } //打印提示信息
        w.print("转账成功"); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } }

　　JDBCUtil.java

package com.hjh.utils; import java.sql.Connection; import java.sql.DriverManager; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement; public class JDBCUtil { final static String driver = "com.mysql.jdbc.Driver"; final static String url = "jdbc:mysql://localhost/hjh?useUnicode=true&characterEncoding=UTF-8"; final static String user  = "root"; final static String password = "root"; Connection conn = null; PreparedStatement ps = null; Statement st = null; ResultSet rs = null; /**获取连接*/
    public static Connection getConnection() throws SQLException { Connection conn = null; try { //注册驱动
 Class.forName(driver); //获取连接
            conn = DriverManager.getConnection(url, user, password); } catch (ClassNotFoundException e) { e.printStackTrace(); } return conn; } public static void closeConnection_Statement_ResultSet(Connection conn,Statement st,ResultSet rs) { closeResultSet(rs); closeStatement(st); closeConnection(conn); } public static void closeConnection_Statement(Connection conn,Statement st) { closeStatement(st); closeConnection(conn); } public static void closeConnection_PreparedStatement_ResultSet(Connection conn,PreparedStatement ps,
　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　ResultSet rs) { closeResultSet(rs); closePreparedStatement(ps); closeConnection(conn); } public static void closeConnection_PreparedStatement(Connection conn,PreparedStatement ps) { closePreparedStatement(ps); closeConnection(conn); } /**关闭资源 closeStatement(（st）*/
    public static void closeStatement(Statement st) { try { if(st!=null) { st.close(); }else { st = null; } } catch (SQLException e) { e.printStackTrace(); } } /**关闭资源closeResourse（conn,ps）*/
    public static void closeResourse(Connection conn,PreparedStatement ps) { closePreparedStatement(ps); closeConnection(conn); } public static void closePreparedStatement(PreparedStatement ps) { try { if(ps!=null) { ps.close(); }else { ps = null; } } catch (SQLException e) { e.printStackTrace(); } } public static void closeConnection(Connection conn) { try { if(conn!=null) { conn.close(); }else { conn = null; } } catch (SQLException e) { e.printStackTrace(); } } /**关闭资源closeResourse（rs）*/
    public static void closeResultSet(ResultSet rs) { try { if(rs!=null) { rs.close(); }else { rs = null; } } catch (SQLException e) { e.printStackTrace(); } } }

　　account.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>转账页面</title>
</head>
<body>
    <form action="${pageContext.request.contextPath }/account" method="post">
        <table border="1" width="400">
            <tr>
                <td>付款人:</td>
                <td><input type="text" name="fromUser"/></td>
            </tr>
            <tr>
                <td>收款人:</td>
                <td><input type="text" name="toUser"/></td>
            </tr>
            <tr>
                <td>转账金额:</td>
                <td><input type="text" name="money"/></td>
            </tr>
            <tr>
                <td colspan="2"><input type="submit" value="转账"/></td>
            </tr>
        </table>
    </form>
</body>
</html>

　　 accountService.java的这一行代码注释掉，即转入和转出这2个步骤中是连贯的，不存在异常中断的，转账能成功

    int i=3/0;

　　accountService.java的这一行代码不注释，转出操作完成，扣款；发生异常被捕捉，事务回滚到转账操作之前，金额不变，转账失败

 int i=3/0;

方法2: 可以将connection对象绑定当前线程上 jdk中有一个ThreadLocal类, ThreadLocal 实例通常是类中的 private static 字段， 它们希望将状态与某一个线程（例如，用户 ID 或事务 ID）相关联。

ThreadLocal的方法:
		构造:
			new ThreadLocal()
		set(Object value):将内容和当前线程绑定
		Object get():获取和当前线程绑定的内容
		remove():将当前线程和内容解绑
	内部维护了map集合
		map.put(当前线程,内容);
		map.get(当前线程)
		map.remove(当前线程)

　　AccountDao.java

package com.hjh.dao; import java.sql.Connection; import java.sql.PreparedStatement; import java.sql.SQLException; import com.hjh.utils.DataSourseUtils; public class AccountDao { //出账
    public void accountFrom( String fromUser, int money) throws Exception { Connection conn = null; PreparedStatement st = null; try { conn = DataSourseUtils.getConnection(); //编写sql
            String sql="update account set money = money - ?  where name = ?"; //获取sql语句执行者
            st = conn.prepareStatement(sql); //设置sql参数
            st.setInt(1, money); st.setString(2, fromUser); //执行sql
            int i = st.executeUpdate(); System.out.println("转出钱成功"+i); } catch (SQLException e) { e.printStackTrace(); throw e; }finally { DataSourseUtils.closeStatement(st); } } //入账
    public void accountTo( String toUser, int money) throws Exception { Connection conn = null; PreparedStatement st = null; try { conn = DataSourseUtils.getConnection(); //编写sql
            String sql="update account set money = money + ?  where name = ?"; //获取sql语句执行者
            st = conn.prepareStatement(sql); //设置sql参数
            st.setInt(1, money); st.setString(2, toUser); //执行sql
            int i = st.executeUpdate(); System.out.println("转入钱成功"+i); } catch (SQLException e) { //e.printStackTrace();
            throw e; } finally { DataSourseUtils.closeStatement(st); } } }

　　AccountService.java

package com.hjh.service; import com.hjh.dao.AccountDao; import com.hjh.utils.DataSourseUtils; public class AccountService { public void transterAccount(String fromUser, String toUser, int money) throws Exception { AccountDao dao = new AccountDao(); try { //开启事务
 DataSourseUtils.startTransaction(); //转出方，出钱
 dao.accountFrom(fromUser,money); //int i=3/0; //转入方，进钱
 dao.accountTo(toUser,money); //事务提交
 DataSourseUtils.commitAndClose(); } catch (Exception e) { e.printStackTrace(); //事务回滚
 DataSourseUtils.rollbackAndClose(); throw e; } } }

　　AccountServlet.java

package com.hjh.servlet; import java.io.IOException; import java.io.PrintWriter; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import com.hjh.service.AccountService; /** * 转账案例 * 解决中途断电问题： * 方法1: 向下传递参数.注意连接应该在service释放 */
public class AccountServlet extends HttpServlet { private static final long serialVersionUID = 1L; protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //设置编码
        request.setCharacterEncoding("utf-8"); response.setContentType("text/html; charset=utf-8"); //获取输出流
        PrintWriter w = response.getWriter(); //接收jsp页面传来的三个参数
        String fromUser = request.getParameter("fromUser"); String toUser = request.getParameter("toUser"); int money = Integer.parseInt(request.getParameter("money")); //调用AccountService的transterAccount(fromUser，toUser，money)方法
        try { new AccountService().transterAccount(fromUser,toUser,money); } catch (Exception e) { e.printStackTrace(); w.println("转账失败"); return; } //打印提示信息
        w.print("转账成功"); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } }

　　DataSourseUtils.java

package com.hjh.utils; import java.sql.Connection; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement; import javax.sql.DataSource; import com.mchange.v2.c3p0.ComboPooledDataSource; public class DataSourseUtils { //建立连接池ds
    private static ComboPooledDataSource ds =     new ComboPooledDataSource(); //将connection绑定在当前线程中
    private static ThreadLocal<Connection> tl = new ThreadLocal<>(); //获取数据源
    public static DataSource getDataSourse() { return ds; } //获取连接,从当前线程中获取
    public static Connection getConnection() throws Exception { Connection conn = tl.get(); if(conn==null) { //第一次获取，创建一个连接和当前线程绑定在一起
            conn =ds.getConnection(); //绑定
 tl.set(conn); } return conn; } //获取连接，开启事务
    public static void startTransaction() throws Exception { getConnection().setAutoCommit(false); } //事务提交|解除绑定
    public static void commitAndClose() { try { Connection conn = getConnection(); //提交事务
 conn.commit(); //解除绑定
 tl.remove(); //释放资源
 closeConnection(conn); } catch (Exception e) { e.printStackTrace(); } } //事务回滚
        public static void rollbackAndClose() { try { Connection conn = getConnection(); //提交事务
 conn.rollback(); //释放资源
 closeConnection(conn); //解除绑定
 tl.remove(); } catch (Exception e) { e.printStackTrace(); } } //释放资源connection
    public static void closeConnection(Connection conn) { try { if(conn!=null) { conn.close(); //并和当前线程解绑
 tl.remove(); } } catch (Exception e) { e.printStackTrace(); } conn = null; } //释放资源Statement
        public static void closeStatement(Statement st) { try { if(st!=null) { st.close(); }else { st = null; } } catch (SQLException e) { e.printStackTrace(); } } /**释放资源closePreparedStatement*/
        public static void closePreparedStatement(PreparedStatement ps) { try { if(ps!=null) { ps.close(); }else { ps = null; } } catch (SQLException e) { e.printStackTrace(); } } //释放资源Connection ,Statement 
    public static void close2Resourse(Connection conn,Statement st) { closeStatement(st); closeConnection(conn); } /**释放资源closeResourse（conn,ps）*/
    public static void close2Resourse(Connection conn,PreparedStatement ps) { closePreparedStatement(ps); closeConnection(conn); } /**释放资源closeResourse（rs）*/
    public static void closeResourse(ResultSet rs) { try { if(rs!=null) { rs.close(); }else { rs = null; } } catch (SQLException e) { e.printStackTrace(); } } }

　　web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation=
　　　　"http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
  <servlet>
      <servlet-name>AccountServlet</servlet-name>
      <servlet-class>com.hjh.servlet.AccountServlet</servlet-class>
  </servlet>
  <servlet-mapping>
      <servlet-name>AccountServlet</servlet-name>
      <url-pattern>/account</url-pattern>
  </servlet-mapping>
</web-app>

　　account.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>转账页面</title>
</head>
<body>
    <form action="${pageContext.request.contextPath }/account" method="post">
        <table border="1" width="400">
            <tr>
                <td>付款人:</td>
                <td><input type="text" name="fromUser"/></td>
            </tr>
            <tr>
                <td>收款人:</td>
                <td><input type="text" name="toUser"/></td>
            </tr>
            <tr>
                <td>转账金额:</td>
                <td><input type="text" name="money"/></td>
            </tr>
            <tr>
                <td colspan="2"><input type="submit" value="转账"/></td>
            </tr>
        </table>
    </form>
</body>
</html>

DButils: 1.创建queryrunner 2.编写sql 3.执行sql QueryRunner: 构造: new QueryRunner(DataSource ds):自动事务 new QueryRunner():手动事务 常用方法: update(Connection conn,String sql,Object ... params):执行的cud操作 query(Connection conn....):执行查询操作 注意: 一旦使用手动事务,调用方法的时候都需要手动传入connection,并且需要手动关闭连接

　　accountDao.java

package com.hjh.dao; import org.apache.commons.dbutils.QueryRunner; import com.hjh.utils.DataSourseUtils; public class AccountDao { //出账
    public void accountFrom( String fromUser, int money) throws Exception { QueryRunner qr = new QueryRunner(); //编写sql
            String sql="update account set money = money - ?  where name = ?"; //执行sql
 qr.update(DataSourseUtils.getConnection(),sql,money,fromUser); System.out.println("转入钱成功"); } //入账
    public void accountTo( String toUser, int money) throws Exception { QueryRunner qr = new QueryRunner(); //编写sql
        String sql="update account set money = money + ?  where name = ?"; //执行sql
 qr.update(DataSourseUtils.getConnection(),sql,money,toUser); System.out.println("转出钱成功"); } }

　　accountService.java

package com.hjh.service; import com.hjh.dao.AccountDao; import com.hjh.utils.DataSourseUtils; public class AccountService { public void transterAccount(String fromUser, String toUser, int money) throws Exception { AccountDao dao = new AccountDao(); try { //开启事务
 DataSourseUtils.startTransaction(); //转出方，出钱
 dao.accountFrom(fromUser,money); //int i=3/0; //转入方，进钱
 dao.accountTo(toUser,money); //事务提交
 DataSourseUtils.commitAndClose(); } catch (Exception e) { e.printStackTrace(); //事务回滚
 DataSourseUtils.rollbackAndClose(); throw e; } } }

　　accountServlet.java

package com.hjh.servlet; import java.io.IOException; import java.io.PrintWriter; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import com.hjh.service.AccountService; /** * 转账案例 * 解决中途断电问题： * 方法1: dbutils */
public class AccountServlet extends HttpServlet { private static final long serialVersionUID = 1L; protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //设置编码
        request.setCharacterEncoding("utf-8"); response.setContentType("text/html; charset=utf-8"); //获取输出流
        PrintWriter w = response.getWriter(); //接收jsp页面传来的三个参数
        String fromUser = request.getParameter("fromUser"); String toUser = request.getParameter("toUser"); int money = Integer.parseInt(request.getParameter("money")); //调用AccountService的transterAccount(fromUser，toUser，money)方法
        try { new AccountService().transterAccount(fromUser,toUser,money); } catch (Exception e) { e.printStackTrace(); w.println("转账失败"); return; } //打印提示信息
        w.print("转账成功"); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } }

　　DataSourceUtils.java

package com.hjh.utils; import java.sql.Connection; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement; import javax.sql.DataSource; import com.mchange.v2.c3p0.ComboPooledDataSource; public class DataSourseUtils { //建立连接池ds
    private static ComboPooledDataSource ds =     new ComboPooledDataSource(); //将connection绑定在当前线程中
    private static ThreadLocal<Connection> tl = new ThreadLocal<>(); //获取数据源
    public static DataSource getDataSourse() { return ds; } //获取连接,从当前线程中获取
    public static Connection getConnection() throws Exception { Connection conn = tl.get(); if(conn==null) { //第一次获取，创建一个连接和当前线程绑定在一起
            conn =ds.getConnection(); //绑定
 tl.set(conn); } return conn; } //获取连接，开启事务
    public static void startTransaction() throws Exception { getConnection().setAutoCommit(false); } //事务提交|解除绑定
    public static void commitAndClose() { try { Connection conn = getConnection(); //提交事务
 conn.commit(); //解除绑定
 tl.remove(); //释放资源
 closeConnection(conn); } catch (Exception e) { e.printStackTrace(); } } //事务回滚
        public static void rollbackAndClose() { try { Connection conn = getConnection(); //提交事务
 conn.rollback(); //释放资源
 closeConnection(conn); //解除绑定
 tl.remove(); } catch (Exception e) { e.printStackTrace(); } } //释放资源connection
    public static void closeConnection(Connection conn) { try { if(conn!=null) { conn.close(); //并和当前线程解绑
 tl.remove(); } } catch (Exception e) { e.printStackTrace(); } conn = null; } //释放资源Statement
        public static void closeStatement(Statement st) { try { if(st!=null) { st.close(); }else { st = null; } } catch (SQLException e) { e.printStackTrace(); } } /**释放资源closePreparedStatement*/
        public static void closePreparedStatement(PreparedStatement ps) { try { if(ps!=null) { ps.close(); }else { ps = null; } } catch (SQLException e) { e.printStackTrace(); } } //释放资源Connection ,Statement 
    public static void close2Resourse(Connection conn,Statement st) { closeStatement(st); closeConnection(conn); } /**释放资源closeResourse（conn,ps）*/
    public static void close2Resourse(Connection conn,PreparedStatement ps) { closePreparedStatement(ps); closeConnection(conn); } /**释放资源closeResourse（rs）*/
    public static void closeResourse(ResultSet rs) { try { if(rs!=null) { rs.close(); }else { rs = null; } } catch (SQLException e) { e.printStackTrace(); } } }

　　c3p0-config.xml

<c3p0-config>
    <!-- 默认配置，如果没有指定则使用这个配置 -->
    <default-config>
        <!-- 基本配置 -->
        <property name="driverClass">com.mysql.jdbc.Driver</property>
        <property name="jdbcUrl">jdbc:mysql://localhost/hjh?characterEncoding=UTF-8 </property>
        <property name="user">root</property>
        <property name="password">root</property>
    
        <!--扩展配置-->
        <property name="checkoutTimeout">30000</property>
        <property name="idleConnectionTestPeriod">30</property>
        <property name="initialPoolSize">10</property>
        <property name="maxIdleTime">30</property>
        <property name="maxPoolSize">100</property>
        <property name="minPoolSize">10</property>
        <property name="maxStatements">200</property>
    </default-config> 
    
    
    <!-- 命名的配置 -->
    <named-config name="XXX">
        <property name="driverClass">com.mysql.jdbc.Driver</property>
        <property name="jdbcUrl">jdbc:mysql://127.0.0.1:3306/xxxx</property>
        <property name="user">root</property>
        <property name="password">1234</property>
        
        
        <!-- 如果池中数据连接不够时一次增长多少个 -->
        <property name="acquireIncrement">5</property>
        <property name="initialPoolSize">20</property>
        <property name="minPoolSize">10</property>
        <property name="maxPoolSize">40</property>
        <property name="maxStatements">20</property>
        <property name="maxStatementsPerConnection">5</property>
    </named-config>
</c3p0-config>

　　account.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>转账页面</title>
</head>
<body>
    <form action="${pageContext.request.contextPath }/account" method="post">
        <table border="1" width="400">
            <tr>
                <td>付款人:</td>
                <td><input type="text" name="fromUser"/></td>
            </tr>
            <tr>
                <td>收款人:</td>
                <td><input type="text" name="toUser"/></td>
            </tr>
            <tr>
                <td>转账金额:</td>
                <td><input type="text" name="money"/></td>
            </tr>
            <tr>
                <td colspan="2"><input type="submit" value="转账"/></td>
            </tr>
        </table>
    </form>
</body>
</html>

事务总结:

事务的特性:★★★
        ACID
        原子性:事务里面的操作单元不可切割,要么全部成功,要么全部失败
        一致性:事务执行前后,业务状态和其他业务状态保持一致.
        隔离性:一个事务执行的时候最好不要受到其他事务的影响
        持久性:一旦事务提交或者回滚.这个状态都要持久化到数据库中
    不考虑隔离性会出现的读问题★★
        脏读:在一个事务中读取到另一个事务没有提交的数据
        不可重复读:在一个事务中,两次查询的结果不一致(针对的update操作)
        虚读(幻读):在一个事务中,两次查询的结果不一致(针对的insert操作)
    通过设置数据库的隔离级别来避免上面的问题(理解)
        read uncommitted      读未提交    上面的三个问题都会出现
        read committed      读已提交    可以避免脏读的发生
        repeatable read        可重复读    可以避免脏读和不可重复读的发生
        serializable        串行化        可以避免所有的问题

    
    了解
        演示脏读的发生:
            将数据库的隔离级别设置成 读未提交
                set session transaction isolation level read uncommitted;
            查看数据库的隔离级别
                select @@tx_isolation;
        避免脏读的发生,将隔离级别设置成  读已提交
            set session transaction isolation level read committed;
            不可避免不可重复读的发生.
        
        避免不可重复读的发生 经隔离级别设置成 可重复读
            set session transaction isolation level  repeatable read;
            
        演示串行化 可以避免所有的问题
            set session transaction isolation level  serializable;
            锁表的操作.

 四种隔离级别的效率 read uncommitted>read committed>repeatable read>serializable 四种隔离级别的安全性 read uncommitted<read committed<repeatable read<serializable

开发中绝对不允许脏读发生.
        mysql中默认级别:repeatable read
        oracle中默认级别:read committed

 java中控制隔离级别:(了解) Connection的api void setTransactionIsolation(int level) level是常量

免责声明！

本站转载的文章为个人学习借鉴使用，本站对版权不负任何法律责任。如果侵犯了您的隐私权益，请联系本站邮箱yoyou2525@163.com删除。

猜您在找 Spring AOP 事务配置（实现转账事务）事务处理-回滚（转账操作） springboot项目进行事务控制之转账案例分布式事务系列 - 解决跨库转账问题关于银行转账引发的分布式事务思考从银行转账失败到分布式事务：总结与思考以银行转账为例分析分布式事务的解决方案一次给女朋友转账引发我对分布式事务的思考事务（@Transactional注解)的用法和实例 SQL server 事务实例