1 数据库准备
1创建表
CREATE TABLE account( id INT PRIMARY KEY AUTO_INCREMENT, NAME VARCHAR(20), money DOUBLE );
2添加数据
INSERT INTO account (NAME,money) VALUES ('tom',3000),('jack',3000);
2 其它准备
1）搭建好三层架构的模型
2）导入需要的jar包
3）导入c3p0连接池配置文件
4）编写c3p0工具类
3 代码实现
1 客户端转账页面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=ISO-8859-1"> <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/> 转张金额：<input type="text" name="money"/><br/> <input type="submit" value="确认转账"/> </form> </body> </html>
2 web层TransferServlet
package www.test.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 www.test.service.TransferService; public class TransferServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // 1 获取客户端输入的数据 String out = request.getParameter("out"); String in = request.getParameter("in"); String moneyStr = request.getParameter("money"); double money = Double.parseDouble(moneyStr); // 2 调用业务层的转账方法 TransferService service = new TransferService(); boolean isTransferSuccess = service.transfer(out,in,money); // 3 将处理结果返回给用户 // 解决乱码 response.setContentType("text/html;charset=UTF-8"); // 输出结果 if(isTransferSuccess){ response.getWriter().write("恭喜你，转账成功"); }else{ response.getWriter().write("很遗憾，转账失败"); } } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } }
3 service层TransferService
package www.test.service; import java.sql.Connection; import java.sql.SQLException; import www.test.dao.TransferDao; import www.test.utils.C3P0Utils; public class TransferService { public boolean transfer(String out, String in, double money) { TransferDao dao = new TransferDao(); boolean isTranferSuccess = true; Connection conn = null; try { // 1 获取一个连接 conn = C3P0Utils.getConnection(); // 2 开启事务 conn.setAutoCommit(false); // 3 转出钱的方法 ,用flag判断操作成功 boolean flagout = dao.out(conn,out,money); // 4 转入钱的方法 boolean flagin = dao.in(conn,in,money); if(!(flagout&&flagin)){ //只要有一方失败都无效，执行回滚 isTranferSuccess = false; conn.rollback(); } } catch (SQLException e) { isTranferSuccess = false; try { // 5 回滚事务 conn.rollback(); } catch (SQLException e1) { e1.printStackTrace(); } e.printStackTrace(); }finally{ try { // 6 提交事务 // 建议放到这里，就算不成功，会回滚，回滚之后继续提交。 conn.commit(); } catch (SQLException e) { e.printStackTrace(); } } return isTranferSuccess; } }
4 dao层TransferDao
package www.test.dao; import java.sql.Connection; import java.sql.SQLException; import org.apache.commons.dbutils.QueryRunner; public class TransferDao { public boolean out(Connection conn, String out, double money) throws SQLException { QueryRunner qr = new QueryRunner(); String sql = "UPDATE account SET money=money-? WHERE NAME=?"; Object[] params = {money,out}; int num = qr.update(conn, sql, params); if(num>0){ return true; }else{ return false; } } public boolean in(Connection conn, String out, double money) throws SQLException { QueryRunner qr = new QueryRunner(); String sql = "UPDATE account SET money=money+? WHERE NAME=?"; Object[] params = {money,out}; int num = qr.update(conn, sql, params); if(num>0){ return true; }else{ return false; } } }
4 解决conn在service层的问题
1 在c3p0连接池工具类中加入事务的处理
package www.test.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 C3P0Utils { // 1 获得Connection ----- 从连接池中获取 private static DataSource dataSource = new ComboPooledDataSource(); // 2 创建ThreadLocal 存储的类型是Connection private static ThreadLocal<Connection> tl = new ThreadLocal<Connection>(); // 3 直接可以获取一个连接池 public static DataSource getDataSource() { return dataSource; } // 4 直接获取一个连接 public static Connection getConnection() throws SQLException { return dataSource.getConnection(); } // 5 获取绑定到ThreadLocal上的连接对象 public static Connection getCurrentConnection() throws SQLException { //从ThreadLocal寻找 当前线程是否有对应Connection Connection con = tl.get(); if (con == null) { //获得新的connection con = dataSource.getConnection(); //将conn资源绑定到ThreadLocal（map）上 tl.set(con); } return con; } // 6 开启事务 public static void startTransaction() throws SQLException { Connection con = getCurrentConnection(); if (con != null) { con.setAutoCommit(false); } } // 7 事务回滚 public static void rollback() throws SQLException { Connection con = getCurrentConnection(); if (con != null) { con.rollback(); } } // 8 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 } } // 9 关闭资源方法 public static void close(ResultSet rs, Statement st, Connection con) throws SQLException { if (rs != null) { rs.close(); } if (st != null) { st.close(); } if (con != null) { con.close(); } } }
2 service层代码修改完整版
package www.test.service; import java.sql.Connection; import java.sql.SQLException; import www.test.dao.TransferDao; import www.test.utils.C3P0Utils; public class TransferService{ public boolean transfer(String out, String in, double money) { TransferDao dao = new TransferDao(); boolean isTranferSuccess = true; // Connection conn = null; try { // 1 获取一个连接 // conn = C3P0Utils.getConnection(); // 2 开启事务 // conn.setAutoCommit(false); C3P0Utils.startTransaction(); // 3 转出钱的方法 ,用flag判断操作成功 // boolean flagout = dao.out(conn,out,money); boolean flagout = dao.out(out,money); // 4 转入钱的方法 // boolean flagin = dao.in(conn,in,money); boolean flagin = dao.in(in,money); if(!(flagout&&flagin)){ //只要有一方失败都无效，执行回滚 isTranferSuccess = false; // conn.rollback(); C3P0Utils.rollback(); } } catch (SQLException e) { isTranferSuccess = false; try { // 5 回滚事务 // conn.rollback(); C3P0Utils.rollback(); } catch (SQLException e1) { e1.printStackTrace(); } e.printStackTrace(); }finally{ try { // 6 提交事务 // 建议放到这里，就算不成功，会回滚，回滚之后继续提交。 // conn.commit(); //提交的时候就关闭资源，连接从线程绑定中移除 C3P0Utils.commitAndRelease(); } catch (SQLException e) { e.printStackTrace(); } } return isTranferSuccess; } }
3 dao层代码修改完整版
package www.test.dao; import java.sql.Connection; import java.sql.SQLException; import org.apache.commons.dbutils.QueryRunner; import www.test.utils.C3P0Utils; public class TransferDao { public boolean out(String out, double money) throws SQLException { // 获取的是绑定在ThreadLoacal上的conn QueryRunner qr = new QueryRunner(); Connection conn = C3P0Utils.getCurrentConnection(); String sql = "UPDATE account SET money=money-? WHERE NAME=?"; Object[] params = {money,out}; int num = qr.update(conn, sql, params); if(num>0){ return true; }else{ return false; } } public boolean in(String out, double money) throws SQLException { QueryRunner qr = new QueryRunner(); // 获取的是绑定在ThreadLoacal上的conn Connection conn = C3P0Utils.getCurrentConnection(); String sql = "UPDATE account SET money=money+? WHERE NAME=?"; Object[] params = {money,out}; int num = qr.update(conn, sql, params); if(num>0){ return true; }else{ return false; } } }