MySQL_(Java)【事物操作】使用JDBC模拟银行转账向数据库发起修改请求

　　MySQL_(Java)使用JDBC向数据库发起查询请求　　传送门

　　MySQL_(Java)使用JDBC向数据库中插入(insert)数据　　传送门

　　MySQL_(Java)使用JDBC向数据库中删除(delete)数据　　传送门

　　MySQL_(Java)使用JDBC向数据库中修改(update)数据　　传送门

　　MySQL_(Java)【连接池】简单在JDBCUtils.java中创建连接池　　传送门

数据库中事务：

　　我们之前分享数据库的数据操作，无外乎对数据库的数据进行增、删、改、查。就比如我们去买东西，一般都是先付钱，卖家收到钱再发货。这个用数据库来表示就是，第一步：从用户的账户中减去一部分金额。第二步，再把减去的金额添加到商家的账户上。

　　但是万一遇到特殊的情况，你成功的完成了第一步，从用户的数据库中扣除了钱，这时候突然停电，系统出现了故障，没有完成第二步。这就尴尬了，用户的钱少了，商家也没收到钱。

　　为了应对这种情况的发生，数据库就出现了一个功能事务，事务就是一组由 SQL 语句组成的业务逻辑，当事务内的所有 SQL语句都成功的执行，整个事务才算成功，否则就是失败。失败意味着整个的数据操作没有意义，就要把数据恢复到执行事务操作之前的状态。

　　Learn

　　　　一、未添加事务且普通转账正常 

　　　　二、在扣款和收款操作之间添加一个隐式异常

　　　　三、添加事物

数据库表结构:

　　　　

一、未添加事务且普通转账正常 　　

　　由a向b转账1000元

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 JDBC01 {

    public static void main(String[] args) throws SQLException  {
        transferAccount("a","b",1000);
    }

    public static void selectAll() throws SQLException {
        //注册驱动    使用驱动连接数据库
        Connection con = null;
        Statement stmt = null;
        ResultSet rs = null;
        try {
            //数据库的连接
            con = JDBCUtils.getConnection();
            
            //数据库的增删改查
            stmt = con.createStatement();
            //返回一个结果集
            rs =stmt.executeQuery("select * from garytb");
            
            while(rs.next()) {
                //System.out.println(rs.getString(1)+","+rs.getString(2)+","+rs.getString(3));
                System.out.println(rs.getString("id")+","+rs.getString("username")+","+rs.getString("password"));
            }
        
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally {
            JDBCUtils.close(rs, stmt, con);
        }
    }

    //校验用户
    public static boolean  selectByUernamePassword(String username,String password) throws SQLException {
        Connection con=null;
        Statement stmt = null;
        ResultSet rs = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            
            String url ="jdbc:mysql://localhost:3306/garysql?useUnicode=true&characterEncoding=UTF8&useSSL=false";
            con = DriverManager.getConnection(url,"root","123456");
            stmt =con.createStatement();
            String sql = "select * from garytb where username = '"+username+"' and password = '"+password+"'";
            //System.out.println(sql);
            rs = stmt.executeQuery(sql);
            
            if(rs.next()) {
                return true;
            }else {
                return false;
            }
                
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally {
            if(rs!=null)
                rs.close();
            if(stmt!=null)
                stmt.close();
            if(con!=null)
                con.close();
        }
        
        return false;
    }

    public static boolean selectByUP2(String username,String password) throws SQLException{
        Connection con=null;
        Statement stmt = null;
        ResultSet rs = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            
            String url ="jdbc:mysql://localhost:3306/garysql?useUnicode=true&characterEncoding=UTF8&useSSL=false";
            con = DriverManager.getConnection(url,"root","123456");
            
            String sql = "select * from garytb where username = ? and password = ?";
            PreparedStatement pstmt = con.prepareStatement(sql);
            //添加参数
            pstmt.setString(1, username);
            pstmt.setString(2, password);
            //进行查询
            rs = pstmt.executeQuery();
                
            if(rs.next()) {
                return true;
            }else {
                return false;
            }
                
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally {
            if(rs!=null)
                rs.close();
            if(stmt!=null)
                stmt.close();
            if(con!=null)
                con.close();
        }
        
        return false;
    }

    //pageNumber是页数，第几页，pageCount是每页显示多少个数据
    public static void selectUserByPage(int pageNumber,int pageCount) throws SQLException {
        //注册驱动    使用驱动连接数据库
                Connection con = null;
                PreparedStatement stmt = null;
                ResultSet rs = null;
                try {
                    Class.forName("com.mysql.jdbc.Driver");
                    
                    //String url ="jdbc:mysql://localhost:3306/garysql";
                    //指定编码查询数据库
                    String url ="jdbc:mysql://localhost:3306/garysql?useUnicode=true&characterEncoding=UTF8&useSSL=false";
                    String user = "root";
                    String password = "123456";
                    //建立和数据库的连接
                    con = DriverManager.getConnection(url,user,password);
                    
                    stmt = con.prepareStatement("select * from garytb limit ?,?");
                    stmt.setInt(1, (pageNumber-1)*pageCount );
                    stmt.setInt(2, pageCount);
                    
                    rs = stmt.executeQuery();
                    
                    while(rs.next()) {
                        //System.out.println(rs.getString(1)+","+rs.getString(2)+","+rs.getString(3));
                        System.out.println(rs.getString("id")+","+rs.getString("username")+","+rs.getString("password"));
                    }
                
                } catch (Exception e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }finally {
                    if(rs!=null)
                        rs.close();
                    if(stmt!=null)
                        stmt.close();
                    if(con!=null)
                        con.close();
                }
    }

    //crud: create read update delete
    //插入语句
    public static void insert(String username,String password) throws SQLException {
        //注册驱动    使用驱动连接数据库
        Connection con = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        try {
            con = JDBCUtils.getConnection();
            String sql = "insert into garytb(username,password) values(?,?)";
            stmt = con.prepareStatement(sql);
            stmt.setString(1, username);
            stmt.setString(2, password);
            int result =stmt.executeUpdate();// 返回值代表收到影响的行数
            System.out.println("插入成功"+username);
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally {
            JDBCUtils.close(rs, stmt, con);
        }
    }
    //删除语句
    public static void delete(int id) throws SQLException {
        //注册驱动    使用驱动连接数据库
        Connection con = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        try {
            con = JDBCUtils.getConnection();
            
            String sql = "delete from garytb where id = ?";
            stmt = con.prepareStatement(sql);
            stmt.setInt(1, id);
            int result =stmt.executeUpdate();// 返回值代表收到影响的行数
            if(result>0) {
                System.out.println("删除成功");
            }else {
                System.out.println("删除失败");
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.close(rs, stmt, con);
        }
    }
    //修改语句
    public static void update(int id,String newPassword) throws SQLException {
        Connection con = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        try {
            con = JDBCUtils.getConnection();
            
            String sql = "update garytb set password = ? where id = ?";
            stmt = con.prepareStatement(sql);
            stmt.setString(1, newPassword);
            stmt.setInt(2, id);
            int result =stmt.executeUpdate();// 返回值代表收到影响的行数
            if(result>0) {
                System.out.println("修改成功");
            }else {
                System.out.println("修改失败");
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.close(rs, stmt, con);
        }
    }

    //事物操作
    //由username1向username2转账金额
    public static void transferAccount(String username1,String username2,int money) throws SQLException {
        Connection con = null;
        PreparedStatement stmt1 = null;
        PreparedStatement stmt2 = null;
        ResultSet rs = null;
        try {
            con = JDBCUtils.getConnection();
            
            String sql = "update garytb set balance = balance - ? where username = ?";
            stmt1 = con.prepareStatement(sql);
            stmt1.setInt(1, money);
            stmt1.setString(2, username1);
            stmt1.executeUpdate();// 返回值代表收到影响的行数
            
            sql = "update garytb set balance = balance + ? where username = ?";
            stmt2 = con.prepareStatement(sql);
            stmt2.setInt(1, money);
            stmt2.setString(2, username2);
            stmt2.executeUpdate();// 返回值代表收到影响的行数
            System.out.println("操作成功！！");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.close(rs, stmt1, con);
        }
    }
    
}

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

public class JDBCUtils {
    
    private static final String connectionURL = "jdbc:mysql://localhost:3306/garysql?useUnicode=true&characterEncoding=UTF8&useSSL=false";
    private static final String username = "root";
    private static final String password = "123";
    
    //创建数据库的连接
    public static Connection getConnection() {
        try {
            Class.forName("com.mysql.jdbc.Driver");
            return   DriverManager.getConnection(connectionURL,username,password);
        } catch (Exception e) {
            
            e.printStackTrace();
        }
        return null;
    }
    
    //关闭数据库的连接
    public static void close(ResultSet rs,Statement stmt,Connection con) throws SQLException {
        if(rs!=null)
            rs.close();
        if(stmt!=null)
            stmt.close();
        if(con!=null)
            con.close();
    }
}

　　转账资源操作【资源关闭】优化版

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 JDBC01 {

    public static void main(String[] args) throws SQLException  {
        transferAccount("a","b",1000);
    }

    public static void selectAll() throws SQLException {
        //注册驱动    使用驱动连接数据库
        Connection con = null;
        Statement stmt = null;
        ResultSet rs = null;
        try {
            //数据库的连接
            con = JDBCUtils.getConnection();
            
            //数据库的增删改查
            stmt = con.createStatement();
            //返回一个结果集
            rs =stmt.executeQuery("select * from garytb");
            
            while(rs.next()) {
                //System.out.println(rs.getString(1)+","+rs.getString(2)+","+rs.getString(3));
                System.out.println(rs.getString("id")+","+rs.getString("username")+","+rs.getString("password"));
            }
        
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally {
            JDBCUtils.close(rs, stmt, con);
        }
    }

    //校验用户
    public static boolean  selectByUernamePassword(String username,String password) throws SQLException {
        Connection con=null;
        Statement stmt = null;
        ResultSet rs = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            
            String url ="jdbc:mysql://localhost:3306/garysql?useUnicode=true&characterEncoding=UTF8&useSSL=false";
            con = DriverManager.getConnection(url,"root","123456");
            stmt =con.createStatement();
            String sql = "select * from garytb where username = '"+username+"' and password = '"+password+"'";
            //System.out.println(sql);
            rs = stmt.executeQuery(sql);
            
            if(rs.next()) {
                return true;
            }else {
                return false;
            }
                
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally {
            if(rs!=null)
                rs.close();
            if(stmt!=null)
                stmt.close();
            if(con!=null)
                con.close();
        }
        
        return false;
    }

    public static boolean selectByUP2(String username,String password) throws SQLException{
        Connection con=null;
        Statement stmt = null;
        ResultSet rs = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            
            String url ="jdbc:mysql://localhost:3306/garysql?useUnicode=true&characterEncoding=UTF8&useSSL=false";
            con = DriverManager.getConnection(url,"root","123456");
            
            String sql = "select * from garytb where username = ? and password = ?";
            PreparedStatement pstmt = con.prepareStatement(sql);
            //添加参数
            pstmt.setString(1, username);
            pstmt.setString(2, password);
            //进行查询
            rs = pstmt.executeQuery();
                
            if(rs.next()) {
                return true;
            }else {
                return false;
            }
                
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally {
            if(rs!=null)
                rs.close();
            if(stmt!=null)
                stmt.close();
            if(con!=null)
                con.close();
        }
        
        return false;
    }

    //pageNumber是页数，第几页，pageCount是每页显示多少个数据
    public static void selectUserByPage(int pageNumber,int pageCount) throws SQLException {
        //注册驱动    使用驱动连接数据库
                Connection con = null;
                PreparedStatement stmt = null;
                ResultSet rs = null;
                try {
                    Class.forName("com.mysql.jdbc.Driver");
                    
                    //String url ="jdbc:mysql://localhost:3306/garysql";
                    //指定编码查询数据库
                    String url ="jdbc:mysql://localhost:3306/garysql?useUnicode=true&characterEncoding=UTF8&useSSL=false";
                    String user = "root";
                    String password = "123456";
                    //建立和数据库的连接
                    con = DriverManager.getConnection(url,user,password);
                    
                    stmt = con.prepareStatement("select * from garytb limit ?,?");
                    stmt.setInt(1, (pageNumber-1)*pageCount );
                    stmt.setInt(2, pageCount);
                    
                    rs = stmt.executeQuery();
                    
                    while(rs.next()) {
                        //System.out.println(rs.getString(1)+","+rs.getString(2)+","+rs.getString(3));
                        System.out.println(rs.getString("id")+","+rs.getString("username")+","+rs.getString("password"));
                    }
                
                } catch (Exception e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }finally {
                    if(rs!=null)
                        rs.close();
                    if(stmt!=null)
                        stmt.close();
                    if(con!=null)
                        con.close();
                }
    }

    //crud: create read update delete
    //插入语句
    public static void insert(String username,String password) throws SQLException {
        //注册驱动    使用驱动连接数据库
        Connection con = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        try {
            con = JDBCUtils.getConnection();
            String sql = "insert into garytb(username,password) values(?,?)";
            stmt = con.prepareStatement(sql);
            stmt.setString(1, username);
            stmt.setString(2, password);
            int result =stmt.executeUpdate();// 返回值代表收到影响的行数
            System.out.println("插入成功"+username);
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally {
            JDBCUtils.close(rs, stmt, con);
        }
    }
    //删除语句
    public static void delete(int id) throws SQLException {
        //注册驱动    使用驱动连接数据库
        Connection con = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        try {
            con = JDBCUtils.getConnection();
            
            String sql = "delete from garytb where id = ?";
            stmt = con.prepareStatement(sql);
            stmt.setInt(1, id);
            int result =stmt.executeUpdate();// 返回值代表收到影响的行数
            if(result>0) {
                System.out.println("删除成功");
            }else {
                System.out.println("删除失败");
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.close(rs, stmt, con);
        }
    }
    //修改语句
    public static void update(int id,String newPassword) throws SQLException {
        Connection con = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        try {
            con = JDBCUtils.getConnection();
            
            String sql = "update garytb set password = ? where id = ?";
            stmt = con.prepareStatement(sql);
            stmt.setString(1, newPassword);
            stmt.setInt(2, id);
            int result =stmt.executeUpdate();// 返回值代表收到影响的行数
            if(result>0) {
                System.out.println("修改成功");
            }else {
                System.out.println("修改失败");
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.close(rs, stmt, con);
        }
    }

    //事物操作
    //由username1向username2转账金额
    public static void transferAccount(String username1,String username2,int money) throws SQLException {
        Connection con = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        try {
            con = JDBCUtils.getConnection();
            
            String sql = "update garytb set balance = balance - ? where username = ?";
            stmt = con.prepareStatement(sql);
            stmt.setInt(1, money);
            stmt.setString(2, username1);
            stmt.executeUpdate();// 返回值代表收到影响的行数
            
            sql = "update garytb set balance = balance + ? where username = ?";
            stmt = con.prepareStatement(sql);
            stmt.setInt(1, money);
            stmt.setString(2, username2);
            stmt.executeUpdate();// 返回值代表收到影响的行数
            System.out.println("操作成功！！");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.close(rs, stmt, con);
        }
    }
    
}

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;

public class JDBCUtils {
    
    private static final String connectionURL = "jdbc:mysql://localhost:3306/garysql?useUnicode=true&characterEncoding=UTF8&useSSL=false";
    private static final String username = "root";
    private static final String password = "123";
    
    private static ArrayList<Connection> conList = new ArrayList<Connection>();
    
    static {
        for(int i =0;i<5;i++) {
            Connection con = createConnection();
            conList.add(con);
        }
    }
    
    public static Connection getConnection() {
        if(conList.isEmpty()==false) {
            Connection con = conList.get(0);
            conList.remove(con);
            return con;
        }else {
            return createConnection();
        }
    }
    
    
    private static Connection createConnection() {
        try {
            Class.forName("com.mysql.jdbc.Driver");
            
            return DriverManager.getConnection(connectionURL, username, password);
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        
        return null;
    }
    
    public static void close(ResultSet rs,Statement stmt,Connection con) {
        closeResultSet(rs);
        closeStatement(stmt);
        closeConnection(con);
    }
    public static void close(Statement stmt1,Statement stmt2,Connection con) {
        closeStatement(stmt1);
        closeStatement(stmt2);
        closeConnection(con);
    }
    
    
    private static void closeResultSet(ResultSet rs ) {
        try {
            if(rs!=null)rs.close();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    private static void closeStatement(Statement stmt) {
        try {
            if(stmt!=null)
                stmt.close();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    private static void closeConnection(Connection con) {
//        try {
//            if(con!=null)con.close();
//        } catch (SQLException e) {
//            // TODO Auto-generated catch block
//            e.printStackTrace();
//        }
        conList.add(con);
    }
}

    //由username1向username2转账金额
    public static void transferAccount(String username1,String username2,int money) throws SQLException {
        Connection con = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        try {
            con = JDBCUtils.getConnection();
            
            String sql = "update garytb set balance = balance - ? where username = ?";
            stmt = con.prepareStatement(sql);
            stmt.setInt(1, money);
            stmt.setString(2, username1);
            stmt.executeUpdate();// 返回值代表收到影响的行数
            
            sql = "update garytb set balance = balance + ? where username = ?";
            stmt = con.prepareStatement(sql);
            stmt.setInt(1, money);
            stmt.setString(2, username2);
            stmt.executeUpdate();// 返回值代表收到影响的行数
            System.out.println("操作成功！！");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.close(rs, stmt, con);
        }
    }

二、在扣款和收款操作之间添加一个隐式异常

　　当程序运行到异常代码块时，程序不会往下继续执行,因此a方1000元已扣除但b方未收到1000元款项

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 JDBC01 {

    public static void main(String[] args) throws SQLException  {
        transferAccount("a","b",1000);
    }

    public static void selectAll() throws SQLException {
        //注册驱动    使用驱动连接数据库
        Connection con = null;
        Statement stmt = null;
        ResultSet rs = null;
        try {
            //数据库的连接
            con = JDBCUtils.getConnection();
            
            //数据库的增删改查
            stmt = con.createStatement();
            //返回一个结果集
            rs =stmt.executeQuery("select * from garytb");
            
            while(rs.next()) {
                //System.out.println(rs.getString(1)+","+rs.getString(2)+","+rs.getString(3));
                System.out.println(rs.getString("id")+","+rs.getString("username")+","+rs.getString("password"));
            }
        
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally {
            JDBCUtils.close(rs, stmt, con);
        }
    }

    //校验用户
    public static boolean  selectByUernamePassword(String username,String password) throws SQLException {
        Connection con=null;
        Statement stmt = null;
        ResultSet rs = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            
            String url ="jdbc:mysql://localhost:3306/garysql?useUnicode=true&characterEncoding=UTF8&useSSL=false";
            con = DriverManager.getConnection(url,"root","123456");
            stmt =con.createStatement();
            String sql = "select * from garytb where username = '"+username+"' and password = '"+password+"'";
            //System.out.println(sql);
            rs = stmt.executeQuery(sql);
            
            if(rs.next()) {
                return true;
            }else {
                return false;
            }
                
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally {
            if(rs!=null)
                rs.close();
            if(stmt!=null)
                stmt.close();
            if(con!=null)
                con.close();
        }
        
        return false;
    }

    public static boolean selectByUP2(String username,String password) throws SQLException{
        Connection con=null;
        Statement stmt = null;
        ResultSet rs = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            
            String url ="jdbc:mysql://localhost:3306/garysql?useUnicode=true&characterEncoding=UTF8&useSSL=false";
            con = DriverManager.getConnection(url,"root","123456");
            
            String sql = "select * from garytb where username = ? and password = ?";
            PreparedStatement pstmt = con.prepareStatement(sql);
            //添加参数
            pstmt.setString(1, username);
            pstmt.setString(2, password);
            //进行查询
            rs = pstmt.executeQuery();
                
            if(rs.next()) {
                return true;
            }else {
                return false;
            }
                
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally {
            if(rs!=null)
                rs.close();
            if(stmt!=null)
                stmt.close();
            if(con!=null)
                con.close();
        }
        
        return false;
    }

    //pageNumber是页数，第几页，pageCount是每页显示多少个数据
    public static void selectUserByPage(int pageNumber,int pageCount) throws SQLException {
        //注册驱动    使用驱动连接数据库
                Connection con = null;
                PreparedStatement stmt = null;
                ResultSet rs = null;
                try {
                    Class.forName("com.mysql.jdbc.Driver");
                    
                    //String url ="jdbc:mysql://localhost:3306/garysql";
                    //指定编码查询数据库
                    String url ="jdbc:mysql://localhost:3306/garysql?useUnicode=true&characterEncoding=UTF8&useSSL=false";
                    String user = "root";
                    String password = "123456";
                    //建立和数据库的连接
                    con = DriverManager.getConnection(url,user,password);
                    
                    stmt = con.prepareStatement("select * from garytb limit ?,?");
                    stmt.setInt(1, (pageNumber-1)*pageCount );
                    stmt.setInt(2, pageCount);
                    
                    rs = stmt.executeQuery();
                    
                    while(rs.next()) {
                        //System.out.println(rs.getString(1)+","+rs.getString(2)+","+rs.getString(3));
                        System.out.println(rs.getString("id")+","+rs.getString("username")+","+rs.getString("password"));
                    }
                
                } catch (Exception e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }finally {
                    if(rs!=null)
                        rs.close();
                    if(stmt!=null)
                        stmt.close();
                    if(con!=null)
                        con.close();
                }
    }

    //crud: create read update delete
    //插入语句
    public static void insert(String username,String password) throws SQLException {
        //注册驱动    使用驱动连接数据库
        Connection con = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        try {
            con = JDBCUtils.getConnection();
            String sql = "insert into garytb(username,password) values(?,?)";
            stmt = con.prepareStatement(sql);
            stmt.setString(1, username);
            stmt.setString(2, password);
            int result =stmt.executeUpdate();// 返回值代表收到影响的行数
            System.out.println("插入成功"+username);
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally {
            JDBCUtils.close(rs, stmt, con);
        }
    }
    //删除语句
    public static void delete(int id) throws SQLException {
        //注册驱动    使用驱动连接数据库
        Connection con = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        try {
            con = JDBCUtils.getConnection();
            
            String sql = "delete from garytb where id = ?";
            stmt = con.prepareStatement(sql);
            stmt.setInt(1, id);
            int result =stmt.executeUpdate();// 返回值代表收到影响的行数
            if(result>0) {
                System.out.println("删除成功");
            }else {
                System.out.println("删除失败");
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.close(rs, stmt, con);
        }
    }
    //修改语句
    public static void update(int id,String newPassword) throws SQLException {
        Connection con = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        try {
            con = JDBCUtils.getConnection();
            
            String sql = "update garytb set password = ? where id = ?";
            stmt = con.prepareStatement(sql);
            stmt.setString(1, newPassword);
            stmt.setInt(2, id);
            int result =stmt.executeUpdate();// 返回值代表收到影响的行数
            if(result>0) {
                System.out.println("修改成功");
            }else {
                System.out.println("修改失败");
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.close(rs, stmt, con);
        }
    }

    //事物操作
    //由username1向username2转账金额
    public static void transferAccount(String username1,String username2,int money)  {
        Connection con = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        try {
            con = JDBCUtils.getConnection();
            
            String sql = "update garytb set balance = balance - ? where username = ?";
            stmt = con.prepareStatement(sql);
            stmt.setInt(1, money);
            stmt.setString(2, username1);
            stmt.executeUpdate();// 返回值代表收到影响的行数
            
            //显示异常throw new Exception("出现错误");
            //隐示异常 空指针异常
            String s = null;
            s.charAt(2);
            
            sql = "update garytb set balance = balance + ? where username = ?";
            stmt = con.prepareStatement(sql);
            stmt.setInt(1, money);
            stmt.setString(2, username2);
            stmt.executeUpdate();// 返回值代表收到影响的行数
            System.out.println("操作成功！！");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.close(rs, stmt, con);
        }
    }
    
}

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;

public class JDBCUtils {
    
    private static final String connectionURL = "jdbc:mysql://localhost:3306/garysql?useUnicode=true&characterEncoding=UTF8&useSSL=false";
    private static final String username = "root";
    private static final String password = "123";
    
    private static ArrayList<Connection> conList = new ArrayList<Connection>();
    
    static {
        for(int i =0;i<5;i++) {
            Connection con = createConnection();
            conList.add(con);
        }
    }
    
    public static Connection getConnection() {
        if(conList.isEmpty()==false) {
            Connection con = conList.get(0);
            conList.remove(con);
            return con;
        }else {
            return createConnection();
        }
    }
    
    
    private static Connection createConnection() {
        try {
            Class.forName("com.mysql.jdbc.Driver");
            
            return DriverManager.getConnection(connectionURL, username, password);
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        
        return null;
    }
    
    public static void close(ResultSet rs,Statement stmt,Connection con) {
        closeResultSet(rs);
        closeStatement(stmt);
        closeConnection(con);
    }
    public static void close(Statement stmt1,Statement stmt2,Connection con) {
        closeStatement(stmt1);
        closeStatement(stmt2);
        closeConnection(con);
    }
    
    
    private static void closeResultSet(ResultSet rs ) {
        try {
            if(rs!=null)rs.close();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    private static void closeStatement(Statement stmt) {
        try {
            if(stmt!=null)
                stmt.close();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    private static void closeConnection(Connection con) {
//        try {
//            if(con!=null)con.close();
//        } catch (SQLException e) {
//            // TODO Auto-generated catch block
//            e.printStackTrace();
//        }
        conList.add(con);
    }
}

    //由username1向username2转账金额
    public static void transferAccount(String username1,String username2,int money)  {
        Connection con = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        try {
            con = JDBCUtils.getConnection();
            
            String sql = "update garytb set balance = balance - ? where username = ?";
            stmt = con.prepareStatement(sql);
            stmt.setInt(1, money);
            stmt.setString(2, username1);
            stmt.executeUpdate();// 返回值代表收到影响的行数
            
            //显示异常throw new Exception("出现错误");
            //隐示异常 空指针异常
            String s = null;
            s.charAt(2);
            
            sql = "update garytb set balance = balance + ? where username = ?";
            stmt = con.prepareStatement(sql);
            stmt.setInt(1, money);
            stmt.setString(2, username2);
            stmt.executeUpdate();// 返回值代表收到影响的行数
            System.out.println("操作成功！！");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.close(rs, stmt, con);
        }
    }

三、添加事物　　

　　一旦事物之间出现异常，则不会提交事物给数据库

　　//开启事物 是否自动提交
　　con.setAutoCommit(false);

　　//当事物中所有事物都完成了才会提交
　　con.commit();

　　当a向b转账1000元后出现异常，b未收到1000元，这一系列操作处于同一事物中，此事物有异常不会提交给程序

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 JDBC01 {

    public static void main(String[] args) throws SQLException  {
        transferAccount("a","b",1000);
    }

    public static void selectAll() throws SQLException {
        //注册驱动    使用驱动连接数据库
        Connection con = null;
        Statement stmt = null;
        ResultSet rs = null;
        try {
            //数据库的连接
            con = JDBCUtils.getConnection();
            
            //数据库的增删改查
            stmt = con.createStatement();
            //返回一个结果集
            rs =stmt.executeQuery("select * from garytb");
            
            while(rs.next()) {
                //System.out.println(rs.getString(1)+","+rs.getString(2)+","+rs.getString(3));
                System.out.println(rs.getString("id")+","+rs.getString("username")+","+rs.getString("password"));
            }
        
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally {
            JDBCUtils.close(rs, stmt, con);
        }
    }

    //校验用户
    public static boolean  selectByUernamePassword(String username,String password) throws SQLException {
        Connection con=null;
        Statement stmt = null;
        ResultSet rs = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            
            String url ="jdbc:mysql://localhost:3306/garysql?useUnicode=true&characterEncoding=UTF8&useSSL=false";
            con = DriverManager.getConnection(url,"root","123456");
            stmt =con.createStatement();
            String sql = "select * from garytb where username = '"+username+"' and password = '"+password+"'";
            //System.out.println(sql);
            rs = stmt.executeQuery(sql);
            
            if(rs.next()) {
                return true;
            }else {
                return false;
            }
                
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally {
            if(rs!=null)
                rs.close();
            if(stmt!=null)
                stmt.close();
            if(con!=null)
                con.close();
        }
        
        return false;
    }

    public static boolean selectByUP2(String username,String password) throws SQLException{
        Connection con=null;
        Statement stmt = null;
        ResultSet rs = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            
            String url ="jdbc:mysql://localhost:3306/garysql?useUnicode=true&characterEncoding=UTF8&useSSL=false";
            con = DriverManager.getConnection(url,"root","123456");
            
            String sql = "select * from garytb where username = ? and password = ?";
            PreparedStatement pstmt = con.prepareStatement(sql);
            //添加参数
            pstmt.setString(1, username);
            pstmt.setString(2, password);
            //进行查询
            rs = pstmt.executeQuery();
                
            if(rs.next()) {
                return true;
            }else {
                return false;
            }
                
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally {
            if(rs!=null)
                rs.close();
            if(stmt!=null)
                stmt.close();
            if(con!=null)
                con.close();
        }
        
        return false;
    }

    //pageNumber是页数，第几页，pageCount是每页显示多少个数据
    public static void selectUserByPage(int pageNumber,int pageCount) throws SQLException {
        //注册驱动    使用驱动连接数据库
                Connection con = null;
                PreparedStatement stmt = null;
                ResultSet rs = null;
                try {
                    Class.forName("com.mysql.jdbc.Driver");
                    
                    //String url ="jdbc:mysql://localhost:3306/garysql";
                    //指定编码查询数据库
                    String url ="jdbc:mysql://localhost:3306/garysql?useUnicode=true&characterEncoding=UTF8&useSSL=false";
                    String user = "root";
                    String password = "123456";
                    //建立和数据库的连接
                    con = DriverManager.getConnection(url,user,password);
                    
                    stmt = con.prepareStatement("select * from garytb limit ?,?");
                    stmt.setInt(1, (pageNumber-1)*pageCount );
                    stmt.setInt(2, pageCount);
                    
                    rs = stmt.executeQuery();
                    
                    while(rs.next()) {
                        //System.out.println(rs.getString(1)+","+rs.getString(2)+","+rs.getString(3));
                        System.out.println(rs.getString("id")+","+rs.getString("username")+","+rs.getString("password"));
                    }
                
                } catch (Exception e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }finally {
                    if(rs!=null)
                        rs.close();
                    if(stmt!=null)
                        stmt.close();
                    if(con!=null)
                        con.close();
                }
    }

    //crud: create read update delete
    //插入语句
    public static void insert(String username,String password) throws SQLException {
        //注册驱动    使用驱动连接数据库
        Connection con = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        try {
            con = JDBCUtils.getConnection();
            String sql = "insert into garytb(username,password) values(?,?)";
            stmt = con.prepareStatement(sql);
            stmt.setString(1, username);
            stmt.setString(2, password);
            int result =stmt.executeUpdate();// 返回值代表收到影响的行数
            System.out.println("插入成功"+username);
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally {
            JDBCUtils.close(rs, stmt, con);
        }
    }
    //删除语句
    public static void delete(int id) throws SQLException {
        //注册驱动    使用驱动连接数据库
        Connection con = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        try {
            con = JDBCUtils.getConnection();
            
            String sql = "delete from garytb where id = ?";
            stmt = con.prepareStatement(sql);
            stmt.setInt(1, id);
            int result =stmt.executeUpdate();// 返回值代表收到影响的行数
            if(result>0) {
                System.out.println("删除成功");
            }else {
                System.out.println("删除失败");
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.close(rs, stmt, con);
        }
    }
    //修改语句
    public static void update(int id,String newPassword) throws SQLException {
        Connection con = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        try {
            con = JDBCUtils.getConnection();
            
            String sql = "update garytb set password = ? where id = ?";
            stmt = con.prepareStatement(sql);
            stmt.setString(1, newPassword);
            stmt.setInt(2, id);
            int result =stmt.executeUpdate();// 返回值代表收到影响的行数
            if(result>0) {
                System.out.println("修改成功");
            }else {
                System.out.println("修改失败");
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.close(rs, stmt, con);
        }
    }

    //事物操作
    //由username1向username2转账金额
    public static void transferAccount(String username1,String username2,int money)  {
        Connection con = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        try {
            con = JDBCUtils.getConnection();
            
            //开启事物 是否自动提交
            con.setAutoCommit(false);
            
            String sql = "update garytb set balance = balance - ? where username = ?";
            stmt = con.prepareStatement(sql);
            stmt.setInt(1, money);
            stmt.setString(2, username1);
            stmt.executeUpdate();// 返回值代表收到影响的行数
            
            //显示异常throw new Exception("出现错误");
            //隐示异常 空指针异常
            
            
            sql = "update garytb set balance = balance + ? where username = ?";
            stmt = con.prepareStatement(sql);
            stmt.setInt(1, money);
            stmt.setString(2, username2);
            stmt.executeUpdate();// 返回值代表收到影响的行数
            System.out.println("操作成功！！");
            
            //提交事务
            //当事物中所有事物都完成了才会提交
            con.commit();
            
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.close(rs, stmt, con);
        }
    }
    
}

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;

public class JDBCUtils {
    
    private static final String connectionURL = "jdbc:mysql://localhost:3306/garysql?useUnicode=true&characterEncoding=UTF8&useSSL=false";
    private static final String username = "root";
    private static final String password = "123";
    
    private static ArrayList<Connection> conList = new ArrayList<Connection>();
    
    static {
        for(int i =0;i<5;i++) {
            Connection con = createConnection();
            conList.add(con);
        }
    }
    
    public static Connection getConnection() {
        if(conList.isEmpty()==false) {
            Connection con = conList.get(0);
            conList.remove(con);
            return con;
        }else {
            return createConnection();
        }
    }
    
    
    private static Connection createConnection() {
        try {
            Class.forName("com.mysql.jdbc.Driver");
            
            return DriverManager.getConnection(connectionURL, username, password);
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        
        return null;
    }
    
    public static void close(ResultSet rs,Statement stmt,Connection con) {
        closeResultSet(rs);
        closeStatement(stmt);
        closeConnection(con);
    }
    public static void close(Statement stmt1,Statement stmt2,Connection con) {
        closeStatement(stmt1);
        closeStatement(stmt2);
        closeConnection(con);
    }
    
    
    private static void closeResultSet(ResultSet rs ) {
        try {
            if(rs!=null)rs.close();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    private static void closeStatement(Statement stmt) {
        try {
            if(stmt!=null)
                stmt.close();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    private static void closeConnection(Connection con) {
//        try {
//            if(con!=null)con.close();
//        } catch (SQLException e) {
//            // TODO Auto-generated catch block
//            e.printStackTrace();
//        }
        conList.add(con);
    }
}

    

//事物操作
    //由username1向username2转账金额
    public static void transferAccount(String username1,String username2,int money)  {
        Connection con = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        try {
            con = JDBCUtils.getConnection();
            
            //开启事物 是否自动提交
            con.setAutoCommit(false);
            
            String sql = "update garytb set balance = balance - ? where username = ?";
            stmt = con.prepareStatement(sql);
            stmt.setInt(1, money);
            stmt.setString(2, username1);
            stmt.executeUpdate();// 返回值代表收到影响的行数
            
            //显示异常throw new Exception("出现错误");
            //隐示异常 空指针异常
            
            
            sql = "update garytb set balance = balance + ? where username = ?";
            stmt = con.prepareStatement(sql);
            stmt.setInt(1, money);
            stmt.setString(2, username2);
            stmt.executeUpdate();// 返回值代表收到影响的行数
            System.out.println("操作成功！！");
            
            //提交事务
            //当事物中所有事物都完成了才会提交
            con.commit();
            
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.close(rs, stmt, con);
        }
    }