对创建连接、查询、增删改 的简单封装，在数据库事务案例中，该类不是关键，只是为了方便验证例子，做的简单封装

package test;

import java.sql.*;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class Db {

    public static Connection connect(String driver,String url,String username,String password) throws ClassNotFoundException, SQLException {
        Class.forName(driver);
        Connection connection = DriverManager.getConnection(url, username, password);

        return connection;
    }

    public static int update(Connection connection,String sql) throws SQLException {
        PreparedStatement ps = null;
        try {
            ps= connection.prepareStatement(sql);
            int i = ps.executeUpdate();
            return i;
        }finally {
            if(ps!=null) {
                ps.close();
            }
        }
    }

    public static List<Map> query(Connection connection, String sql) throws SQLException{
        PreparedStatement pstm = null;
        ResultSet rs = null;
        List<Map> retList = new ArrayList();
        try {
            pstm = connection.prepareStatement(sql);
            rs = pstm.executeQuery();

            ResultSetMetaData rsmd=rs.getMetaData();
            //查询的列数
            int count=rsmd.getColumnCount();
            while(rs.next()){
                Map record=new HashMap();
                for(int i=0   ; i<count   ; i++  ){
                    record.put(rsmd.getColumnLabel(i+1), rs.getObject(i+1));
                }
                //将数组放入到List中
                retList.add(record);
            }
        }finally {
            //查询后要释放资源
            if(rs!=null) {
                try {
                    rs.close();
                } catch (SQLException e) {
                }
            }
            if(pstm!=null) {
                try {
                    pstm.close();
                } catch (SQLException e) {
                }
            }
        }
        return retList;
    }
}

原文出处：/show_1IX78ERNaC5p.html