尚硅谷之JDBC

         /**

          * 执行查询操作的SQL语句，SQL可以带参数(?)

          * @param clazz Class 查询的结果需要封装的实体的Class类型，例如：学生Student，商品Goods,订单Order

          * @param sql String 执行查询操作的SQL语句

          * @param args Object... 对应的每个?设置的值，顺序要与?对应

          * @return T 封装了查询结果的实体

          * @throws Exception

          */

         public static <T> T get(Class<T> clazz,String sql,Object... args)throws Exception{

                   Connection conn = null;

                   PreparedStatement pst = null;

                   ResultSet rs = null;

                   T entity = null;

                   //1、获取连接

                   conn = JDBCUtils.getConnection();

                   //2、获取PreparedStatement对象，并预编译带参数?的SQL

                   pst = conn.prepareStatement(sql);

                   //3、设置参数?的值

                   if(args!=null && args.length>0){

                            for(int i=0;i<args.length;i++){

                                     pst.setObject(i+1, args[i]);

                            }

                   }

                   //4、执行SQL

                   rs = pst.executeQuery();

                   //5、获取结果，封装到对象中

                   if(rs.next()){

                            entity = clazz.newInstance();

                            /*

                             * 需要解决的问题？

                             * (1)查询了哪些列，即需要为哪些属性赋值，这些列对应的属性名是什么

                             * (2)获取这些列的值，用反射为属性赋值

                             *

                             * clazz：只能得到所有属性，不知道sql中查询了哪些列

                             * 只能依赖sql

                             */

                   }

                   JDBCUtils.free(rs, pst, conn);

                   return entity;

         }