单个表的查询，通用查询

先上最容易懂的表

@Test
    public void testQuery1() {
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet resultSet = null;
        try {
            conn = JDBCUtils.getConnection();
            String sql = "select id,name,email,birth from customers where id = ?";
            ps = conn.prepareStatement(sql);
            ps.setObject(1, 1);
            
            //执行,并返回结果集
            resultSet = ps.executeQuery();
            //处理结果集
            if(resultSet.next()){//next():判断结果集的下一条是否有数据，如果有数据返回true,并指针下移；如果返回false,指针不会下移。
                
                //获取当前这条数据的各个字段值
                int id = resultSet.getInt(1);
                String name = resultSet.getString(2);
                String email = resultSet.getString(3);
                Date birth = resultSet.getDate(4);
                
            //方式一：
//            System.out.println("id = " + id + ",name = " + name + ",email = " + email + ",birth = " + birth);
                
            //方式二：
//            Object[] data = new Object[]{id,name,email,birth};
                //方式三：将数据封装为一个对象（推荐）
                Customer customer = new Customer(id, name, email, birth);
                System.out.println(customer);
                
            }
        } catch (Exception e) {
            e.printStackTrace();
        }finally{
            //关闭资源
            JDBCUtils.closeResource(conn, ps, resultSet);
            
        }

这个方法把sql语句写在里面而且一些变量也写了进去

所以我们首先先把变量写进一个类里面去，然后直接调用这个类就可以达到这个效果

然后再把语句搞出来

    @Test
    public void testQueryForCustomers(){
        String sql = "select id,name,birth,email from customers where id = ?";
        Customer customer = queryForCustomers(sql, 13);
        System.out.println(customer);
        
        sql = "select name,email from customers where name = ?";
        Customer customer1 = queryForCustomers(sql,"周杰伦");
        System.out.println(customer1);
    }
    
    /**
     * 
     * @Description 针对于customers表的通用的查询操作
     * @author shkstart
     * @throws Exception 
     * @date 上午10:23:40
     */
    public Customer queryForCustomers(String sql,Object...args){
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        try {
            conn = JDBCUtils.getConnection();
            
            ps = conn.prepareStatement(sql);
            for(int i = 0;i < args.length;i++){
                ps.setObject(i + 1, args[i]);
            }
            
            rs = ps.executeQuery();
            //获取结果集的元数据 :ResultSetMetaData
            ResultSetMetaData rsmd = rs.getMetaData();
            //通过ResultSetMetaData获取结果集中的列数
            int columnCount = rsmd.getColumnCount();
            
            if(rs.next()){
                Customer cust = new Customer();
                //处理结果集一行数据中的每一个列
                for(int i = 0;i <columnCount;i++){
                    //获取列值
                    Object columValue = rs.getObject(i + 1);
                    
                    //获取每个列的列名
//                    String columnName = rsmd.getColumnName(i + 1);
                    String columnLabel = rsmd.getColumnLabel(i + 1);
                    
                    //给cust对象指定的columnName属性，赋值为columValue：通过反射
                    Field field = Customer.class.getDeclaredField(columnLabel);
                    field.setAccessible(true);
                    field.set(cust, columValue);
                }
                return cust;
            }
        } catch (Exception e) {
            e.printStackTrace();
        }finally{
            JDBCUtils.closeResource(conn, ps, rs);
            
        }
        
        return null;
        
        
    }