学生管理系统之查询实现

1.dao层实现

• 接口

public interface StudentDaoInte {
 
    List<Student> selectCondition(Map<String, String> whereMap);
}

• 实现

@Override
    //条件查询
    public List<Student> selectCondition(Map<String, String> whereMap) {

        //用来 存储 合法 的 参数的值
        List<String> list = new ArrayList<>();

        //用来  拼接sql 语句的where条件
        StringBuilder where = new StringBuilder();

        //遍历迭代 whereMap
        Set<String> keySet =  whereMap.keySet();
        Iterator<String> its = keySet.iterator();

        while(its.hasNext()){
           String key =  its.next();//键:字段
           String val = whereMap.get(key);//值: 字段值
            //判断是否为空,空字符串和 0
           if(val != null && !"".equals(val.trim()) && !"0".equals(val.trim())){

               //对 name  进行模糊查询
               if("name".equals(key)){
                   where.append(" and "+key+" like ?");
                   list.add("%"+val+"%");
               }else{
                   //拼接条件
                   where.append(" and "+key+"=?");
                   list.add(val);
               }
           }
        }

        //为了  让 拼接 sql 从and 开始，加 1=1 恒成立条件
        String sql = "select * from students where 1=1"+where;

        BeanListHandler<Student> handler = new BeanListHandler<Student>(Student.class);

        //将 list 合法参数 转换 成 对象数组
        Object[] args = list.toArray();

        return DBUtil.select(sql,handler,args);
    }

2.entity层实现

3.service层实现

• 接口

//    按条件查询
    List<Student> queryCondition(Map<String, String> whereMap);

• 实现

  @Override
    public List<Student> queryCondition(Map<String, String> whereMap) {

        return sdi.selectCondition(whereMap);
    }

4.servlet层实现

 case "search":

                String sno = req.getParameter("sno");
                String name = req.getParameter("name");
                String class_id = req.getParameter("class_id");

                Map<String ,String> whereMap = new HashMap<>();
                whereMap.put("id",sno);
                whereMap.put("name",name);
                whereMap.put("class_id",class_id);

                List<Student> list = ssi.queryCondition(whereMap);
                req.setAttribute("list",list);

                List<Classes> clz_list = csi.queryAll();
                req.setAttribute("clz_list",clz_list);

                req.setAttribute("where",whereMap);

                req.getRequestDispatcher("/WEB-INF/sms/stu/list.jsp").forward(req,resp);

                break;
            default:break;
        }
        
   private Map<String, String> getParameterMap(HttpServletRequest req) {
        DiskFileItemFactory diskFileItemFactory = new DiskFileItemFactory();
        FileUpload fileUpload = new FileUpload(diskFileItemFactory);

        Map<String,String> map = new HashMap<>();
        try {
            List<FileItem> list = fileUpload.parseRequest(req);

            for (FileItem fileItem : list) {

                if(fileItem.isFormField()){//判断是否是 普通的表单项

                    map.put(fileItem.getFieldName(),new String(fileItem.getString().getBytes("ISO8859-1"),"utf-8"));
                    map.put(fileItem.getFieldName(),fileItem.getString());

                }else{//说明是 文件上传的表单项,处理 上传文件,将上传文件 保存到服务器的硬盘中

                    //拼接路径
                    String path = this.getServletContext().getRealPath("/")+"upload"+ File.separator;
                    String fileName = UUID.randomUUID().toString();
                    String suffix = fileItem.getName().substring(fileItem.getName().lastIndexOf('.'));

                    //TODO 验证 大小、类型 等是否符合要求

//                            System.out.println(path+fileName+suffix);
                    File file = new File(path+fileName+suffix);
                    fileItem.write(file);

                    //将 路径 存储到 map ,以再便存到数据库里
                    map.put(fileItem.getFieldName(),"/upload/"+fileName+suffix);
                }
            }

        } catch (FileUploadException e) {
            e.printStackTrace();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return map;
    }

5.utils层实现

 public static <T> List<T>  select(String sql, BeanListHandler<T> beanListHandler, Object... args){
        List<T> list = null;
        try {
            list =  runner.query(sql,beanListHandler,args);
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return list;
    }

6.效果图