2020/11/3

一.对信息登录进行判断，判断信息是不是在数据库当中

public student searchID(String x){//查询
	    String sql="select * from text3 where sid='"+x+"'";
	    Connection conn=DBUtil.getConn();
	    Statement st=null;
	    List<student> list=new ArrayList<>();
	    ResultSet rs=null;
	    student bean=null;
	    try {
	    		st=conn.createStatement();
	   
	    		rs=st.executeQuery(sql);
	    		rs.next();
	    		String sid = rs.getString("sid");
                String sname = rs.getString("sname");
                String ssex = rs.getString("ssex");
                String sclass=rs.getString("sclass");
                String szy = rs.getString("szy");

	            bean=new student(sid,sname,ssex,sclass,szy);
	    } catch (SQLException e) {
	        // TODO Auto-generated catch block
	        e.printStackTrace();
	    }
	    finally {
	        DBUtil.close(rs, st, conn);
	    }
	    return bean;
	}
	
	
	public boolean judge(String m)
	{
		if(searchID(m)==null)
		{
			return false;
		}
		else
			return true;
			
	}

 在这里使用了一个查询的函数，另外在dao中又使用了一个judge函数，在这个函数当中，调用查询的函数，对查询的东西进行判断，返回值不为空，那么有

二.

public List<student> scha (String n,String m) {
			String sql="select * from text3 where ";
			if(m!="") {
					sql+=""+n+" = '"+m+"'";		
			}
			Connection conn = DBUtil.getConn();
			Statement state = null;
			System.out.println(sql);
			ResultSet rs = null;
			List<student> list = new ArrayList<>();
			try {
				state = conn.createStatement();
				rs = state.executeQuery(sql);
				student bean = null;
				while (rs.next()) {
					String sid = rs.getString("sid");
	                String sname = rs.getString("sname");
	                String ssex = rs.getString("ssex");
	                String sclass=rs.getString("sclass");
	                String szy = rs.getString("szy");

		            bean=new student(sid,sname,ssex,sclass,szy);
					list.add(bean);
				}
			} catch (Exception e) {
				e.printStackTrace();
			} finally {
				DBUtil.close(state, conn);
			}
			return list;
		}

 在使用这个的时候应该如何判断

三.session