无法在Servlet中设置ResultSet的属性

Question

In my project,I am getting the query result from the database into my servlet and passing the result to JSP after setting the attribute for the ResultSet and then accessing it in JSP.But somehow i am able to set and access my all other attributes in JSP and servlets except the ResultSet.

So here is my database access function getcart()

public static ResultSet getCart(int item,int cust){
ResultSet rs=null,res=null;
String i_name;
int price;
try{
    rs=stmnt.executeQuery("SELECT i_name,price FROM items WHERE i_id="+item);
    rs.next();
    i_name=rs.getString(1);
    price=rs.getInt(2);
    stmnt.executeUpdate("INSERT INTO cart(prod,price,c_id,i_id) VALUES('"+i_name+"',"+price+","+cust+","+item+")");
    res=stmnt.executeQuery("SELECT prod,price,count(*) FROM cart WHERE c_id="+cust+" GROUP BY i_id"); 
    res.next();
}catch(SQLException e){}
return res;

}

Here is the JSP

<%ResultSet r=(ResultSet)request.getAttribute("cart");%>
<div id="pageContent">
        <div style="margin:24px; text-align:left;"><br />
        <table width="100%" border="2" cellspacing="0" id ="table1">
            <tr>
            <td width="15%" bgcolor="#000000" align="center"><strong>Product</strong></td>
            <td width="10%" bgcolor="#000000" align="center"><strong>Price</strong></td>
            <td width="12%" bgcolor="#000000" align="center"><strong>Quantity</strong></td>
            <!--<td width="9%" bgcolor="#000000" align="center"><strong>Total</strong></td>-->
            </tr>
            <%while(r.next()){%>
            <tr class="spaceUnder">
                <td width="15%" bgcolor="#FFFFFF" align="center"><font color="#000"> <%=re.getString(1)%></font></td>
                    <td width="10%" bgcolor="#FFFFFF" align="center"><font color="#000"> <%=re.getInt(2)%></font></td>
            <td width="12%" bgcolor="#FFFFFF" align="center"><font color="#000"> <%=re.getInt(3)%> </font></td>
            </tr>
            <%}%>
        </table> 
            <div class="container">
        <left><h3 style="color:#FFFFF;padding-top:30px;"><font color="#000">Total: <%=total%> </font></h3></left>
            </div>
        </div>
</div>

And here is the servlets snippet:

                res=accessDB.getCart(it,ci);
                request.setAttribute("cart",res);
                view=request.getRequestDispatcher("cart.jsp");
                view.forward(request, response);         

I dont know WHAT is happening?? I have now spent a lot of time on this.And my database is not empty.So res.next() is valid.

One thing is working.When i break down my ResultSet in my servlets code using getInt and getString ,and then send these to JSP individually instead of sending the whole ResultSet ,then getAttribute in JSP works and i can print my result.But don't know why the whole ResultSet is not going.I am using Netbeans 8.0.1.

Please Help.

Answer 1

From my observation, I think your Query SELECT prod,price,count(*) FROM cart WHERE c_id="+cust+" GROUP BY i_id returns only one row.

First of all you should not use res.next(); just before returning RESULTSET object. This is a wrong way of designing a function. What getCart(int item,int cust) should do is just return the RESULTSET .

Problem that I assume , that seems to be here is that, your query just returns one row. As you call res.next(); just before returning the RESULTSET object. The resultset cursor already points to the first row of the result.

When you call <%while(r.next()){%> , this time it gets NULL , because next row in resultset is non-existent. That`s why result cannot be printed.

---

What I have observed now that you have made a typo in you jsp code. <%=re.getString(1)%> what it should be is <%=r.getString(1)%> beacause you are creating <%ResultSet r=(ResultSet)request.getAttribute("cart");%> Resultset variable named r but you are using re . But re does not exist in the file. I think JSP should not even compile, because re variable is never defined.

That s the reason it s not working.