About ResultSet problem!

[Robert James]

Turnpage JavaBean file is here ..

package user;
import java.sql.*;
public class TurnPage
{
  Connection conn;
  Statement sql;
  ResultSet rs;
  String course,school,studydate,rule;
  int cpage,pages,pagesize,totals;
  public void setCourse(String course)
  {
    this.course=course;
  }
  public void setSchool(String school)
  {
    this.school=school;
  }
  public void setStudydate(String studydate)
  {
    this.studydate=studydate;
  }
  public void setRule(String rule)
  {
    this.rule=rule;
  }
  public int getPages()
  {
    return pages;
  }
  public int getTotals()
  {
    return totals;
  }
  public TurnPage()
  {
    pagesize=10;
    cpage=1;
    try
    {
      Class.forName("com.microsoft.jdbc.sqlserver.SQLServerDriver");
    }
    catch(ClassNotFoundException e)
    {
    }
    try
    {
      conn=DriverManager.getConnection("jdbc:microsoft:sqlserver://localhost:1433;DatabaseName=students","sa","");
      sql=conn.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,ResultSet.CONCUR_UPDATABLE);
      rs=sql.executeQuery("select count(*) as num from open");
      rs.next();
      totals=rs.getInt("num");
      rs.close();
      if(totals%pagesize>0)
      {
        pages=totals/pagesize+1;
      }
      else
      {
        pages=totals/pagesize;
      }
    }
    catch(SQLException e)
    {
    }
  }
public void insertRecord()
{
  try
  {
  String s="insert into open(course,school,studydate,rule)values('"+course+"','"+school+"','"+studydate+"','"+rule+"')";
  sql.executeUpdate(s);
}
catch(SQLException e)
{
}
}
public void updateRecord(String s)
{
  try
  {
    sql.executeUpdate(s);
  }
  catch(SQLException e)
  {
  }
}
 
public void closeData()
{
  try
  {
  if(rs!=null) rs.close();
  if(conn!=null) conn.close();
}
catch(SQLException e)
{
}
}
public ResultSet openData(int p) //
{
  try
  {
    
    cpage=p;
    rs=sql.executeQuery("select * from open");
    rs.absolute((cpage-1)*pagesize+1);
    return rs;
  }
  catch(SQLException e)
  {
    return null;
  }
}
    
    
}
 
  

Test.jsp is here ...

 <%@page contentType="text/html;charset=gb2312"%>
<%@page import="java.sql.*,user.*"%>
<jsp:useBean id="mydata" class="user.TurnPage" scope="page" />
<%
ResultSet rs;
int pages=mydata.getPages(); // return pages
int total=mydata.getTotals(); //return total records
out.println("Pages:"+pages);
out.println("Totals:"+total);
rs=mydata.openData(1); //turn to page one
if(rs==null)
{
out.print("error");
}
%>
 
 

Test.jsp Execute result is

Pages:4
Total:32
error

Would you like to tell me why the ResultSet rs didn't return .
Thanks a lot.
[ May 06, 2005: Message edited by: Bear Bibeault ]

[Bear Bibeault]

 catch(SQLException e)
  {
    return null;
  } 

Do you really think that this is a good way to deal with exceptions?

What's likely happening is that your code is throwing an exception and it is getting "eaten" by your catch block. Never, ever do this!

Either catch the exception and deal with it properly, or let it propogate outward so that the container can deal with it. By "eating" the exception as you have done here, you end up with head-scratching problems such as this.

[Robert James]

I'am Beginner. I don't know how to deal with this exception. in your opinion how you will do..

please help me change my code , make it work . thanks a lot. i hope the code ResultSet doesn't return null .

[Ben Souther]

At a bare minimum, log it:

   catch(SQLException e){
    e.printStackTrace();
   } 

This way you can go back to your log files and see what the problem was.

Further than that, ask yourself. What do I want to do if the code in this block fails -- redirect to an error page, continue showing an empty table?

[Bear Bibeault]

Since such an exception almost always means that either there's a bug in your code, or that the database itself is hosed, I let such exceptions propogate out to the container where the error handling mechansim that can be set up in web.xml causes a user-friendly "Oops!" page to be presented while logging the details of the error for me to diagnose.
[ May 07, 2005: Message edited by: Bear Bibeault ]