如果在数据库中找不到用户数据，如何中断while循环

Question

I'm trying to make a application in which put some data in database and from the html page i want to search the data in database. I'm using the servlet api, i successfully retrieve the data from the database, but for the data which is not present in the database i required to get the "data not found" message on the same html page. I write the condition for checking the data for database, but for the data not present in the database i get the error message of "null pointer exception" and the while loop doesn't break by itself after checking whole data in database.

// this while loop doesn't terminate by itself if the data is not found in the database.

int flag=0;
while(rs.next()){
    if (rs.getString(1).equals(fname)&&(rs.getString(2).equals(lname)))
    {
        String message=rs.getString(4);
        out.print("<h2 align='center'>"+message+"</h2>");
        RequestDispatcher disp = req.getRequestDispatcher("/index.html");
        disp.include(req,res);
        flag=1;
    }
}

if(flag==0)
{
    out.print("<h1>"+"data not found"+"</h1>");
    RequestDispatcher disp = req.getRequestDispatcher("/index.html");
    disp.include(req,res);
    System.out.println(flag);        
}
}

Answer 1

You should assign the value to a variable then check if is not null first:

String tmp = rs.getString(1);
        if (tmp != null && tmp.equals(fname) && tmp.equals(lname)) {...}