while(rs.next()){
String filename=rs.getString("filename");
String url="E:/StuFiles/" + filename;
File f=new File(url);
rs.close();
flag=f.delete();
}你已经把rs给close了,怎么可能循环得下去啊???改成 :   while(rs.next()){
String filename=rs.getString("filename");
String url="E:/StuFiles/" + filename;
File f=new File(url);
flag=f.delete();
}
rs.close();
                  stmt.close();
                  coon.close();