读取blob字段，生成文件不成功！！！！！！！！！！

程序如下：
有没有高人给看看?

String targetfilename = "d:/target1.bmp";
FileOutputStream OutStream = new FileOutputStream(targetfilename);
String SQL = "select a,b from test";
Statement stmt = conn.createStatement();
ResultSet rs;
rs = stmt.executeQuery(SQL);
rs.next();
out.print("<br>id is "+rs.getString(1));
InputStream ss=null;
ss = rs.getBinaryStream(2);
out.print( "<br>Stream num:");
try{
int num;
byte[] buff = new byte[4*1024];
while((num=ss.read(buff,0,1024))!=-1){
OutStream.write(buff,0,num);
}
}catch(Exception e){
out.println("失败！！");
out.println("<BR>");
out.println(e);
OutStream.close();
}