用action直接输出public ActionForward execute(ActionMapping mapping, ActionForm form,
HttpServletRequest request, HttpServletResponse response) {
OutputStream out = null;
try {
                        byte[] pic = ...//得到图片
response.setContentType("image/jpg");//如果是jpg的图片   
out=response.getOutputStream();
out.write(pic); 
out.flush(); 
} catch (Exception e) {
} finally{
try {
if(out!=null)out.close();
} catch (IOException e) {
e.printStackTrace();
}
}
return null;
}