文件下載時文件不存在的返回值

				//轉碼
                response.setContentType("text/html; charset=UTF-8");
                PrintWriter out = null;
                try {
                    out = response.getWriter();
                } catch (IOException e) {
                    e.printStackTrace();
                }
                out.flush();
                out.println("{\n" +
                        "    \"code\": 300,\n" +
                        "    \"msg\": \"文件不存在或已經被刪除\"\n" +
                        "}");
                out.close();