java servlet中执行linux命令

public HttpServletResponse execCmd(String cmd, HttpServletRequest request, HttpServletResponse response) throws IOException {

          StringBuffer output = new StringBuffer();

          Process p = null;

          try {

               p = Runtime.getRuntime().exec(cmd);

               p.waitFor();

               BufferedReader  reader =new BufferedReader(new InputStreamReader(p.getInputStream()));

               String line = "";

               while( (line = reader.readLine()) != null) {

                    output.append(line + "\n");

               }

          } catch (Exception e) {

               e.printStackTrace();

          }

          PrintWriter pw = response.getWriter();

          pw.write(output.toString());

          return response;

     }