增加异常捕获，当作业未找到相应文件时，跳到文件未找到页面(不报500错误)

app/controllers/zipdown_controller.rb

@@ -41,7 +41,7 @@ class ZipdownController < ApplicationController
       if homework != nil
         if homework.attachments.count > 0
           zipfile = zip_homework_by_user homework
-          send_file zipfile, :filename => homework.name+".zip", :type => detect_content_type(zipfile) if zipfile
+          send_file zipfile, :filename => homework.name+".zip", :type => detect_content_type(zipfile) if(zipfile)
         else
           render_403 :message => :no_file_dowmload
         end
@@ -51,6 +51,8 @@ class ZipdownController < ApplicationController
     else
       render_403 :message => :notice_not_authorized
     end
+  rescue => e
+    render file: 'public/file_not_found.html'
   end
 
   private