正则表达式验证URL

var str ="^(http|https|ftp)\\://([a-zA-Z0-9\\.\\-]+(\\:[a-zA-"
   + "Z0-9\\.&%\\$\\-]+)*@)?((25[0-5]|2[0-4][0-9]|[0-1]{1}[0-9]{"
   + "2}|[1-9]{1}[0-9]{1}|[1-9])\\.(25[0-5]|2[0-4][0-9]|[0-1]{1}"
   + "[0-9]{2}|[1-9]{1}[0-9]{1}|[1-9]|0)\\.(25[0-5]|2[0-4][0-9]|"
   + "[0-1]{1}[0-9]{2}|[1-9]{1}[0-9]{1}|[1-9]|0)\\.(25[0-5]|2[0-"
   + "4][0-9]|[0-1]{1}[0-9]{2}|[1-9]{1}[0-9]{1}|[0-9])|([a-zA-Z0"
   + "-9\\-]+\\.)*[a-zA-Z0-9\\-]+\\.[a-zA-Z]{2,4})(\\:[0-9]+)?(/"
   + "[^/][a-zA-Z0-9\\.\\,\\?\\'\\\\/\\+&%\\$\\=~_\\-@]*)*$"
;