<div class="center"><textarea name="salesOrderComment" onpropertychange="checkMaxLen(this,300,0)" cols="60" rows="5"  style="width:500px;">${checkoutModel.salesOrderComment }</textarea></div

<script language=javascript>
  var oldValue=new Array();
  function checkMaxLen(obj,maxlength,num){
   if(obj.value.length>maxlength){
    obj.value=oldValue[num];
   }
   else{
    oldValue[num]=obj.value;
   }
  }
 </script>

?以上就可以控制输入的字数。?