文本框设置为多行显现，MaxLength无效，只能另外写方法控制，可用下列两个JS函数，超过长度自动截断，引用时方法：onkeypress="return checkMaxLength(this);" onkeyup="checkLength(this);"

    function checkLength(which) {
    if(which!=null&&which!=""&&which!=undefined)
    {
        var maxChars = 500;
        if (which.value.length > maxChars)
        which.value = which.value.substring(0,maxChars);
    }
    }

    function checkMaxLength(which)
    {
        var maxChars = 500;
        if (which.value.length > maxChars)
        return false;
    }