//判断照片大小

function getPhotoSize(obj){

    photoExt=obj.value.substr(obj.value.lastIndexOf(".")).toLowerCase();//获得文件后缀名

    if(photoExt!='.jpg'){

        alert("请上传后缀名为jpg的照片!");

        return false;

    }

    var fileSize = 0;

    var isIE = /msie/i.test(navigator.userAgent) && !window.opera;

    if (isIE && !obj.files) {

         var filePath = obj.value;

         var fileSystem = new ActiveXObject("Scripting.FileSystemObject");

         var file = fileSystem.GetFile (filePath);

         fileSize = file.Size;

    }else {

         fileSize = obj.files[0].size;

    }

    fileSize=Math.round(fileSize/1024*100)/100; //单位为KB

    if(fileSize>=10){

        alert("照片最大尺寸为10KB，请重新上传!");

        return false;

    }

}

jsp页面：

<input type="file" id="imgFile" name="upload" style="width:150px;" onchange="getPhotoSize(this)"/>