jsp中点击图片弹出文件上传界面及预览功能的实现

!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
html>
head>
meta http-equiv="Content-Type" content="text/html; charset=utf-8">
title>Insert title here/title>
script type="text/javascript">
function tempClick(){

/**
* 火狐浏览器实现点击图片出现文件上传界面
* var a=document.createEvent("MouseEvents");
* a.initEvent("click", true, true);
* document.getElementById("upload_main_img").dispatchEvent(a);
*/

//IE浏览器实现点击图片出现文件上传界面
document.getElementById('main_img').click(); //调用main_img的onclick事件
}

/**
* 预览图片
* @param obj
* @returns {Boolean}
*/
function PreviewImg(obj) {

var newPreview = document.getElementById("img_2");
var imgPath = getPath(obj);
alert(imgPath);
if( !obj.value.match( /.jpg|.gif|.png|.bmp/i ) ){
alert("图片格式错误！");
return false;
}

newPreview.style.filter = "progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=scale)";
newPreview.filters.item("DXImageTransform.Microsoft.AlphaImageLoader").src = imgPath;
}

/**
* 得到图片绝对路径
* @param obj
* @returns
*/
function getPath(obj){
if(obj) {
if(navigator.userAgent.indexOf("MSIE")>0) {
obj.select();
//IE下取得图片的本地路径
return document.selection.createRange().text;
} else if(isFirefox=navigator.userAgent.indexOf("Firefox")>0) {
if (obj.files) { // Firefox下取得的是图片的数据
return files.item(0).getAsDataURL();
}
return obj.value;
}
return obj.value;
}
}
/script>
/head>
body>
form>
div>input type="file" style="position: absolute; filter: alpha(opacity = 0); opacity: 0; width: 30px;" size="1" id="main_img" name="main_img" onchange="PreviewImg(this)">/div>
div id="img_2" style="width:133px;height:95px; cursor:pointer; background-image: url('Chrysanthemum.jpg');" onclick="tempClick()">/div>
/form>
/body>
/html>