jQuery插件AjaxFileUpload用来实现ajax文件上传，该插件使用非常简单，接下来写个demo演示怎么用AjaxFileUpload插件实现文件上传。
1、引入AjaxFileUpload插件相关的js
<script type="text/javascript" src="<%=basePath%>resources/js/jquery-1.2.1.js"></script>
<script type="text/javascript" src="<%=basePath%>resources/js/ajaxfileupload.js"></script>备注：测试发现，ajaxfileupload对jQuery版本是有要求的，在使用中ajaxfileupload和jQuery对应的js版本要一致，不然会导致异常发生，可以从ajaxfileupload官网下载，避免版本冲突。
2、实现上传功能代码
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@ include file="/base.jsp" %>
<% String path = request.getContextPath(); String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>ajax文件上传</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<link rel="stylesheet" type="text/css" href="validate/ajaxfileupload.css" />
<script type="text/javascript" src="validate/jquery-1.6.2.min.js"></script>
<script type="text/javascript" src="validate/ajaxfileupload.js" ></script>
<script type="text/javascript"> $(function(){ //上传图片
$("#btnUpload").click(function() { alert(ajaxFileUpload()); }); }); function ajaxFileUpload() { // 开始上传文件时显示一个图片
$("#wait_loading").ajaxStart(function() { $(this).show(); // 文件上传完成将图片隐藏起来
}).ajaxComplete(function() { $(this).hide(); }); var elementIds=["flag"]; //flag为id、name属性名
$.ajaxFileUpload({ url: 'uploadAjax.htm', type: 'post', secureuri: false, //一般设置为false
fileElementId: 'file', // 上传文件的id、name属性名
dataType: 'text', //返回值类型，一般设置为json、application/json
elementIds: elementIds, //传递参数到服务器
success: function(data, status){ alert(data); }, error: function(data, status, e){ alert(e); } }); //return false;
} </script>
</head>
<body>
<div id="wait_loading" style="padding: 50px 0 0 0;display:none;">
<div style=" 103px;margin: 0 auto;"><img src="<%=path %>/images/loading.gif"/></div>
<br></br>
<div style=" 103px;margin: 0 auto;"><span>请稍等...</span></div>
<br></br>
</div>
<input type="file" id="file" name="file"><br/>
<input type="hidden" id="flag" name="flag" value="ajax文件上传"/>
<input type="button" id="btnUpload" value="上传图片" />
</body>
</html>