一个简单的jQuery插件ajaxfileupload实现ajax上传文件例子
    页面代码:
<html>
    <!-- 引入相关的js文件,相对路径  -->
    <script type="text/javascript" src="js/jquery.js"></script>
      <script type="text/javascript" src="js/ajaxfileupload.js"></script>
    <!-- 执行上传文件操作的函数 -->
      <script type="text/javascript">
          function ajaxFileUpload(){
               $.ajaxFileUpload(
                   {
                url:'update.do?method=uploader',            //需要链接到服务器地址
                secureuri:false,
                fileElementId:'houseMaps',                        //文件选择框的id属性
                dataType: 'xml',                                     //服务器返回的格式,可以是json
                success: function (data, status)            //相当于java中try语句块的用法
                {      
                    $('#result').html('添加成功');
                },
                error: function (data, status, e)            //相当于java中catch语句块的用法
                {
                    $('#result').html('添加失败');
                }
            }                   
               );              
          }
      </script>
  </head>  
  <body>
      <form method="post" action="update.do?method=uploader" enctype="multipart/form-data">  
        <input type="file" id="houseMaps" name="houseMaps"/> 
        <input type="button" value="提交" onclick="ajaxFileUpload()"/>
    </form> 
    <div id="result"></div>    
  </body>
</html>
服务器代码:
public class