Servlet：

package cn.com.seegoo.xm.front.servlets;import java.io.File;import java.io.IOException;import java.io.PrintWriter;import java.util.Iterator;import java.util.List;import javax.servlet.ServletException;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import org.apache.commons.fileupload.FileItem;import org.apache.commons.fileupload.FileUploadBase.SizeLimitExceededException;import org.apache.commons.fileupload.FileUploadException;import org.apache.commons.fileupload.disk.DiskFileItemFactory;import org.apache.commons.fileupload.servlet.ServletFileUpload;import cn.com.seegoo.servletrest.servlets.BaseServlet;public class PhotoUpServlet extends BaseServlet{ final long MAX_SIZE = 10 * 1024 * 1024;// 设置上传文件最大为 10M    // 允许上传的文件格式的列表    final String[] allowtype = new String[] {"jpg","jpeg","gif","txt","doc","docx","mp3","wma","m4a","xls"};    public PhotoUpServlet() {        super();    }    public void destroy() {        super.destroy();    }    @Override    protected void service(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException {        response.setContentType("text/html");        // 设置字符编码为UTF-8, 这样支持汉字显示        response.setCharacterEncoding("UTF-8");        // 实例化一个硬盘文件工厂,用来配置上传组件ServletFileUpload        DiskFileItemFactory dfif = new DiskFileItemFactory();        dfif.setSizeThreshold(4096);        // 设置上传文件时用于临时存放文件的内存大小,这里是4K.多于的部分将临时存在硬盘        dfif.setRepository(new File(request.getRealPath("/") + "upload"));        // 设置存放临时文件的目录,web根目录下的uploadtemp目录        // 用以上工厂实例化上传组件        ServletFileUpload sfu = new ServletFileUpload(dfif);        // 设置最大上传尺寸        sfu.setSizeMax(MAX_SIZE);        PrintWriter out = response.getWriter();        // 从request得到 所有 上传域的列表        List fileList = null;        try {            fileList = sfu.parseRequest(request);        } catch (FileUploadException e) {// 处理文件尺寸过大异常            if (e instanceof SizeLimitExceededException) {                out.println("{message:'文件尺寸超过规定大小:"+MAX_SIZE+"字节'}");                return;            }            e.printStackTrace();        }        // 没有文件上传        if (fileList == null || fileList.size() == 0) {            out.println("{message:'请选择上传文件'}");            return;        }        // 得到所有上传的文件        Iterator fileItr = fileList.iterator();        // 循环处理所有文件        while (fileItr.hasNext()) {            FileItem fileItem = null;            String path = null;            long size = 0;            // 得到当前文件            fileItem = (FileItem) fileItr.next();            // 忽略简单form字段而不是上传域的文件域(
    等)            if (fileItem == null || fileItem.isFormField()) {                continue;            }            // 得到文件的完整路径            path = fileItem.getName();            // 得到文件的大小            size = fileItem.getSize();            if ("".equals(path) || size == 0) {                out.println("{message:'请选择上传文件'}");                return;            }            // 得到去除路径的文件名            String t_name = path.substring(path.lastIndexOf("\\") + 1);            // 得到文件的扩展名(无扩展名时将得到全名)            String t_ext = t_name.substring(t_name.lastIndexOf(".") + 1);            // 拒绝接受规定文件格式之外的文件类型            int allowFlag = 0;            int allowedExtCount = allowtype.length;            for (; allowFlag < allowedExtCount; allowFlag++) {                if (allowtype[allowFlag].equals(t_ext))                    break;            }            if (allowFlag == allowedExtCount) {                String message = "";                for (allowFlag = 0; allowFlag < allowedExtCount; allowFlag++){                    message+="*." + allowtype[allowFlag]                                                + " ";                }                out.println("{message:'请上传以下类型的文件"+message+"'}");                return;            }            long now = System.currentTimeMillis();            // 根据系统时间生成上传后保存的文件名            String prefix = String.valueOf(now);            // 保存的最终文件完整路径,保存在web根目录下的upload目录下            String u_name = request.getRealPath("/") + "upload/"                    + prefix + "." + t_ext;            //原来的文件名            path=request.getRealPath("/") + "upload/"+path;            try {                // 保存文件                fileItem.write(new File(path));                response.setStatus(200);                out.println("{message:\"文件上传成功. 已保存为: " + prefix + "." + t_ext                        + " 文件大小: " + size + "字节\"}");            } catch (Exception e) {                e.printStackTrace();            }        }    }}

JS：

function ajaxFileUpload()    {               $("#loading")        .ajaxStart(function(){            $(this).show();        })//开始上传文件时显示一个图片        .ajaxComplete(function(){            $(this).hide();        });//文件上传完成将图片隐藏起来               $.ajaxFileUpload        (            {                url:'PhotoUpServlet',//用于文件上传的服务器端请求地址                secureuri:false,//一般设置为false                fileElementId:'fileField',//文件上传空间的id属性  
                    dataType: 'json',//返回值类型 一般设置为json                success: function (data, status)  //服务器成功响应处理函数                {                    //alert(data.message);//从服务器返回的json中取出message中的数据,其中message为在struts2中定义的成员变量                    $('#myspan').html(data.message);                    if(typeof(data.error) != 'undefined')                    {                        if(data.error != '')                        {                            //alert(data.error);                            $('#myspan').html(data.message);                        }else                        {                            //alert(data.message);                            $('#myspan').html(data.message);                        }                    }                },                error: function (data, status, e)//服务器响应失败处理函数                {                    //alert(e);                    $('#myspan').html(e);                }            }        )               return false;    }

界面：

web.xml:

    
             
     
      PhotoUpServlet
             
     
      cn.com.seegoo.xm.front.servlets.PhotoUpServlet
         
        
    
             
     
      PhotoUpServlet
             
     
      /PhotoUpServlet