java基于servlet的文件异步上传

package com.future.zfs.util;

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.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.FileUploadBase.SizeLimitExceededException;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;

@SuppressWarnings("serial")
public class FileUploadServlet extends HttpServlet {

  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 FileUploadServlet() {
    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("/")
        + "uploadtemp"));// 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(<input type="text" />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();
      }

    }
  }
}

<servlet>
    <servlet-name>fileUploadServlet</servlet-name>
    <servlet-class>com.future.zfs.util.FileUploadServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>fileUploadServlet</servlet-name>
    <url-pattern>/fileUploadServlet</url-pattern>
  </servlet-mapping>

<%@ page language="java" contentType="text/html; charset=UTF-8"
  pageEncoding="UTF-8"%>
<!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" src="js/jquery.js"></script>
    <script type="text/javascript" src="js/ajaxfileupload.js"></script>
    <script type="text/javascript">
  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:'fileUploadServlet',//用于文件上传的服务器端请求地址
        secureuri:false,//一般设置为false
        fileElementId:'file',//文件上传空间的id属性 <input type="file" id="file" name="file" />
        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;

  }
  </script>
  </head>
  <body>
    <img src="images/loading.gif" id="loading" style="display: none;">
    <span style="color: red;" id="myspan"></span><br/>
    <input type="file" id="file" name="file" />
    <br />
    <input type="button" value="上传" onclick="return ajaxFileUpload();">
    <a href="fileDownLoadServlet?filename=通讯录.xls">哈哈，测试文件下载</a>
  </body>
</html>