使用commons-fileupload实现单个和多个文件上传

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对于实现文件上传功能来说，Commons-fileupload组件是一个不错的选择，本文使用它实现了单个文件及多个文件上传，这里将实现过程写出来与大家共享。

1.单个文件上传。
页面代码：

<!-- <br /> <br /> Code highlighting produced by Actipro CodeHighlighter (freeware)<br /> http://www.CodeHighlighter.com/<br /> <br /> -->        
.... < div  id ="content" >
             < fieldset >< legend > 下載列表 </ legend >
                 < ul >
                 <%
                    List < String >  downloadList = (List < String > )request.getAttribute( " downloadList " );    
                    
                     if (downloadList! = null ){
                         for ( String  str:downloadList){    
                            out.print( " <li><a href='DownloadFile?file= " + str + " '> " + str + " </a></li> " );
                        }
                    }
                 %>
                 </ ul >
             </ fieldset >
        
             <!--  enctype属性为表单定义了MIME编码方式，上传文件的表单enctype属性必须如此设置  -->
             < form  method ="post"  action ="UploadFile"  enctype ="multipart/form-data"   >
             < p >< input  type ="text"  name ="fileIntro"  value =""   /> 文件介绍 </ p >
             < p >< input  type ="file"  name ="myfile1"  value ="浏览文件"   /></ p >
             < p >< input  type ="submit"  value ="上传" /></ p >
             </ form >
         </ div >....

在上传表单中，既有普通文本域也有文件上传域，注意在Servlet中取它们和平常的做法不同：
Servlet代码：

<!-- <br /> <br /> Code highlighting produced by Actipro CodeHighlighter (freeware)<br /> http://www.CodeHighlighter.com/<br /> <br /> --> package  com.sitinspring.action;

import  java.io.File;
import  java.util.ArrayList;
import  java.util.Iterator;
import  java.util.List;

import  javax.servlet.RequestDispatcher;
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.FileItemFactory;
import  org.apache.commons.fileupload.disk.DiskFileItemFactory;
import  org.apache.commons.fileupload.servlet.ServletFileUpload;

import  com.sitinspring.util.UploadUtil;

/**
 * 用于文件上传处理的Servlet
 *  @author  sitinspring
 *
 * @date 2008-2-12
  */
public   class  UploadFileServlet  extends  HttpServlet {
     private   static   final   long  serialVersionUID  =   56890894234786L ;

    @SuppressWarnings( " unchecked " )
     public   void  doPost(HttpServletRequest request, HttpServletResponse response)
             throws  ServletException, java.io.IOException {
        request.setCharacterEncoding( " UTF-8 " );

         //  文件上傳部分
         boolean  isMultipart  =  ServletFileUpload.isMultipartContent(request);
        
         if  (isMultipart  ==   true ) {
             try  {
                FileItemFactory factory  =   new  DiskFileItemFactory();
                ServletFileUpload upload  =   new  ServletFileUpload(factory);
                
                 //  得到所有的表单域，它们目前都被当作FileItem
                List < FileItem >  fileItems  =  upload.parseRequest(request);
                Iterator < FileItem >  iter  =  fileItems.iterator();
                
                 //  依次处理每个表单域
                 while  (iter.hasNext()) {
                    FileItem item  =  (FileItem) iter.next();
                    
                     if (item.isFormField()){
                         //  如果item是正常的表单域
                        String name  =  item.getFieldName();
                        String value  =  item.getString();
                        System.out.print( " 表单域名为: " + name + " 表单域值为: " + value);
                    }
                     else {
                         //  如果item是文件上传表单域
                        
                         //  获得文件名及路径
                        String fileName  =  item.getName();
                         if  (fileName  !=   null ) {
                            File fullFile  =   new  File(item.getName());                            
                                                        
                             //  如果文件存在则上传
                             if (fullFile.exists()){
                                File fileOnServer  =   new  File(UploadUtil.getUploadPath(),
                                        fullFile.getName());
                                item.write(fileOnServer);
                                
                                System.out.println( " 文件 " + fileOnServer.getName() + " 上传成功 " );
                            }
                        }
                    }
                }                
            }  catch  (Exception e) {
                e.printStackTrace();
            }
        }  else  {
            System.out.println( " the enctype must be multipart/form-data " );
        }
        
         //  取得服务器中已有文件的下載列表
        List < String >  fileListInServer = new  ArrayList < String > (); 
        
        File dir  =   new  File(UploadUtil.getUploadPath());        
        String[] children  =  dir.list();
         if  (children  !=   null ) {
             for  ( int  i = 0 ; i < children.length; i ++ ) {
                fileListInServer.add(children[i]);                
            }
        }
        
        request.setAttribute( " downloadList " , fileListInServer);

         //  跳回原頁面
        RequestDispatcher dispatcher  =  request
                .getRequestDispatcher( " /web/page/uploadtoserver.jsp " );
        dispatcher.forward(request, response);
         return ;
    }

     public   void  doGet(HttpServletRequest request, HttpServletResponse response)
             throws  ServletException, java.io.IOException {
        doPost(request, response);
    }
}

从上面的代码可以看出，无论是否文件上传表单域都被当成了FileItem来处理，要区别开来使用isFormField()方法即可，返回真是常规表单域，返回假则是文件上传表单域。

2.多个文件上传到服务器端。

这里采用JS动态生成几个文件上传表单域即可，Servlet无需改变。
多文件上传页面代码如下:

<!-- <br /> <br /> Code highlighting produced by Actipro CodeHighlighter (freeware)<br /> http://www.CodeHighlighter.com/<br /> <br /> --> <% @ page contentType = " text/html; charset=UTF-8 " %>
<% @page language = " java "  import = " java.util.List " %>

<! DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" >
< html >
< head >
< title > 上传多個文件到服务器 </ title >
< meta  http-equiv ="Content-Type"  content ="text/html; charset=UTF-8" >
< link  rel ="stylesheet"  rev ="stylesheet"  href ="web/css/style.css"
    type ="text/css"   />
</ head >

< body >
     < div  id ="bodyDiv" >
         < div  id ="header" >
             < jsp:include  page ="/web/page/branch/header.jsp" />
         </ div >
         < div  id ="sidebar" >
             < jsp:include  page ="/web/page/branch/sidebar.jsp" />
         </ div >
         < div  id ="content" >
             < fieldset >< legend > 下載列表 </ legend >
                 < ul >
                 <%
                    List < String >  downloadList = (List < String > )request.getAttribute( " downloadList " );    
                    
                     if (downloadList! = null ){
                         for ( String  str:downloadList){    
                            out.print( " <li><a href='DownloadFile?file= " + str + " '> " + str + " </a></li> " );
                        }
                    }
                 %>
                 </ ul >
             </ fieldset >
        
             <!--  enctype属性为表单定义了MIME编码方式，上传文件的表单enctype属性必须如此设置  -->
             < form  name ="uploadForm"  method ="post"  action ="UploadFile"  enctype ="multipart/form-data"   >
             < p >< input  type ="button"  value ="增加上传按钮"  onclick ="addUploadButton()" /></ p >
             < p >< input  type ="file"  name ="myfile1"  value ="浏览文件"   /></ p >
             < p >< input  type ="submit"  value ="上传" /></ p >
             </ form >
         </ div >
         < div  id ="footer" >
             < jsp:include  page ="/web/page/branch/footer.jsp" />
         </ div >
     </ div >
</ body >

JS代码：

<!-- <br /> <br /> Code highlighting produced by Actipro CodeHighlighter (freeware)<br /> http://www.CodeHighlighter.com/<br /> <br /> --> < script LANGUAGE = " JavaScript " >
<!--
var  count = 1 ;

function  addUploadButton(){    
     //  按ID找到FOrm
     var  uploadForm = document.getElementById( " uploadForm " );    
    
     //  创建P元素
     var  pNode = document.createElement( " p " );
    
     //  累加Count以观察次数
    count = count + 1 ;
    
    pNode.innerHTML = " <input type='file' name='myfile " + count + " ' value='浏览文件'/> " ;
    
     //  将P元素添加到body中
    uploadForm.appendChild(pNode);
}

// -->
</ script >
</ html >