Java文件上传下载

基于Java文件输入输出流的文件上传下载功能实现

原理：前端通过form表单的enctype属性，将数据传递方式修改为二进制”流“的形式，服务端（servlet）通过 getInputStream() 获取流信息，运用java I/O 流的基础操作将流写入到一个服务端临时创建的文件temp中，然后再次利用文件基本操作，读取并截取临时文件内容，根据其中信息创建相应的文件，将读取出来的具体信息写入，下载时，根据提交的文件名称，找到服务器端相应的文件，然后根据输出流outStream输出到页面，同时将servlet的响应类型和响应头进行设置。

具体传输流程如下图：

流信息的部分为：

具体代码如下：

前端代码：

 1 <html>
 2 <head>
 3 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
 4 <title>Insert title here</title>
 5 <script src="Js/jquery.js"></script>
 6 </head>
 7 <body>
 8   <form action="FileUpServlet" method="post" enctype="multipart/form-data">
 9    <table>
10     <tr>
11       <td>请选择上传文件:</td><td><input id="myfile" name="myfile" type="file" value="" /></td>
12       <td><input type="submit" value="上传"></td>
13     </tr>
14     <tr><td>${info}</td></tr>
15    </table> 
16   </form>
17         文件下载：<a href="FileLoadownServlet?filename=${filename}">${filename}</a>
18 </body>
19 </html>

View Code

上传servlet部分（核心）

  1 @WebServlet("/FileUpServlet")
  2 public class FileUpServlet extends HttpServlet {
  3     private static final long serialVersionUID = 1L;
  4        
  5     /**
  6      * @see HttpServlet#HttpServlet()
  7      */
  8     public FileUpServlet() {
  9         super();
 10         // TODO Auto-generated constructor stub
 11     }
 12 
 13     /**
 14      * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
 15      */
 16     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 17         // TODO Auto-generated method stub
 18         doPost(request, response);
 19     }
 20 
 21     /**
 22      * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
 23      */
 24     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 25         // TODO Auto-generated method stub
 26         request.setCharacterEncoding("utf-8");
 27         InputStream filesource = request.getInputStream();//request获取流信息
 28         String tempname = "D:/temp";//tempfile代表临时存放文件
 29         File tempfile = new File(tempname);//创建临时文件
 30         
 31         FileOutputStream outputStream = new FileOutputStream(tempfile);//输出流对象，指定输出指tempfile目录下
 32         byte b[] = new byte[1024];
 33         int n;
 34         while((n = filesource.read(b))!= -1)//从输出流中每次读取1024字节,直至读完
 35         {
 36             outputStream.write(b,0,n);
 37         }
 38         outputStream.close();
 39         filesource.close();//关闭输入输出流
 40         
 41         
 42         /*以下为具体的文件操作，主要为解析临时产生的 temp文件 ，知识多为java输入输出流的内容！*/
 43         
 44 
 45         RandomAccessFile randomfile = new RandomAccessFile(tempfile, "r");//随机流，指定要读临时文件，只读
 46         randomfile.readLine();//读取第一行,无效数据，不需要
 47         String str = randomfile.readLine();//读取第二行
 48         int beginIndex = str.lastIndexOf("=")+2;//指定所需数据的开始位置
 49         int endIndex = str.lastIndexOf("\"");//指定所需数据截至位置
 50         String filename = str.substring(beginIndex,endIndex);//截取文件名
 51         
 52         //重新定位文件指针，获取文件内容
 53         randomfile.seek(0);//文件指针从头开始
 54         long startext = 0;
 55         int i = 1;
 56         //文件内容开始位置
 57         while((n=randomfile.readByte()) != -1&&i <= 4)
 58         {
 59             if(n=='\n')
 60             {
 61                 startext = randomfile.getFilePointer();
 62                 i++;
 63             }    
 64         }
 65         startext = randomfile.getFilePointer() - 1;
 66         //获取文件内容 结束位置
 67         randomfile.seek(randomfile.length());
 68         long endtext = randomfile.getFilePointer();
 69         int j = 1;
 70         while(endtext >= 0 && j <= 2)
 71         {
 72             endtext--;
 73             randomfile.seek(endtext);
 74             if(randomfile.readByte()=='\n')
 75             {
 76                 j++;
 77             }
 78         }
 79         endtext = endtext-1;
 80         
 81         //将临时文件保存至指定目录中 
 82         String realpath = getServletContext().getRealPath("/")+"images";//设置文件保存目录
 83         System.out.println(realpath);
 84         File fileupload = new File(realpath);
 85         if(!fileupload.exists())
 86         {
 87             fileupload.mkdir();//目录不存在则创建
 88         }
 89         File savefile = new File(realpath,filename);
 90         RandomAccessFile randomAccessFile = new RandomAccessFile(savefile, "rw");
 91         randomfile.seek(startext);
 92         while(startext<endtext){
 93             randomAccessFile.write(randomfile.readByte());//文件写入
 94             startext = randomfile.getFilePointer();
 95         }
 96         //关闭各种输入输出流
 97         randomAccessFile.close();
 98         randomfile.close();
 99         tempfile.delete();//删除临时文件
100         
101         
102         SimpleDateFormat timed = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
103         Date nowdate = new Date();
104         String time = timed.format(nowdate.getTime());
105         request.setAttribute("info", time+" "+filename+"上传成功！");
106         request.setAttribute("filename", filename);
107         request.getRequestDispatcher("/fildeOp.jsp").forward(request, response);
108     }
109 
110 }

下载部分

 1 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 2         // TODO Auto-generated method stub
 3         String filename = request.getParameter("filename");
 4         String path = getServletContext().getRealPath("/")+"images/";
 5         File file = new File(path+filename);//找到文件
 6         if(file.exists())
 7         {
 8             response.setContentType("application/x-msdownload"); //设置响应类型,此处为下载类型
 9             response.setHeader("Content-Disposition", "attachment;filename=\""+filename+"\"");//以附件的形式打开
10             InputStream inputStream = new FileInputStream(file);
11             ServletOutputStream outputStream = response.getOutputStream();
12             byte b[] = new byte[1024];
13             int n;
14             while((n = inputStream.read(b)) != -1)
15             {
16                 outputStream.write(b,0,n);
17             }
18             outputStream.close();
19             inputStream.close();            
20           }else{
21             request.setAttribute("result", "文件不存在！下载失败！");
22             request.getRequestDispatcher("/fildeOp.jsp").forward(request, response);
23         }
24     }

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