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Java实现文件上传下载功能 基于Java文件输入输出流实现文件上传下载功能

糖拌西红柿 人气:0

本文为大家分享了Java实现文件上传下载功能的具体代码,供大家参考,具体内容如下

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:

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Insert title here</title>
<script src="Js/jquery.js"></script>
</head>
<body>
 <form action="FileUpServlet" method="post" enctype="multipart/form-data">
 <table>
 <tr>
  <td>请选择上传文件:</td><td><input id="myfile" name="myfile" type="file" value="" /></td>
  <td><input type="submit" value="上传"></td>
 </tr>
 <tr><td>${info}</td></tr>
 </table> 
 </form>
  文件下载:<a href="FileLoadownServlet?filename=${filename}">${filename}</a>
</body>
</html>

上传servlet部分(核心)

@WebServlet("/FileUpServlet")
public class FileUpServlet extends HttpServlet {
 private static final long serialVersionUID = 1L;
  
 /**
  * @see HttpServlet#HttpServlet()
  */
 public FileUpServlet() {
  super();
  // TODO Auto-generated constructor stub
 }

 /**
  * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
  */
 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  // TODO Auto-generated method stub
  doPost(request, response);
 }

 /**
  * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
  */
 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  // TODO Auto-generated method stub
  request.setCharacterEncoding("utf-8");
  InputStream filesource = request.getInputStream();//request获取流信息
  String tempname = "D:/temp";//tempfile代表临时存放文件
  File tempfile = new File(tempname);//创建临时文件
  
  FileOutputStream outputStream = new FileOutputStream(tempfile);//输出流对象,指定输出指tempfile目录下
  byte b[] = new byte[1024];
  int n;
  while((n = filesource.read(b))!= -1)//从输出流中每次读取1024字节,直至读完
  {
   outputStream.write(b,0,n);
  }
  outputStream.close();
  filesource.close();//关闭输入输出流
  
  
  /*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!*/
  

  RandomAccessFile randomfile = new RandomAccessFile(tempfile, "r");//随机流,指定要读临时文件,只读
  randomfile.readLine();//读取第一行,无效数据,不需要
  String str = randomfile.readLine();//读取第二行
  int beginIndex = str.lastIndexOf("=")+2;//指定所需数据的开始位置
  int endIndex = str.lastIndexOf("\"");//指定所需数据截至位置
  String filename = str.substring(beginIndex,endIndex);//截取文件名
  
  //重新定位文件指针,获取文件内容
  randomfile.seek(0);//文件指针从头开始
  long startext = 0;
  int i = 1;
  //文件内容开始位置
  while((n=randomfile.readByte()) != -1&&i <= 4)
  {
   if(n=='\n')
   {
    startext = randomfile.getFilePointer();
    i++;
   } 
  }
  startext = randomfile.getFilePointer() - 1;
  //获取文件内容 结束位置
  randomfile.seek(randomfile.length());
  long endtext = randomfile.getFilePointer();
  int j = 1;
  while(endtext >= 0 && j <= 2)
  {
   endtext--;
   randomfile.seek(endtext);
   if(randomfile.readByte()=='\n')
   {
    j++;
   }
  }
  endtext = endtext-1;
  
  //将临时文件保存至指定目录中 
  String realpath = getServletContext().getRealPath("/")+"images";//设置文件保存目录
  System.out.println(realpath);
  File fileupload = new File(realpath);
  if(!fileupload.exists())
  {
   fileupload.mkdir();//目录不存在则创建
  }
  File savefile = new File(realpath,filename);
  RandomAccessFile randomAccessFile = new RandomAccessFile(savefile, "rw");
  randomfile.seek(startext);
  while(startext<endtext){
   randomAccessFile.write(randomfile.readByte());//文件写入
   startext = randomfile.getFilePointer();
  }
  //关闭各种输入输出流
  randomAccessFile.close();
  randomfile.close();
  tempfile.delete();//删除临时文件
  
  
  SimpleDateFormat timed = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
  Date nowdate = new Date();
  String time = timed.format(nowdate.getTime());
  request.setAttribute("info", time+" "+filename+"上传成功!");
  request.setAttribute("filename", filename);
  request.getRequestDispatcher("/fildeOp.jsp").forward(request, response);
 }

}

下载部分

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

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