jsp实现文件上传下载的程序示例

<form action="file?file=upload" method="post" enctype="multipart/form-data">
    请选择你要上传的文件：<input type="file" name="upload" siez="16"><br>
    <input type="submit" value="提交">
  </form>

//接收上传文件内容中临时文件的文件名
        String tempFileName = new String("tempFileName");
        //tempfile 对象指向临时文件
        File tempFile = new File("D:/"+tempFileName);
        //outputfile 文件输出流指向这个临时文件
        FileOutputStream outputStream = new FileOutputStream(tempFile);
        //得到客服端提交的所有数据
        InputStream fileSourcel = request.getInputStream();
        //将得到的客服端数据写入临时文件
        byte b[] = new byte[1000];
        int n ;
        while ((n=fileSourcel.read(b))!=-1){
            outputStream.write(b,0,n);
        }

        //关闭输出流和输入流
        outputStream.close();
        fileSourcel.close();

        //randomFile对象指向临时文件
        RandomAccessFile randomFile = new RandomAccessFile(tempFile,"r");
        //读取临时文件的第一行数据
        randomFile.readLine();
        //读取临时文件的第二行数据，这行数据中包含了文件的路径和文件名
        String filePath = randomFile.readLine();
        //得到文件名
        int position = filePath.lastIndexOf('\\');
        CodeToString codeToString = new CodeToString();
        String filename = codeToString.codeString(filePath.substring(position,filePath.length()-1));
        //重新定位读取文件指针到文件头
        randomFile.seek(0);
        //得到第四行回车符的位置，这是上传文件数据的开始位置
        long  forthEnterPosition = 0;
        int forth = 1;
        while((n=randomFile.readByte())!=-1&&(forth<=4)){
            if(n=='\n'){
                forthEnterPosition = randomFile.getFilePointer();
                forth++;
            }
        }

        //生成上传文件的目录
        File fileupLoad = new File("D:/work space/JSP workspace/jsp_servlet_upAndLoad/file","upLoad");
        fileupLoad.mkdir();
        //saveFile 对象指向要保存的文件
        File saveFile = new File("D:/work space/JSP workspace/jsp_servlet_upAndLoad/file/upLoad",filename);
        RandomAccessFile randomAccessFile = new RandomAccessFile(saveFile,"rw");
        //找到上传文件数据的结束位置，即倒数第四行
        randomFile.seek(randomFile.length());
        long endPosition = randomFile.getFilePointer();
        int j = 1;
        while((endPosition>=0)&&(j<=4)){
            endPosition--;
            randomFile.seek(endPosition);
            if(randomFile.readByte()=='\n'){
                j++;
            }
        }

        //从上传文件数据的开始位置到结束位置，把数据写入到要保存的文件中
        randomFile.seek(forthEnterPosition);
        long startPoint = randomFile.getFilePointer();
        while(startPoint<endPosition){
            randomAccessFile.write(randomFile.readByte());
            startPoint = randomFile.getFilePointer();
        }
        //关闭文件输入、输出
        randomAccessFile.close();
        randomFile.close();
        tempFile.delete();

//处理中文字符串的函数
    public String codeString(String str){
        String s = str;
        try {
            byte[] temp = s.getBytes("utf-8");
            s = new String(temp);
            return s ;
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
            return s;
        }
    }

//获取要下载的文件名
        String filename = request.getParameter("name");
        //得到想客服端输出的输出流
        OutputStream outputStream = response.getOutputStream();
        //输出文件用的字节数组，每次向输出流发送600个字节
        byte b[] = new byte[600];
        //要下载的文件
        File fileload = new File("D:/work space/JSP workspace/jsp_servlet_upAndLoad/file/upLoad",filename);       
        //客服端使用保存文件的对话框
        response.setHeader("Content-disposition", "attachment;filename="+filename);
        //通知客服文件的MIME类型
        response.setContentType("application/msword");
        //通知客服文件的长度
        long fileLength = fileload.length();
        String length = String.valueOf(fileLength);
        response.setHeader("Content_length", length);
        //读取文件，并发送给客服端下载
        FileInputStream inputStream = new FileInputStream(fileload);
        int n = 0;
        while((n=inputStream.read(b))!=-1){
            outputStream.write(b,0,n);
        }