public class RegisterServlet extends HttpServlet {
  private static final long serialVersionUID = 1L;
  public RegisterServlet() {
    super();
  }
  protected void doGet(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
    response.getWriter().append("Served at: ").append(request.getContextPath());
  }
  protected void doPost(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
    //第一步、判斷請求是否為multipart請求
    if(!ServletFileUpload.isMultipartContent(request)) {
      throw new RuntimeException("當前請求只支持文件上傳");
    }
    try {
      //第二步、創建FileItem工廠
      DiskFileItemFactory factory = new DiskFileItemFactory();
      //設置臨時文件存儲目錄
      String path = this.getServletContext().getRealPath("/Temp");
      File temp = new File(path);
      factory.setRepository(temp);
      //單位：字節。本例設置邊界值為2MB，超過該值會創建臨時文件
      factory.setSizeThreshold(1024*1024*2);
      //第三步、創建文件上傳核心組件
      ServletFileUpload upload = new ServletFileUpload(factory);
      //設置item的頭部字符編碼，解決中文亂碼問題
      upload.setHeaderEncoding("utf-8");
      //設置單個上傳文件的最大值為5MB
      upload.setFileSizeMax(1024*1024*5);
      //設置一次上傳所有文件總和的最大值為10MB（上傳多個文件時起作用）
      upload.setFileSizeMax(1024*1024*10);
      //第四步、解析請求獲取所有的item
      List<FileItem> items = upload.parseRequest(request);
      //第五步、遍歷item
      for(FileItem item:items) {
        if (item.isFormField()) {
            processFormField(item);
          } else {
            processUploadedFile(item);
          }
      }
    } catch (FileUploadException e) {
      e.printStackTrace();
    }
  }
  private void processFormField(FileItem item) {
    try {
      String name = item.getFieldName();
      //解決中文亂碼問題
      String value = item.getString("utf-8");
      System.out.println(name+"="+value);
    } catch (UnsupportedEncodingException e) {
      e.printStackTrace();
    }
  }
  private void processUploadedFile(FileItem item) {
    try {
      InputStream inputStream = item.getInputStream();
      String fieldName = item.getFieldName();
      //獲取上傳文件原始名稱
      String fileName = item.getName();
      //解決文件同名問題
      fileName = System.currentTimeMillis()+fileName;
      String contentType = item.getContentType();
      boolean isInMemory = item.isInMemory();
      long sizeInBytes = item.getSize();
      String path = this.getServletContext().getRealPath("/UploadContent");
      //Date now = new Date();
      Calendar now = Calendar.getInstance();
      //對上傳的文件進行分類管理
      path += "/"+now.get(Calendar.YEAR)+"/"+(now.get(Calendar.MONTH)+1)+"/"+now.get(Calendar.DAY_OF_MONTH);
      //若目錄不存在，則創建該目錄
      File directory = new File(path);
      if(!directory.exists()) {
        directory.mkdirs();
      }
      File descFile = new File(path,fileName);
      OutputStream outputStream = new FileOutputStream(descFile);
      int length = -1;
      byte[] buffer = new byte[1024];
      while((length=inputStream.read(buffer))!=-1) {
        outputStream.write(buffer, 0, length);
      }
      outputStream.close();
      inputStream.close();
      //刪除臨時文件
      item.delete();
    } catch (IOException e) {
      e.printStackTrace();
    }
  }
}

public class DownloadServlet extends HttpServlet {
  private static final long serialVersionUID = 1L;
  public DownloadServlet() {
    super();
  }
  protected void doGet(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
    //設置響應的頭部屬性content-disposition值為attachment
    //使用filename來指定文件名
    String filename = "超跑.png";
    byte[] bytes = filename.getBytes("utf-8");
    //http協議規定瀏覽器只能接受ISO8859-1類型的字節數據
    filename = new String(bytes,"ISO8859-1");
    response.setHeader("content-disposition", "attachment;filename="+filename);
    //獲取連接服務器資源文件的輸入流
    InputStream is = request.getServletContext().getResourceAsStream("/Resources/BS架構原理圖1.png");
    //獲取輸出流
    ServletOutputStream os = response.getOutputStream();
    //將輸入流中的數據寫到輸出流中
    int length = -1;
    byte[] buffer = new byte[1024];
    while((length=is.read(buffer))!=-1) {
      os.write(buffer,0,length);
    }
    os.close();
    is.close();
  }
  protected void doPost(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
    doGet(request, response);
  }
}