Upload và download file lưu trữ trên ổ cứng với Java Servlet

package org.o7planning.servletexamples;

import java.io.File;
import java.io.IOException;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.MultipartConfig;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.Part;

@WebServlet("/uploadFile")
@MultipartConfig(fileSizeThreshold = 1024 * 1024 * 2, // 2MB
       maxFileSize = 1024 * 1024 * 10, // 10MB
       maxRequestSize = 1024 * 1024 * 50) // 50MB
public class UploadFileServlet extends HttpServlet {
   private static final long serialVersionUID = 1L;

   public static final String SAVE_DIRECTORY = "uploadDir";

   public UploadFileServlet() {
       super();
   }

   @Override
   protected void doGet(HttpServletRequest request, HttpServletResponse response)
           throws ServletException, IOException {

       RequestDispatcher dispatcher = request.getServletContext().getRequestDispatcher("/WEB-INF/jsps/uploadFile.jsp");

       dispatcher.forward(request, response);
   }

   @Override
   protected void doPost(HttpServletRequest request, HttpServletResponse response)
           throws ServletException, IOException {
       try {
           String description = request.getParameter("description");
           System.out.println("Description: " + description);

 
           // Đường dẫn tuyệt đối tới thư mục gốc của web app.
           String appPath = request.getServletContext().getRealPath("");
           appPath = appPath.replace('\\', '/');

 
           // Thư mục để save file tải lên.
           String fullSavePath = null;
           if (appPath.endsWith("/")) {
               fullSavePath = appPath + SAVE_DIRECTORY;
           } else {
               fullSavePath = appPath + "/" + SAVE_DIRECTORY;
           }

 
           // Tạo thư mục nếu nó không tồn tại.
           File fileSaveDir = new File(fullSavePath);
           if (!fileSaveDir.exists()) {
               fileSaveDir.mkdir();
           }
 
           // Danh mục các phần đã upload lên (Có thể là nhiều file).
           for (Part part : request.getParts()) {
               String fileName = extractFileName(part);
               if (fileName != null && fileName.length() > 0) {
                   String filePath = fullSavePath + File.separator + fileName;
                   System.out.println("Write attachment to file: " + filePath);
 
                   // Ghi vào file.
                   part.write(filePath);
               }
           }
 
           // Upload thành công.
           response.sendRedirect(request.getContextPath() + "/uploadFileResults");
       } catch (Exception e) {
           e.printStackTrace();
           request.setAttribute("errorMessage", "Error: " + e.getMessage());
           RequestDispatcher dispatcher = getServletContext().getRequestDispatcher("/WEB-INF/jsps/uploadFile.jsp");
           dispatcher.forward(request, response);
       }
   }

   private String extractFileName(Part part) {
       // form-data; name="file"; filename="C:\file1.zip"
       // form-data; name="file"; filename="C:\Note\file2.zip"
       String contentDisp = part.getHeader("content-disposition");
       String[] items = contentDisp.split(";");
       for (String s : items) {
           if (s.trim().startsWith("filename")) {
               // C:\file1.zip
               // C:\Note\file2.zip
               String clientFileName = s.substring(s.indexOf("=") + 2, s.length() - 1);
               clientFileName = clientFileName.replace("\\", "/");
               int i = clientFileName.lastIndexOf('/');
               // file1.zip
               // file2.zip
               return clientFileName.substring(i + 1);
           }
       }
       return null;
   }

}

package org.o7planning.servletexamples;

import java.io.IOException;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/uploadFileResults")
public class UploadFileResultsServlet extends HttpServlet {
   private static final long serialVersionUID = 1L;


   public UploadFileResultsServlet() {
       super();
   }

   @Override
   protected void doGet(HttpServletRequest request, HttpServletResponse response)
           throws ServletException, IOException {

       RequestDispatcher dispatcher
           = request.getServletContext().getRequestDispatcher("/WEB-INF/jsps/uploadFileResults.jsp");

       dispatcher.forward(request, response);
   }

}

<!DOCTYPE >
<html>
<head>
<title>Upload files</title>
</head>
<body>

    <div style="padding:5px; color:red;font-style:italic;">
       ${errorMessage}
    </div>
   
    <h2>Upload Files</h2>

    <form method="post" action="${pageContext.request.contextPath}/uploadFile"
        enctype="multipart/form-data">
       
        Select file to upload:
        <br />
        <input type="file" name="file"  />
        <br />
        <input type="file" name="file" />
        <br />
        Description:
        <br />
        <input type="text" name="description" size="100" />
        <br />
        <br />
        <input type="submit" value="Upload" />
    </form>
   
</body>
</html>

<!DOCTYPE >
<html>
<head>
<title>Upload files</title>
</head>
<body>

    <h3>Upload has been done successfully!</h3>
    <a href="${pageContext.request.contextPath}/uploadFile">Continue Upload</a>
     
   
</body>
</html>