3a. Create a servlet application to upload and download a file.

****** Download *****



package servlet;


import java.io.IOException;
import java.io.InputStream;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet(name = "FileDownloadServlet", urlPatterns = {"/FileDownloadServlet"})
public class FileDownloadServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String fileToDownload = request.getParameter("filename");
        System.err.println("Downloading file now...");
        downloadFile(request, response, fileToDownload);
    }
   
    private void downloadFile(HttpServletRequest request, HttpServletResponse response, String fileName) throws ServletException, IOException {
        int lenght = 0;
        try (ServletOutputStream outputStream = response.getOutputStream()) {
            ServletContext context = getServletConfig().getServletContext();
            response.setContentType((context.getMimeType(fileName) != null) ? context.getMimeType(fileName) : "application/pdf");

            response.setHeader("Content-Disposition", "attachment; filename=\"" + fileName);
            InputStream inputStream = context.getResourceAsStream("/" + fileName);
            byte[] bytes = new byte[1024];
           
            while((inputStream != null) && ((lenght = inputStream.read(bytes)) != -1)) {
                outputStream.write(bytes, 0, lenght);
            }
            outputStream.flush();
        }
    }
}





***** Upload *****


<h1>File Upload Application</h1>
        <form action="FileUploadServlet" enctype="multipart/form-data" method="POST">
            File: <input type="file" name="file" id="file"/><br/><br/>
            Destination: <input type="text" value="" name="destination" /><br/><br/>
            <input type="submit" value="Upload File" name="upload" id="upload"/>
        </form>








*****FileUploadServlet.java*****


package servlet;



import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintWriter;
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(urlPatterns = {"/FileUploadServlet"})

@MultipartConfig
public class FileUploadServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");

        final String path = request.getParameter("destination");
        final Part filePart = request.getPart("file");
        final String fileName = retrieveFileName(filePart);

        OutputStream out = null;
        InputStream filecontent = null;
        final PrintWriter writer = response.getWriter()

        try {
            out = new FileOutputStream(new File(path + File.separator + fileName));
            filecontent = filePart.getInputStream();

            int read = 0;
            final byte[] bytes = new byte[1024];

            while ((read = filecontent.read(bytes)) != -1) {
                out.write(bytes, 0, read);
            }
            response.sendRedirect("SucessfulUploadServlet");
        } catch (FileNotFoundException fne) {
            writer.println("You either did not specify a file to upload or are trying to upload a file to a protected or nonexistent location.");
            writer.println("<br/> ERROR: " + fne.getMessage());
        } finally {
            if (out != null)
                out.close();

            if (filecontent != null)
                filecontent.close();
            if (writer != null)
                writer.close();
        }
    }

    private String retrieveFileName(final Part part) {
        for (String content : part.getHeader("content-disposition").split(";")) {
            if (content.trim().startsWith("filename")) {
                return content.substring(content.indexOf('=') + 1).trim().replace("\"", "");
            }
        }
        return null;
    }
}