Implementation/SAS:APS Server/Download.java

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import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.io.PrintWriter;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 *
 * @author Deben
 */
@WebServlet(urlPatterns = {"/Download"})
public class Download extends HttpServlet {

    /**
     * Processes requests for both HTTP <code>GET</code> and <code>POST</code>
     * methods.
     *
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    

    // <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code.">
    /**
     * Handles the HTTP <code>GET</code> method.
     *
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String device = request.getParameter("device");
        String relativePath;
        switch(device) {
            case "android":
                relativePath = getServletContext().getRealPath("/WEB-INF/android/Access control.apk");
                break;
            case "ios":
                relativePath = getServletContext().getRealPath("/WEB-INF/");
                break;
            default:
                
                return;
        }
        // reads input file from an absolute path
        
        File downloadFile = new File(relativePath);
        FileInputStream inStream = new FileInputStream(downloadFile);
         
        // if you want to use a relative path to context root:
        
        System.out.println("relativePath = " + relativePath);
         
        // obtains ServletContext
        ServletContext context = getServletContext();
         
        // gets MIME type of the file
        String mimeType = context.getMimeType(relativePath);
        if (mimeType == null) {        
            // set to binary type if MIME mapping not found
            mimeType = "application/octet-stream";
        }
        System.out.println("MIME type: " + mimeType);
         
        // modifies response
        response.setContentType(mimeType);
        response.setContentLength((int) downloadFile.length());
         
        // forces download
        String headerKey = "Content-Disposition";
        String headerValue = String.format("attachment; filename=\"%s\"", downloadFile.getName());
        response.setHeader(headerKey, headerValue);
         
        // obtains response's output stream
        OutputStream outStream = response.getOutputStream();
         
        byte[] buffer = new byte[4096];
        int bytesRead = -1;
         
        while ((bytesRead = inStream.read(buffer)) != -1) {
            outStream.write(buffer, 0, bytesRead);
        }
         
        inStream.close();
        outStream.close();  
    }

    /**
     * Handles the HTTP <code>POST</code> method.
     *
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
    }

}