Implementing a simple file download servlet

Question

How should I implement simple file download servlet    The idea is that with the GET request index jsp filename file txt  the user can download for example  file txt from the file servlet and the file servlet would upload that file to user    I am able to get the file  but how can I implement file download

User · Answer

The easiest way to implement the download is that you direct users to the file location, browsers will do that for you automatically.

You can easily achieve it through:

HttpServletResponse.sendRedirect()

User · Answer

And to send a largFile byte   pdfData   getPDFData     String fileType    quot  quot    res setContentType  quot application pdf quot     httpRes setContentType  quot application  pdf quot    httpRes addHeader  quot Content-Disposition quot    quot attachment  filename IDCards pdf quot    httpRes setStatus HttpServletResponse SC OK   OutputStream out   res getOutputStream    System out println pdfData length             out write pdfData   System out println  quot sendDone quot    out flush

User · Answer

That depends  If said file is publicly available via your HTTP server or servlet container you can simply redirect to via response sendRedirect     If it s not  you ll need to manually copy it to response output stream   OutputStream out   response getOutputStream    FileInputStream in   new FileInputStream my file   byte   buffer   new byte 4096   int length  while   length   in read buffer    gt  0       out write buffer  0  length     in close    out flush      You ll need to handle the appropriate exceptions  of course

User · Answer

Assuming you have access to servlet as below  http   localhost 8080 myapp download id 7   I need to create a servlet and register it to web xml  web xml   lt servlet gt        lt servlet-name gt DownloadServlet lt  servlet-name gt        lt servlet-class gt com myapp servlet DownloadServlet lt  servlet-class gt   lt  servlet gt   lt servlet-mapping gt        lt servlet-name gt DownloadServlet lt  servlet-name gt        lt url-pattern gt  download lt  url-pattern gt   lt  servlet-mapping gt    DownloadServlet java  public class DownloadServlet extends HttpServlet         protected void doGet  HttpServletRequest request  HttpServletResponse response  throws ServletException  IOException             String id   request getParameter  id              String fileName                String fileType                   Find this file id in database to get file name  and file type              You must tell the browser the file type you are going to send             for example application pdf  text plain  text html  image jpg          response setContentType fileType                Make sure to show the download dialog          response setHeader  Content-disposition   attachment  filename yourcustomfilename pdf                 Assume file name is retrieved from database             For example D   file  test pdf           File my file   new File fileName                This should send the file to browser          OutputStream out   response getOutputStream             FileInputStream in   new FileInputStream my file            byte   buffer   new byte 4096            int length           while   length   in read buffer    gt  0               out write buffer  0  length                       in close             out flush

User · Answer

Try with Resource  File file   new File  Foo txt    try  PrintStream ps   new PrintStream file        ps println  Bar      response setContentType  application octet-stream    response setContentLength  int  file length     response setHeader   Content-Disposition            String format  attachment  filename    s     file getName       OutputStream out   response getOutputStream    try  FileInputStream in   new FileInputStream file         byte   buffer   new byte 4096       int length      while   length   in read buffer    gt  0            out write buffer  0  length           out flush

[java] Implementing a simple file download servlet

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