This week's book giveaway is in the Server-Side JavaScript and NodeJS forum.
We're giving away four copies of Micro Frontends in Action and have Michael Geers on-line!
See this thread for details.
Win a copy of Micro Frontends in Action this week in the Server-Side JavaScript and NodeJS forum!
  • Post Reply Bookmark Topic Watch Topic
  • New Topic
programming forums Java Mobile Certification Databases Caching Books Engineering Micro Controllers OS Languages Paradigms IDEs Build Tools Frameworks Application Servers Open Source This Site Careers Other all forums
this forum made possible by our volunteer staff, including ...
Marshals:
  • Campbell Ritchie
  • Ron McLeod
  • Paul Clapham
  • Bear Bibeault
  • Junilu Lacar
Sheriffs:
  • Jeanne Boyarsky
  • Tim Cooke
  • Henry Wong
Saloon Keepers:
  • Tim Moores
  • Stephan van Hulst
  • Tim Holloway
  • salvin francis
  • Frits Walraven
Bartenders:
  • Scott Selikoff
  • Piet Souris
  • Carey Brown

FileUpload and File type

 
Greenhorn
Posts: 24
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
I wrote a servlet to do file upload using the commons jar. This part is working fine and I'm able to upload files successfully to the server.

My question is How do I determine the file type of each file? Users can upload files with any extensions as long as the content is text.

Eg,

The user can upload test1.txt, test2.abc, test3.fa, if all 3 files are text-based.
On the other hand, I want to stop the upload if the file is an image file, even if the filename is image.txt.


So, is there a way to check and validate the content of the file and determining the file type without restricting the file extensions?
 
Sheriff
Posts: 3036
12
Mac IntelliJ IDE Python VI Editor Java
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
It's sometimes possible to tell the type of a file based on its content. One way is to check the magic number, though not all file types have one, and there's no guarantee there won't be conflicts (though it's statistically improbable). For example, GIF files all start with the ASCII string GIF87a or GIF89a. A text file or pure binary file might also begin with this combination, but it's unlikely. Wikipedia will give you a place to start.
 
Sheriff
Posts: 22002
107
Eclipse IDE Spring VI Editor Chrome Java Ubuntu Windows
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Except if it's a text file discussing the GIF89a format
 
A sonic boom would certainly ruin a giant souffle. But this tiny ad would protect it:
the value of filler advertising in 2020
https://coderanch.com/t/730886/filler-advertising
reply
    Bookmark Topic Watch Topic
  • New Topic