Re: Links and file security in java servlets

Simon Brooke <>
Tue, 07 Nov 2006 09:56:08 +0000
in message <>, jonesy
('3" <') wrote:

I am using java servlets in a website, and I want to have a page that
displays links to files stored in a location on the server (separate to
public_html for security reasons).

You appreciate, I hope, that this is much /less/ secure, not more secure,
than requiring files which can be served to come only from specified

You can certainly use servlets to send any file which the account the
servlet engine runs as has permission to read, but it's a very dodgy thing
to do and potentially opens your system security right up. Are you
convinced that some hostile person cannot use your servlet to get
at /etc/shadow, for example?

The code I have currently works when just calling one file from one
servlet, but I need a page with a varying number of reports to be
displayed as links. The file names for each of these links is
retrieved from a database. The problem I have is that the global
variable, "project.file", only stores the last row in database's value,
not an individual value (file name) for each link. So every link
displayed on the page links to the same document, even though they are
labelled differently.

The following would work. I really, strongly recommend you don't do this.



import javax.servlet.*;
import javax.servlet.http.*;

 * A really dodgy way of sending files to the client
 * @author $author$
 * @version $Revision$
public class DontDoThis extends HttpServlet
    //~ Methods -------------------------------------------------------

     * Specialisation: schlurp any specified local file out onto the output
     * stream
     * @param req the request
     * @param res the response
     * @throws ServletException probably doesn't
     * @throws IOException if the file can't be found or can't be read
    protected void doGet( HttpServletRequest req, HttpServletResponse res )
        throws ServletException, IOException
        ServletOutputStream out = res.getOutputStream( );
        String fileName = req.getParameter( "filename" );
        res.setContentType( "text/plain" );

        if ( fileName != null )
                BufferedReader buffy =
                    new BufferedReader( new InputStreamReader(
                          new FileInputStream( new File( fileName ) ) ) );

                for ( String line = buffy.readLine( ); line != null;
                            line = buffy.readLine( ) )
                    out.println( line );
            catch ( FileNotFoundException e)
                res.setStatus( HttpServletResponse.SC_NOT_FOUND);
                out.println( "ERROR: file " + fileName + " not found");
            catch ( IOException e)
                res.setStatus( HttpServletResponse.SC_FORBIDDEN);
                out.println( "ERROR: " + e.getLocalizedMessage());
            res.setStatus( HttpServletResponse.SC_NOT_ACCEPTABLE);
            out.println( "ERROR: No value for filename specified");

Any ideas would be greatly appreciated.

Why do you not simply put the files to be accessed into a directory which
is within your webserver's document root, and use mod_autoindex
to generate an automatic index of that directory? Reinventing perfectly
good wheels is rarely sensible and even more rarely secure.

-- (Simon Brooke)

        ;; how did we conclude that a fucking cartoon mouse is deserving
        ;; of 90+ years of protection, but a cure for cancer, only 14?
                -- user 'Tackhead', in /. discussion of copyright law, 22/05/02

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