Asaf, hello.
Good question and I don't know of any best practices. Others here may.
With the default security policy (running without "-security") I have not
attempted to write data from a web application, excluding of course
activities such as log messages or writing to sockets connected to a
database. So my short answer is: you'll just have to try writing files to
see what happens.
Given that, you cannot or do not want to be in the business of attempting to
modify the war file that held the original configuration. Obvious enough,
but probably needs to be said. You also want to consider a saved-config
file location in the file system that does not get overwritten when new war
files are deployed, meaning someplace above WEB-INF/ (I believe that is
possible).
Wish I could help more - I just don't know first hand any more to tell. I'd
start with
FileOutputStream fos = new FileOutputStream("configfile");
fos.write("bytes".getBytes());
fos.close();
and see what happens.
Mark
On 5/17/06, Asaf Lahav <[EMAIL PROTECTED]> wrote:
Hi Mark,
Is there a best practice for also writing/updating configuration file from
within the application?
Asaf Lahav
VP R&D, Prima Grid LTD.
Cellular: 972-54-4717955
Phone: 972-3-6540255
Fax: 972-3-6540254
-----Original Message-----
From: Mark Petrovic [mailto:[EMAIL PROTECTED]
Sent: Wednesday, May 17, 2006 6:02 AM
To: Tomcat Users List
Subject: Application configuration: how to read files from a web
application
A few people in the last few days on the Tomcat Users have essentially
asked: How do I read a file from disk from within my web application,
and furthermore, how do I declaratively configure the name of that file
so as to keep its path out of my code?
It's a common question, and there is a good solution that applies to
any Java application, not just a web application running in a container.
Here's the frequently used scheme: bundle the file of interest in your
appplication's war file, and from within your application, read
its contents as a resource.
Assume the application's context is named myapp, the file of interest is
thisfile.dat, and that you can arrange for the file to be placed in
your application's WEB-INF/classes directory. When the application is
unbundled by Tomcat, you should see the file in a directory listing
$ cd $CATALINA_HOME
$ ls webapps/myapp/WEB-INF/classes/thisfile.dat
webapps/myapp/WEB-INF/classes/thisfile.dat
while this is clearly Unix-like syntax, the same ideas apply to Windows.
What have we done so far? Strategically place the file along the
application's classpath. This is essential to the scheme: the file
must be along the application's classpath - and nowhere else. This is
probably worth a close read
Class Loader HOW-TO:
http://tomcat.apache.org/tomcat-5.5-doc/class-loader-howto.html
Futhermore, to declaratively configure your application, you'd like to put
this file path in your application configuration, which keeps
it hardcoded out of your code. In other words, in the application's
web.xmlfile.
So among other application configuration, you put this in your web.xml
<servlet>
<init-param>
<param-name>thefile</param-name>
<param-value>/thisfile.dat</param-value>
</init-param>
</servlet>
Finally, somewhere in your servlet, you set about retrieving the file
contents as follows:
String thefile = this.getInitParameter("thefile");
InputStream is = this.getClass().getResourceAsStream(thefile);
That's all there is to it. Of course, all of this assumes you have a
method
of using an InputStream to parse or process the file, but that is
generally
a good assumption.
--
Mark
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