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Posted to dev@avalon.apache.org by Anton Tagunov <at...@mail.cnt.ru> on 2003/06/04 12:06:03 UTC
MissingValidity.java is this contribution welcome? :-)
Hello, Developers!
In my application I do the following: once in a while (it's
configurable) the validity of the main configuration file and logging
configuration file is checked. If they have changed the whole
Fortress instance is reloaded ( in case this fails the old one
is still used -- but I'm not speaking about that now ).
The thing is that I want to treat a missing config file just
as a broken config file - I want it to have a validity, such
that would become -1 as soon as file is created and that would
stay +1 while the file is still missing.
For this purpose I have created MissingValidity.java
It is adapted from NOOPValidity.
It is possible to return an instance of this from
FileSource.getSourceValidity() instead of null if the
file is missing.
I'm perfectly okay with having this file in my utils,
but if the overall distribution would benefit from
incorporating this, I'm submitting the file.
WBR, Anton :-)
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package ws.atagunov.avalon.validity;
import org.apache.excalibur.source.SourceValidity;
/**
* A validation object which always returns UNKNOWN for isValid()
* and VALID for isValid( validity ) if validity is of this same type
* or -1 otherwise.
*
* This validity may be used for a missing file - it remains valid
* while the file is really missing and when a file is found,
* another kind of validity (FileValidity maybe) gets compared in
* isValid( validity ) and we switch to the normal mechanims.
* Likewise if the file is deleted, the validity switches from
* FileValidity to this one.
*
* Adapted from org.apache.excalibur.source.impl.validity.NOPValidity
* by AT.
*
* @author <a href="mailto:tagunov@motor.ru">Anton Tagunov</a>
* @author <a href="mailto:cziegeler@apache.org">Carsten Ziegeler</a>
* @version CVS $Revision: 1.5 $ $Date: 2003/01/13 13:14:12 $
*/
public final class MissingValidity
implements SourceValidity
{
public static final SourceValidity SHARED_INSTANCE = new MissingValidity();
/**
* Check if the component is still valid.
* If <code>0</code> is returned the isValid(SourceValidity) must be
* called afterwards!
* If -1 is returned, the component is not valid anymore and if +1
* is returnd, the component is valid.
*/
public int isValid()
{
return 0;
}
public int isValid( final SourceValidity newValidity )
{
if (newValidity instanceof MissingValidity)
{
return 1;
}
return -1;
}
public String toString()
{
return "MissingValidity";
}
}
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Re[2]: MissingValidity.java is this contribution welcome? :-)
Posted by Anton Tagunov <at...@mail.cnt.ru>.
Hello Leo!
AT> The thing is that I want to treat a missing config file just
AT> as a broken config file - I want it to have a validity, such
AT> that would become -1 as soon as file is created and that would
AT> stay +1 while the file is still missing.
LS> isn't this wat excalibur-monitor is for?
I beleive MissingValidity just complements the SourceValidity/Monitor
duet :-)
See how it works: currently monitor/SourceResource.java goes like
this:
public long lastModified()
{
if( null == m_validity )
{
return System.currentTimeMillis();
}
...
So, if we have a missing file the corresponding SourceObject
will always be considered invalid.
Imagine that we have the following application: as soon as
a config file changes a comples object built from this configuration
is re-constructed.
But, if the configuration file is missing, on every
PassiveMonitor.getResource() a new attempt to construct the complex
object will happen. It will fail soon, as the Source object will
fail to deliver an input stream, but on every request this will
go on and on again.
In contrast if source/impl/FileSource.java would return a MissingValidity
for a missing file the situation will be the following: on the
first request an attempt to construct the complex object will be
carried out. It will fail due to the lack of InputStream. But on the
second request the attempt _won't_ be carried out -- the file will
be considered _valid_ (although missing) -- in fact it is valid --
nothing has changed and we have already examined what we currently
have. _But_ once the file _is_ created on the next request the
Source object will be considered _invalid_ -- and it will be correct
as something has changed since the last time we have examined the
situation.
So, I beleive MissingValidity plubs super-smoothely into the
SourceValidity/Monitor framework :-)
- Anton
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Re: MissingValidity.java is this contribution welcome? :-)
Posted by Leo Simons <le...@apache.org>.
Anton Tagunov wrote:
> The thing is that I want to treat a missing config file just
> as a broken config file - I want it to have a validity, such
> that would become -1 as soon as file is created and that would
> stay +1 while the file is still missing.
isn't this wat excalibur-monitor is for?
- Leo
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