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From: Apache Wiki <wikidiffs@apache.org>
To: commons-dev@jakarta.apache.org
Date: Thu, 30 Mar 2006 19:38:05 -0000
Message-ID: <20060330193805.32244.12406@ajax.apache.org>
Subject: [Jakarta-commons Wiki] Update of "VfsCacheStrategy" by
 MarioIvankovits

Dear Wiki user,

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The following page has been changed by MarioIvankovits:
http://wiki.apache.org/jakarta-commons/VfsCacheStrategy

New page:
= VFS - CacheStragey =

One problem with libraries like vfs is that they cache some data to avoid successive access to the real file - simply to speed up things.

This cache might get stale - no it GET stale.

Currently VFS provides three strategies to workaround it:

 * manual
 * on resolve (the default)
 * on call

Note: It is not possible to use {{{VFS.getManager}}} to configure the cacheStrategy. You have to create your own static class to create it.

== manual cache strategy ==

Setup
{{{
StandardFileSystemManager fs = new StandardFileSystemManager();
fs.setCacheStrategy(CacheStrategy.MANUAL);
fs.init();
}}}

using this setup you have to use {{{fileObject.refresh()}}} to refresh your object with the filesystem

== on_resolve ==

Setup
{{{
StandardFileSystemManager fs = new StandardFileSystemManager();
fs.setCacheStrategy(CacheStrategy.ON_RESOLVE);
fs.init();
}}}

every time you call {{{fs.resolveFile()}}} the file data will be refreshed. You still can use {{{fileObject.refresh()}}} to refresh the data on demand.

== on_call ==

Setup
{{{
StandardFileSystemManager fs = new StandardFileSystemManager();
fs.setCacheStrategy(CacheStrategy.ON_CALL);
fs.init();
}}}

Every time you call a method on the resolve file object the data will be refreshed with the filesystem. This will give you the behaviour you might expect from a local file but also might be a hughe performance loss as it will greatly increase the network load.

You also can archive this cache strategy if you pack the file object in an {{{org.apache.commons.vfs.cache.OnCallRefreshFileObject}}}

{{{
FileObject fo = VFS.getManager().resolveFile("....");
OnCallRefreshFileObject foc = new OnCallRefreshFileObject(fo);
}}}

the difference to the above is, that in the first case you will always get the same file object instance and thus you can synchronize against it.

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