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From "Niall Pemberton (JIRA)" <j...@apache.org>
Subject [jira] Created: (IO-132) File Listener/Monitor
Date Sat, 20 Oct 2007 06:39:50 GMT
File Listener/Monitor
---------------------

                 Key: IO-132
                 URL: https://issues.apache.org/jira/browse/IO-132
             Project: Commons IO
          Issue Type: New Feature
            Reporter: Niall Pemberton
            Assignee: Niall Pemberton
             Fix For: 1.4
         Attachments: FileListener.java, FileMonitor.java, FileObserver.java

Commons JCI has a "fam" (file alteration monitor) module[1] which provides a listener for
file and directory create/change/delete events. I have done some work refactoring the JCI
implementation and propose adding to to Commons IO. There is already an existing request/propsal
to add similar functionality in IO-79 from Jim Harrington (which includes code).

There are IMO two main differences (IMO improvements) in this implementation over exsiting
JCI fam module:

1) It uses a matching array technique to compare previous and current directory contents which
minimizes object creation
2) FileFilters can be specified to monitor only portions of the file system, ignoring files/directories
of no interest. This is more efficient and reduces the amount of noise from un-wanted file/directory
events

>From a quick look at IO-79, the above also applies to that proposal. Additionally IMO
the solution in IO-79 would benefit from been broken out from the two DirectoryPoller and
FilePoller artifacts.

There are also some changes to the API specified in JCI's fam:
1) FileObserver (FilesystemAlterationObserver in fam) has additional init() and destroy()
methods
2) FileMonitor (FilesystemAlterationMonitor in fam) has addObserver/removeObserver methods
rather than addListener/removeListener methods. The issue (IMO) with fam is that the monitor
is fixed to the FilesystemAlterationObserverImpl implementation, rather than any FilesystemAlterationObserver
implementation. Also the ability to specify file filters means that there is a need to be
able to add more than one observer for the same root directory.

[1] http://svn.apache.org/repos/asf/commons/proper/jci/trunk/fam/

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