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Directory sync

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©1996-2017 Roedy Green of Canadian Mind Products

Disclaimer

This essay does not describe an existing computer program, just one that should exist. This essay is about a suggested student project in Java programming. This essay gives a rough overview of how it might work. I have no source, object, specifications, file layouts or anything else useful to implementing this project. Everything I have prepared to help you is right here.

This project outline is not like the artificial, tidy little problems you are spoon-fed in school, when all the facts you need are included, nothing extraneous is mentioned, the answer is fully specified, along with hints to nudge you toward a single expected canonical solution. This project is much more like the real world of messy problems where it is up to you to fully the define the end point, or a series of ever more difficult versions of this project and research the information yourself to solve them.

Everything I have to say to help you with this project is written below. I am not prepared to help you implement it; or give you any additional materials. I have too many other projects of my own.

Though I am a programmer by profession, I don’t do people’s homework for them. That just robs them of an education.

You have my full permission to implement this project in any way you please and to keep all the profits from your endeavour.

Please do not email me about this project without reading the disclaimer above.

This is a simple project. It requires almost no user interface. The code can be cannibalised from various code posted on this website. It works like this: The source and target directories might be on the same machine or on two different machine connected on a LAN (Local Area Network). Your program makes sure the target directory is identical to the source directory doing as necessary: To copy files use FileTransfer. To traverse directory trees, use Batik. You will need to write a little JNI (Java Native Interface) to detect and set the Windows file attributes (or other platform) Use FileTimes as a base. You might be able to get around that problem by using zip files for transport which might automatically transfer the attribute bits.

There are many other directory sync programs, but they are too complicated and suffer from featuritis.

Extensions:

  1. A version of this program that does not delete any files in the target directory tree. You might call it Propagate.
  2. When the source and target are on different machines, compress the changes and send them as a single big zip. For this approach to make sense, you have a tricky problem to solve, how to spawn a task on the other computer.
  3. A version that uses FTP (File Transfer Protocol) to ensure a directory on server matches the one on the desktop.
  4. Note that the Replicator will propagate a directory tree to many machines via an HTTP (Hypertext Transfer Protocol) server.
  5. Add a GUI (Graphic User Interface) to let you define multiple directory trees.
  6. A two way sync, so that both directories end up identical. You take the more recent file on either side as the master, with a warning if the newer file is smaller. You might call this program Sync.
AllWaysync: prissy, frets over all caps files and fails when it needlessly builds intermediate temporary directories
GoodSync: free to non-profits. Overly complicated
Smart FTP project
the Replicator

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