Share Utils class between OSGi

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Giacomo Petillo

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Apr 14, 2021, 2:06:22 PMApr 14
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Hi all,
do you have an example of how to share a (utils) class between various OSGi plugins?

I suppose that I must create a fragment OSGi project in which I develop all the Util classes, it's right? If so, how can I add this class as an external dependency?

Thank you,
G.

Nathan Keiter

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Apr 14, 2021, 2:33:28 PMApr 14
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There's not really a good way to share classes between OSGI plugins. I'd recommend against it.


You could either combine all of your functionality into a single plugin or have a copy of the util class package in each plugin (my approach.)


If the util classes are rather stable you could use a static plugin, but if you are constantly updating them that's not ideal.


Perhaps another option would be to expose your util functions as REST endpoints then send a localhost request to the endpoint, but that would only work with simple data-in/data-out functions. This would only work in limited cases.


Typically you want your OSGI plugins to work independently out of the box as a stand-alone program. Adding dependencies to other plugins will get messy.

Nathan I. Keiter | Lead Network Applications Programmer | I.D.E.A Council Member
Gettysburg College | Information Technology | DataSystems
Campus Box 2453 | 300 North Washington Street | Gettysburg, PA 17325
Phone: 717.337.6993
https://www.gettysburg.edu<https://www.gettysburg.edu/>
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Subject: [dotcms] Share Utils class between OSGi

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Falzone, Chris

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Apr 14, 2021, 3:28:55 PMApr 14
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Yeah, as Nathan said it's not really best practice.  OSGI Plugins are meant to stand on their own.  But if you're set on going that route -- you don't need a fragment, you just need to expose (export) the package from the supplier and import it in the manifest of the consumer.  Fragments only purpose is to do that sort of thing, so it is a better use case.  For example if you have dependencies that are used in multiple OSGI Plugins you can expose them in a fragment and then have each one import the same versions of the dependency.  

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Giacomo Petillo

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Apr 15, 2021, 4:47:27 AMApr 15
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Thanks Nathan and Chris,
with your answers I have a clear idea of ​​the right way to develop an OSGi plugin: each plugin must be separate from the others.
In another scenario it's not the best, but in an OSGi environment it's the right choice.

Nathan Keiter

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Apr 15, 2021, 9:45:50 AMApr 15
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Giacomo,


Sounds like you got this! I just wanted to add one more comment.


One complicating factor (at least historically) is that you have no control of the start/deploy order of OSGI plugins.

* I have a 2 node cluster with 33 OSGI plugins on each node.
* They each have the same plugins, originally uploaded in the same order on both nodes.
* If a plugin is updated, I update it at the same time on both nodes.

However, when the dotCMS system restarts or the OSGI framework restarts, they DO NOT load the OSGI plugins in the same order.

Nathan I. Keiter | Lead Network Applications Programmer | I.D.E.A Council Member
Gettysburg College | Information Technology | DataSystems
Campus Box 2453 | 300 North Washington Street | Gettysburg, PA 17325
Phone: 717.337.6993
https://www.gettysburg.edu<https://www.gettysburg.edu/>
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From: dot...@googlegroups.com <dot...@googlegroups.com> on behalf of Giacomo Petillo <giacomo...@gmail.com>
Sent: Thursday, April 15, 2021 4:47 AM
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Subject: Re: [dotcms] Share Utils class between OSGi

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Thanks Nathan and Chris,
with your answers I have a clear idea of ​​the right way to develop an OSGi plugin: each plugin must be separate from the others.
In another scenario it's not the best, but in an OSGi environment it's the right choice.

Il giorno mercoledì 14 aprile 2021 alle 21:28:55 UTC+2 Chris Falzone ha scritto:
Yeah, as Nathan said it's not really best practice. OSGI Plugins are meant to stand on their own. But if you're set on going that route -- you don't need a fragment, you just need to expose (export) the package from the supplier and import it in the manifest of the consumer. Fragments only purpose is to do that sort of thing, so it is a better use case. For example if you have dependencies that are used in multiple OSGI Plugins you can expose them in a fragment and then have each one import the same versions of the dependency.

On Wed, Apr 14, 2021 at 2:33 PM 'Nathan Keiter' via dotCMS User Group <dot...@googlegroups.com> wrote:
There's not really a good way to share classes between OSGI plugins. I'd recommend against it.


You could either combine all of your functionality into a single plugin or have a copy of the util class package in each plugin (my approach.)


If the util classes are rather stable you could use a static plugin, but if you are constantly updating them that's not ideal.


Perhaps another option would be to expose your util functions as REST endpoints then send a localhost request to the endpoint, but that would only work with simple data-in/data-out functions. This would only work in limited cases.


Typically you want your OSGI plugins to work independently out of the box as a stand-alone program. Adding dependencies to other plugins will get messy.

Nathan I. Keiter | Lead Network Applications Programmer | I.D.E.A Council Member
Gettysburg College | Information Technology | DataSystems
Campus Box 2453 | 300 North Washington Street | Gettysburg, PA 17325
Phone: 717.337.6993<tel:(717)%20337-6993>
https://www.gettysburg.edu<https://linkprotect.cudasvc.com/url?a=https%3a%2f%2fwww.gettysburg.edu&c=E,1,ev1iOSQrtWBAriCFD64x9e8ByauSf6N9g_qPniz7b8OlUNN5fZS-53LENPDCegy4t_3Nt3f1khJllDADH2oQ3w1JMMQND3-D34iUEyVikVZieHJ8J3o7sng,&typo=1><https://www.gettysburg.edu/<https://linkprotect.cudasvc.com/url?a=https%3a%2f%2fwww.gettysburg.edu%2f&c=E,1,XnfTV9w8qM6gczH1WGbpb2mr6qdar1Bwv3PrqF4uVS89DdmG7b1rl0sb4hoG85OJN0OCxZ8uHakRZcOzYx9_CsRVVuba16fMDwD4PpaKdA,,&typo=1>>
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Sent: Wednesday, April 14, 2021 2:06 PM
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Subject: [dotcms] Share Utils class between OSGi

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Hi all,
do you have an example of how to share a (utils) class between various OSGi plugins?

I suppose that I must create a fragment OSGi project in which I develop all the Util classes, it's right? If so, how can I add this class as an external dependency?

Thank you,
G.

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jonathan...@dotcms.com

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Apr 15, 2021, 3:38:50 PMApr 15
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Hi Giacomo

I think you have two choices:

1) create an artifact and use them as a dependency and include as any other dependency in your plugin jar.
2) create a plugin that exposes an OSGI service into the OSGI context and get the reference, we used to have an example here


it shows how to expose a service from one plugin to another
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