[ImageJ-devel] external plugins

Jay Warrick jay.w.warrick at gmail.com
Thu Mar 19 11:32:00 CDT 2015

Thanks, Mark. I should likely be using this Handler methodology in a few places in my software, including in this case. However, I'm still concerned about detection of the plugin given the scenario I'm thinking of. But, maybe you can help me understand. I have already been able to build my software project around the SciJava plugin framework and ImageJ's PluginService to automatically recognize the plugins that are part of my own software project. The SciJava framework does its job beautifully to automatically discover the plugins I've developed within my software. However, what about the following scenario?

Person (A) downloads the binary of my software from me (B). Person (A) also downloads the .java/.class file of a just a plugin that would work within my software from third person (C). Person (A) wants to run my binary and load/use the plugin from person (C) at runtime. How would the SciJava plugin framework know how to automatically discover this plugin? 

My recollection is that the list of plugins loaded by the PluginService are determined from a java annotation index file that is created during early in the build process. Thus, I thought that if my program is already compiled and running before I specify where this "external plugin" resides and load the class, the PluginService would be unaware of the external plugin. Am I correct? If it can detect it, then it appears I'm home free and am worrying for nothing, which would be awesome.



> On Mar 19, 2015, at 8:51 AM, Mark Hiner <hiner at wisc.edu> wrote:
> Hi Jay,
> >One of the main things I can't quite envision is how to process the annotations of an external .java file at runtime so that I can utilize that information
> You shouldn't have to do this yourself. By using the SciJava plugin framework you get discovery of all annotated plugins on your classpath, and processing/indexing of those plugins, for free.
> I'm assuming the paradigm that would match your needs is a HandlerService[1]. The service would perform some function (e.g. opening a path) and the behavior of that function would be extensible via HandlerPlugins[2] (e.g. a plugin for handling URLs, files on disk, files in a database, etc...).
> The simplest example of "service chooses a plugin appropriate for the circumstances" is the AnimalService tutorial[3]. Note that it's not actually a HandlerService but could easily be converted to one. More complex examples would be the IOService[4] or SCIFIO's FormatService[5].
> Best,
> Mark
> [1] https://github.com/scijava/scijava-common/blob/scijava-common-2.39.0/src/main/java/org/scijava/plugin/HandlerService.java <https://github.com/scijava/scijava-common/blob/scijava-common-2.39.0/src/main/java/org/scijava/plugin/HandlerService.java>
> [2] https://github.com/scijava/scijava-common/blob/scijava-common-2.39.0/src/main/java/org/scijava/plugin/HandlerPlugin.java <https://github.com/scijava/scijava-common/blob/scijava-common-2.39.0/src/main/java/org/scijava/plugin/HandlerPlugin.java>
> [3] https://github.com/imagej/imagej-tutorials/tree/00394f9f5010d1787b9bf584b6e90eed01beec0d/create-a-new-plugin-type/src/main/java <https://github.com/imagej/imagej-tutorials/tree/00394f9f5010d1787b9bf584b6e90eed01beec0d/create-a-new-plugin-type/src/main/java>
> [4] https://github.com/scijava/scijava-common/blob/scijava-common-2.39.0/src/main/java/org/scijava/io/IOService.java <https://github.com/scijava/scijava-common/blob/scijava-common-2.39.0/src/main/java/org/scijava/io/IOService.java>
> [5] https://github.com/scifio/scifio/blob/scifio-0.21.1/src/main/java/io/scif/services/FormatService.java <https://github.com/scifio/scifio/blob/scifio-0.21.1/src/main/java/io/scif/services/FormatService.java>
> On Wed, Mar 18, 2015 at 6:42 PM, Jay Warrick <jay.w.warrick at gmail.com <mailto:jay.w.warrick at gmail.com>> wrote:
> Hi All,
> I am using the scijava plugin framework, ImageJ2, and its Plugin service. I would like to allow other people to write a plugin for my software. I'm open to suggestions but I'd probably like to enable them to place their java/jar/class plugin file in a folder, and I could look into that folder to load their plugin. I'm thinking along the lines of how how old ImageJ did things. Does anyone have suggestions or example code (e.g., in FIJI somewhere) for loading/compiling such plugin files during runtime. One of the main things I can't quite envision is how to process the annotations of an external .java file at runtime so that I can utilize that information (e.g., in conjunction with the PluginService). If there is an inherent problem in what I'm hoping to do, please let me know :-) (e.g., if I am provided compiled code, I suspect I might need an annotation index to go with it if I need that information).
> I figured you guys have tackled this problem thoroughly already and thus would be a good resource. Thanks in advance!
> Regards,
> Jay
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