How to integrate an external library?

English Forum Software-Development
1

Hi,
I want to use an external jar library in a newly created bundle. Where do I have to set the according build path for the external library and what else do I need to do?

Greets,
Nils

2

Hi Nils,

in an ideal case, this external library is available via maven and built for OSGi. In that case add the dependency to the pom.xml (https://github.com/OpenEMS/openems/blob/develop/cnf/pom.xml). Bndtools will take care of downloading the jar-file. Then open bnd.bnd file, the tab Build and add the jar as an entry to the Build Path using the + symbol.

You can recognize if your jar-dependency is ready for OSGi checking if the META-INF/MANIFEST.MF file inside the jar-file. It should have an Export-Package entry.

If your library is not directly available as an OSGi jar, it might be already OSGi-ified by the apache servicemix project (https://servicemix.apache.org/).

If it is really not available as an OSGi jar, you need to write a wrapper. See https://github.com/OpenEMS/openems/tree/develop/io.openems.wrapper for examples.

If your jar-file is not available on maven, copy the jar-file to your bundle project. Then add

-includeresource: \
	@lib/filename.jar; lib:=true

-buildpath: \
    ${buildpath},\
    lib/filename.jar;version=file

to your bnd.bnd file.

The the bndtools docs for more information:

Hope it works for you.
Regards,
Stefan

3

Hi Stefan,
thank you for the response! The library I want to use is the JSON-simple library. I pasted the following entry into the pom.xml:


com.googlecode.json-simple
json-simple
1.1

I also added it into the bnd.bnd build path of the new bundle. Unfortunately it still says: Unresolved requirement: Import-Package: org.json.simple

The MANIFEST.MF of that bundle only has the entry to the corresponding api I created. Should there be another entry?
Thank you for your help!

4

Solved it:
There need to be an entry made to the EdgeApp.bndrun. Under source I added in -runbundles the following entry:
com.googlecode.json-simple;version=’[1.1.1,2.0.0)’,
Now it seems to work.

5

Great it worked for you. Just two notes:

  • Clicking the “Resolve” button in “EdgeApp.bndrun” should have generated that entry in “-runbundles” automatically.
  • OpenEMS is using JSON format in many places (e.g. for the JSON-RPC-communication between Backend, Edge and UI). I made good experiences and can recommend the GSON library by google. There is also a powerful JsonUtils class that provides a lot of helper functions.