java.util.ServiceConfigurationError Provider not a subtype while using OSGi bundle

Question

I'm creating a Liferay 7.1 OSGi bundle, which has some external dependencies in it. In consideration of time, we opted to embed the external JAR in our OSGi Bundle. I've managed to create a bnd file, which includes all of the ElasticSearch dependencies, and put them on the bundle classpath. I've used the source-code from github ( https://github.com/liferay/liferay-portal/blob/master/modules/apps/portal-search-elasticsearch6/portal-search-elasticsearch6-impl/build.gradle ) and the bnd.bnd file, to check what's imported.

When activating the bundle, an exception is thrown:

The activate method has thrown an exception 
java.util.ServiceConfigurationError: org.elasticsearch.common.xcontent.XContentBuilderExtension: Provider org.elasticsearch.common.xcontent.XContentElasticsearchExtension not a subtype
    at java.util.ServiceLoader.fail(ServiceLoader.java:239)
    at java.util.ServiceLoader.access$300(ServiceLoader.java:185)
    at java.util.ServiceLoader$LazyIterator.nextService(ServiceLoader.java:376)
    at java.util.ServiceLoader$LazyIterator.next(ServiceLoader.java:404)
    at java.util.ServiceLoader$1.next(ServiceLoader.java:480)
    at org.elasticsearch.common.xcontent.XContentBuilder.<clinit>(XContentBuilder.java:118)
    at org.elasticsearch.common.settings.Setting.arrayToParsableString(Setting.java:1257)

The XContentBuilderExtension is from the elasticsearch-x-content-6.5.0.jar, the XContentElasticsearchExtension class, is included in the elasticsearch-6.5.0.jar. Both are Included Resources, and have been put on the classpath.

The Activate-method initializes a TransportClient in my other jar, hence it happens on activation ;).

Edit:

I've noticed that this error does NOT occur when installing this the first time, or when the portal restarts. So it only occurs when I uninstall and reinstall the bundle. (This is functionality I really prefer to have!). Maybe a stupid thought.. But could it be that there is some 'hanging thread'? That the bundle is not correctly installed, or that the TransportClient still is alive? I'm checking this out. Any hints are welcome!

Edit 2:

I'm fearing this is an incompatibility between SPI and OSGi? I've checked: The High Level Rest Client has the same issue. (But then with another Extension). I'm going to try the Low-Level Rest Client. This should work, as there are minimal dependencies, I'm guessing. I'm still very curious on why the incompatibility is there. I'm certainly no expert on OSGi, neither on SPI. (Time to learn new stuff!)

Answer 1

You can have 2 elastic search connections inside one Java app and Liferay is by default not exposing the connection that it holds.

A way around it is to rebuild the Liferay ES connector. It's not a big deal because you don't need to change the code only the OSGi descriptor to expose more services.

I did it in one POC project and worked fine. The tricky thing is to rebuild the Liferay jar but that was explained by Pettry by his google like search blog posts. https://community.liferay.com/blogs/-/blogs/creating-a-google-like-search (it is a series but it's kind of hard to navigate in the new Liferay blogs but Google will probably help) Either way it is all nicely documented here https://github.com/peerkar/liferay-gsearch

the only thing then what needs to be done is to add org.elasticsearch.* in the bnd.bnd file in the export section. You will then be able to work with the native elastic API.

Answer 2

Seems like a case where OSGi uses your bundle to solve a dependency from another bundle, probably one that used your bundle to solve a package when the system started.

Looking at the symptoms: it does not occur when booting or restarts. Also it is not a subtype.

When OSGi uses that bundle to solve a dependency, it will keep a copy around, even when you remove it. When the bundle comes back a package that was previously used by another bundle may still be around and you can have the situation where a class used has two version of itself, from different classloaders, meaning they are not the same class and therefore, not a subtype.

Expose only the necessary to minimize the effects of this. Import only if needs importing. If you are using Liferay Gradle configuration to include the bundle inside, stop - it's a terrible way to include as it exposes a lot. If using the bnd file to include a resource and create an entry for the adicional classpath location, do not expose if not necessary. If you have several bundles using one as dependency, make sure about the version they use and if the exchange objects from the problematic class, if they do, than extra care is required.

PS: you can include attributes when exporting and/or importing in order to be more specific and avoid using packages from the wrong origin.