Resolving "Multiple Jar files" aka "scanned from multiple locations"

Question

I am working on a jetty service, and when starting it, I get a lot of:

SomeClass scanned from multiple locations: jar: jar1!Someclass.class, jar2!Someclass.class

So a single class is provided by two jars, and which I get on runtime is undefined, which is not good. Looking at other issues I found that tattletale can help diagnosing the problem. The report, in the Multiple Jar files section lists the same classes as jetty upon startup and which jars they were in. A subset of the conflicts are:

And looking at

mvn dependency:tree -D verbose

I get:

+- ca.uhn.hapi.fhir:hapi-fhir-jpaserver-base:jar:3.7.0:compile
|  |                   ...
|  +- org.jscience:jscience:jar:4.3.1:compile
|  |  \- org.javolution:javolution:jar:5.2.3:compile

And so it seems that my fhir-base-jpaserver-base dependency pulls jscience that pulls javolution. But jscience and javolution supply some of the same classes. No other dependency to javolution exists.

My question is then, how do I go about solving this?

I could do some stuff in pom.xml but I suppose jscience needs javolution, and might break?

Answer 1

Sounds like a bug in jscience with how they packaged their jar, might want to file an issue with them.

They should either ...

• have a proper/focused jar and dependencies.
• or a standalone uber jar with no dependencies.

Not mixing the two concepts.

Meanwhile, just use the <dependency>/<exclusions> to exclude specific transitive dependencies that are causing you duplicate classes.

Also, you might want to run any of the various duplicate class/resource checker maven plugins to find any other cases you might have present on your project.