In java EE, which jars should I put in the library dir?

Question

I have a Java EE project. The project is built using maven into an .ear archive. There is a library jar containing a JPA 2 persistence unit, which is located in the library

Answer 1

I won't comment on the configuration of Maven, but merely where libraries should go.

There're two main mechanisms to share libraries amongst an EAR's modules - Bundled Libraries (described in EE.8.2.1 in the Java EE 6 specification) and Installed Libraries (EE.8.2.2).

Installed Libraries are installed separately from an EAR and therefore are shared amongst many EARs on an application server.

Bundled Libraries may be installed in lib (the default library directory), a directory specified by the library-directory element of an EAR's deployment descriptor and/or in any directory to be referenced with the Class-Path manifest header of a module (or a jar referenced by a module that in turn defines a transitive library).

My understanding of the Java EE 6 spec is that Class-Path can reference any library anywhere in an EAR, but the content of the jar becomes then a non-Java EE module. It means that persistence.xml is not considered upon deployment and potential persistence contexts defined in the file won't take effect at runtime.

In your case, persistence-unit.jar seems to contain persistence unit configurations and to make them available to the other modules it should be placed in the lib directory. The other two jars - shiro-core.jar and slf4j-api.jar - can be anywhere in the EAR (including the lib directory for a simple deployment - no need to have Class-Path element in any of the referencing libraries/modules).

Wrapping it up, to ease deployment have your libraries in the lib directory unless Class-Path is used and points to another directory. In this case, you'd rather check out whether the referencing jar file is not a Java EE jar with a persistence unit definition as it won't get deployed properly (and PUs won't be available to the modules).