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11.2. Class Sharing

Private class space
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By default, a FAB adds each Maven dependency to its private class space at run time (except for dependencies having Maven group ID org.apache.camel, org.apache.activemq, or org.apache.cxf, which are shared by default). This is a safe approach to deploying dependencies, because it reduces the risk of version inconsistencies. But it is also an expensive approach, in terms of resources, because it forces the JVM to maintain a dedicated copy of each dependency in memory, just for this FAB.

Shared class space
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You can make a FAB more economical by opting to share some of its dependencies with other applications in the container. There are two approaches you can use:

Specify shared dependencies using provided scope
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To share a dependency (and its transitive dependencies), declare a dependency with the provided scope in your project's pom.xml file. For example: 
<dependency>
  <groupId>org.acme.foo</groupId>
  <artifactId>foo-core</artifactId>
  <version>${foo-version}</version>
 <scope>provided</scope>
</dependency>
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This is analogous to the approach you would use when building a WAR with Maven, in order to avoid including libraries like the servlet API or the JSP API.

Specify shared dependencies using Manifest header
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You can also configure class sharing by setting the FAB-Provided-Dependency: manifest header. For example, to share all artifacts with the org.acme.foo Maven group ID: 
FAB-Provided-Dependency: org.acme.foo:* org.apache.camel:* org.apache.cxf:* org.apache.activemq:*
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For full details of how to use this approach, see the section called “Sharing dependencies” and the section called “How to set JAR manifest headers”.
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