OSGi Community Event 2018 Presentation by Udo Hafermann (Software AG) Abstract: The Java Platform Module System delegates the job of selecting a consistent pool of modules to an external party. The OSGi Resolver happens to be a tool for selecting a consistent set of resources. Any resources. Even JPMS modules. All we need to do is encode their dependencies properly. An interesting consequence of this is that now JPMS modules can also be selected as dependencies to other kinds of resources. Even OSGi bundles… Ever since JPMS was introduced we have been enticed by the promise of building runtimes to match our OSGi applications. In this talk we will demonstrate a way to achieve this with the help of RFP-190.

1. © 2018 Software AG. All rights reserved.
Udo Hafermann
Todor Boev
MELD OSGI BUNDLES WITH
JAVA MODULES
OSGI RFP 190

2. 2 |
MOTIVATION
Example: My bundle requires AWT—what is the minimum Java module set?
© 2018 Software AG. All rights reserved. For internal use only

3. 3 |
OVERVIEW
This talk presents RFP 190: Resource Encoding of Java Modules
1. Application Domain and Problem Statement
2. Use Cases
3. Requirements
4. Proof of Concept
5. Open Ends
© 2018 Software AG. All rights reserved. For internal use only

4. 4 |
PROBLEM STATEMENT
• We want self-contained Java applications with minimal footprint
• For OSGi, we can resolve the set of required bundles
• But JRE can easily dominate the overall size
• With JPMS, we can strip down to the modules required
• How to determine which ones are required?
• R7 provides the flat list of all boot layer packages
• Removing modules from the boot layer is a trial and error process
• We need the modules as such to be visible to tools and runtime
© 2018 Software AG. All rights reserved. For internal use only

5. 5 |
USE CASES
• Build a compact Docker image
• Build a self-contained, no-installation tool
• Analyze JRE footprint, bundle by bundle
• Introspect JRE at runtime
• Create hybrid app of OSGi bundles and JPMS modules
© 2018 Software AG. All rights reserved. For internal use only

6. 6 |
GENERAL REQUIREMENTS
• Resolver can still be used to build consistent set of modules and bundles
– Should not require a new tool or component
• Bundles are not forced to explicitly reference modules
– Just as we don’t want bundles to explicitly reference bundles
• A bundle may function as a module
– OSGi framework as a special case
• Includes third-party modules
• Best-effort JPMS validation
– Rejects duplicate and (optionally) conflicting and cyclic modules
© 2018 Software AG. All rights reserved. For internal use only

7. 7 |
RESOLVING DEPENDENCIES
• Module identity and version
• Bundle package imports to module exports
• Modules to modules
• (Optional) Module services as resources
• (Optional) Requirements to module services
© 2018 Software AG. All rights reserved. For internal use only

8. 8 |
ENHANCING METADATA
• Add version range requirements for modules
• Use bundle annotations for additional JPMS module dependencies
• Replace org.osgi.framework.system.packages with module resource
representations
© 2018 Software AG. All rights reserved. For internal use only

9. 9 |
PROOF OF CONCEPT
• Modeling
– Module as special kind of bundle
– Require module as require-bundle
– Module exports as export-package
– Module provides as service-loader capability
– Module uses as service-loader requirement
• Extracts of actual metadata
• Run resolver on “awt” example
© 2018 Software AG. All rights reserved. For internal use only

10. 10 |
MODULE METADATA
© 2018 Software AG. All rights reserved. For internal use only
java.desktop
osgi.identity
osgi.identity=java.desktop
type=java-module
singleton=true
version=10.0.2
osgi.wiring.bundle
filter:=(&(osgi.wiring.bundle=java.base)(bundle-version=10.0.2)(java-module=true))
resolution:=mandatory
osgi.wiring.bundle
filter:=(&(osgi.wiring.bundle=java.prefs)(bundle-version=10.0.2)(java-module=true))
visibility:=reexport
resolution:=mandatory osgi.serviceloader
filter:=(&(osgi.serviceloader=javax.imageio.spi.ImageOutputStreamSpi)(version>=0.0.0))
resolution:=optional
cardinality:=multiple ...
...
osgi.wiring.package
osgi.wiring.package=java.awt.color
bundle-symbolic-name=java.desktop
bundle-version=10.0.2
version=0.0.0
osgi.wiring.package
osgi.wiring.package=javax.swing
bundle-symbolic-name=java.desktop
bundle-version=10.0.2
version=0.0.0
osgi.serviceloader
osgi.serviceloader=javax.sound.midi.spi.MidiDeviceProvider
version=0.0.0
...
...
Provides
Requires
osgi.wiring.bundle
osgi.wiring.bundle=java.desktop
java-module=true
bundle-version=10.0.2

11. 11 |
DEMO TEST
• org.example.awtclient 1.0.0
• osgi.wiring.package; filter:=(&(osgi.wiring.package=java.awt)(version>=0.0.0))
© 2018 Software AG. All rights reserved.

12. 12 |
THANK YOU
• Feedback welcome on https://github.com/osgi/design/blob/master/rfps/rfp-0190-
Resource%20encoding%20for%20Java%20Modules.odt
© 2018 Software AG. All rights reserved. For internal use only

13. 13 | © 2018 Software AG. All rights reserved.