[2019 oracle code one] dependency hell

Surviving Dependency Hell

Speakers: Robert Scholte (@rfscholte) & Ray Tsang (@saturnism)

For more blog posts, see The Oracle Code One table of contents


Identifying problem

  • Setup two dependencies with Maven and ran
  • Errors: NoSuchMethodError, NoSuchFieldError, ClassNotFoundException
  • mvn dependency:tree – lots of output
  • mvn dependency:tree -Dincludes=com.google.guava – filters by the jar suspected
  • mvn dependency:tree -Dincludes=com.google.guava -Dverbose=true – shows conflicts and reason
  • Showed IntelliJ dependency tree graph

Picking a dependency

  • Classpath – first class wins
  • Maven – nearest wins
  • Maven doesn’t understand Semver (semantic versioning)
  • Use Maven Enforcer with upper bound. This assumes library is backwards compatible
  • Guava 21+ is backward compatible

Other problems

  • Shade – Copies files to creates problems. Problem if jars relocated. Only do as last resort
  • Classloaders

Solutions

  • Explicit dependency with version you need
  • Exclude dependency when pull in transitive dependency
  • Dependency management to specify version you need. Dependency management is a lookup table. It doesn’t actually need to exist. Can have a reference to a snapshot in there.
  • When making breaking changes – use new group id or artifact id. Use new package name. This is what commons lang did. – http://jlbp.dev/JLBP-6.html
  • BOM file for multi module projects with all transitive dependencies needed. Only use for modules within the project. – http://jlbp.dev/JLBP-15.html

<and then I needed to leave to get to my session in another building and get ready>

My take

Regardless of how good this is, I needed to leave early to get to my own session in another building right after this. I’m sorry I had to leave. It was excellent. I like that I learned about http://jlbp.dev so I can do more reading later.

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