Java5 min read

Approaching Java and JDK upgrades safely

A JDK upgrade should be ordinary maintenance. Here’s how to stop it becoming an event.

The runtime reaches further than the code

A new JDK can uncover assumptions in libraries, build plugins, container images and production flags. A clean compile is encouraging; it is not proof that the service is ready.

Build confidence one step at a time

Update the tooling, compile cleanly, run tests that represent real behaviour, then watch the service in a production-like environment. Keep unrelated refactoring out of the upgrade.

Check which framework versions support the JDK
Look for removed flags and modules
Exercise startup and graceful shutdown
Compare memory, latency and CPU under load

Make the target JDK explicit in Mavenxml

<properties>
  <maven.compiler.release>21</maven.compiler.release>
</properties>

<plugin>
  <artifactId>maven-enforcer-plugin</artifactId>
  <!-- fail early when CI uses the wrong JDK -->
</plugin>