Upgrade to Java 21

Java 21 is released today. It is the next LTS release after Java 17, the Java version we use now. Per our upgrade policy, I don't think we should immediately upgrade to Java 21. But, it is good to keep track of information that we can use to decide to upgrade, in due time.

In particular, I think the following new language features would be quite nice to use:

• Record patterns: https://openjdk.org/jeps/440
• Pattern matching for switch: https://openjdk.org/jeps/441

Today, also the 2023 Jakarta EE Developer Survey Report was released. Some highlights:

• "Use of Java 17 (the LTS release of Java SE) has increased to 36% (up from 26% in 2022). Java 11 use decreased from 57% in 2022 to 50% in 2023."
• "The Jakarta EE Community is deeply interested in adopting the innovations implemented in Java SE into Jakarta EE (30%). This is a good indicator that Jakarta EE 11 release plan is on the right direction by adopting new Java SE 21 features."