I would like to clarify which version of Java I can use freely with GeoServer. Because from last year, Java went paying in some certain way : https://www.snowsoftware.com/int/blog/2019/03/07/can-java-still-be-free-after-january-2019. It's not very clear for me what I can use with GeoServer, and for which : JRE, JVM, JDK, SE... ?
I had to update a GeoServer 2.10 installation from JRE 1.8.0_111 to 1.8.0_241. It did the job and I saw a big gain in performances. But after that came the question about the new licensing rules of Java that I forget.
According to GeoServer, I have to use Oracle JRE or OpenJDK : https://docs.geoserver.org/latest/en/user/production/java.html#production-java
For what I understand, I cannot use anymore JRE 8 for any updates more than January 2019, but I can use OpenJDK as I want, is that right ?
Can someone make things clear please :-) It will be very appreciated.
Many thanks.
You do not need to use a JRE. A JDK will work just as well.
We cannot say whether your use-case would require an Oracle Java subscription or not. You need to read the Oracle Licensing FAQs carefully and judge for yourself1.
The criteria for judging are what you use Oracle Java for, not what you use it with. This is explained in the license and FAQs.
If "use freely" includes "use for any purpose", that includes purposes for which you would need a license.
If you want a version of Java where you won't have issues related to the Oracle Java licenses, use an OpenJDK release or a release provided by a third party.
OpenJDK is licensed under GNU GPL v2 + Classpath extension. It basically means that you are free to use OpenJDK for any purpose and even ship it as part of a larger product. The main restriction is that if you modify OpenJDK and distribute the modified version, then you cannot restrict the recipient's right to redistribute, and you must provide source code of the modified OpenJDK on request, effectively to anyone who asks.
There are also trademark restrictions on the use of terms like Java, JVM and so on, but I doubt that they will apply to you.
(But my advice is not to take my advice. Instead read the GPL and associated FAQs carefully. Some relevant links are here: https://openjdk.java.net/legal/)
1 - If that is too hard, pay a lawyer or legal expert to do the reading and advise you. It is unwise to rely on legal advice from people who are not qualified.