Explanation

An XWiki version can require a newer Java version than the one you are running — Java 17 since XWiki 16.0.0, and Java 21 since XWiki 18.0.0. When the servlet container is still started with the previous Java, XWiki does not report a requirement error: the container only says that the web application failed.

Context [/xwiki] startup failed due to previous errors

Cause

The servlet container runs its own JVM, chosen independently of the system default, so upgrading XWiki does not change it and installing a newer JDK does not necessarily change it either. Tomcat reports the version it uses shortly after starting:

[info] JVM Version:           11.0.21+9-post-Ubuntu-0ubuntu122.04

The leading number is the Java version — 11 here, where XWiki 18 needs 21. Two things commonly pin it: a JAVA_HOME hard-wired in the container's configuration file, such as /etc/default/tomcat10, and, on Debian-based distributions, the default-java symbolic link that apt does not always repoint when a newer JDK is installed.

Solution

1. Read the JVM version the container reports in its log, and compare it with the Java version XWiki requires.
2. Check the container's configuration file for a JAVA_HOME setting, and point it at the required JDK.
3. Check the default-java link when the configuration sets no JAVA_HOME:

   ls -l /usr/lib/jvm/

4. Repoint that link at the required JDK when it still resolves to the old one:

   cd /usr/lib/jvm
   sudo rm default-java
   sudo ln -s java-21-openjdk-amd64 default-java

5. Restart the servlet container, and confirm that the JVM version it now reports is the required one.

FAQ

Does XWiki run on a newer Java than the one it requires?

Yes, within the versions the Java version XWiki requires lists as supported for your XWiki version — a version newer than those is not tested and may fail.

Are extra JVM options needed?

Yes, since Java 17 XWiki needs a set of add-opens switches, listed on the Java Support Strategy page. The Debian packages and the standalone distribution set them for you.

Related

• Java Support Strategy.
• Configure a Servlet Container.