spring boot - KeyCloak Server Caused by: java.lang.ClassNotFoundException: java.security.acl.Group

Question

I'm running a KeyCloak server to authenticate users who would like to gain access to a Spring Boot/Spring Web REST API. However, an error occurs while trying to authenticate.

The following works:

• When I access http://localhost:8080/path/to/restapi
• I get presented with a login screen as expected: -- KeyCloak Login Screen
• When I click login the following error occurs on the redirect from within my browser:

Whitelabel Error Page This application has no explicit mapping for /error, so you are seeing this as a fallback.

This is the error that's printed to the Spring Boot console:

Caused by: java.lang.ClassNotFoundException: java.security.acl.Group
  at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:602) ~[na:na]
  at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:178) ~[na:na]
  at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:522) ~[na:na]
  ... 33 common frames omitted

The KeyCloak server shows that the session is active for the user to the application. However, the authenication process is never completed due to the above missing class.

Answer 1

After some research I found the answer to my problem.

The problem is that java.security.acl.Group is being deprecated since JRE 9 and marked for removal in future versions.

java.security.acl.Group is being replaced by java.security.Policy

I was running my Spring-Boot application on JRE 14 in which this class appeared to be no longer available.

So once I changed my Spring-boot application (which hosts the REST-API) to use JRE 11 the error went away.

Note: The pom.xml Java version attibute <java.version>11</java.version> needed to change as well as the JDK in the build path in Eclipse (which is the IDE I'm using) JDK Buildpath