Since Java 11 is modularized, some classes have vanished from the standard runtime environment. In order to compile CMCC, you might need some of the following additional dependencies in your project modules.

<dependency>
   <groupId>jakarta.annotation</groupId>
   <artifactId>jakarta.annotation-api</artifactId>
</dependency>
<dependency>
   <groupId>com.sun.activation</groupId>
   <artifactId>jakarta.activation</artifactId>
</dependency>
<dependency>
   <groupId>jakarta.transaction</groupId>
   <artifactId>jakarta.transaction-api</artifactId>
</dependency>
<dependency>
   <groupId>jakarta.xml.bind</groupId>
   <artifactId>jakarta.xml.bind-api</artifactId>
</dependency>
<dependency>
   <groupId>org.glassfish.jaxb</groupId>
   <artifactId>jaxb-runtime</artifactId>
</dependency>

The necessity of jaxb-runtime turns out only if you (transitively) encounter concrete jaxb-api features. You should always declare this as a runtime dependency together with the jaxb-api dependency.

The order of collections differs between Java 8 and 11.  If the order is relevant, use Lists or sort before you iterate.

With Java 11, some components need more memory, which is mainly caused by the GlassFish ORB. If your application suddenly runs out of memory with Java 11,  try with 32M additional heap memory.