It would be useful to setup system pointing in the official docker image:

update-alternatives --install "/usr/bin/java" "java" "/opt/ibm/java/jre/bin/java" 1;
update-alternatives --set java /opt/ibm/java/jre/bin/java;

In this way we get thi setup:

root@52b1a259c5a0:/# update-alternatives --display java
java - manual mode
link best version is /opt/ibm/java/jre/bin/java
link currently points to /opt/ibm/java/jre/bin/java
link java is /usr/bin/java
/opt/ibm/java/jre/bin/java - priority 1