Installing maven in a docker build overrides JAVA 8 with JAVA 7(!)

Question

It appears that maven overrides Java 8 with Java 7. Consider the following Dockerfile:

FROM java:8
RUN java -version && ls -l /usr/bin/java    
RUN apt-get update -y && apt-get install maven -y
RUN java -version && ls -l /usr/bin/java    

Line two will report the java version is 1.8 but line 4 will report java version is 1.7. In both cases the /usr/bin/java symlink points to /etc/alternatives/java

Besides re-installing Java 8 (which is why I started with Java:8 in the first place), how can I undo these side-effects of installing maven when building a docker image?

Answer 1

I found a minimal-delta solution although the point about not using apt-get for maven installs is noted. Here is the solution as the code

FROM java:8

# preserve Java 8  from the maven install.
RUN mv /etc/alternatives/java /etc/alternatives/java8
RUN apt-get update -y && apt-get install maven -y

# Restore Java 8
RUN mv -f /etc/alternatives/java8 /etc/alternatives/java
RUN ls -l /usr/bin/java && java -version

Obviously, the last line is unnecessary but does confirm that the result is java 8.

Answer 2

Your problem isn't Maven, it's some dumb decision made by the person who packaged Maven into a .deb for APT. Do not use Maven from a .deb. The Apache Maven project doesn't make these, doesn't know what's in them, and does not support them very much. Download the genuine tar.gz from maven.apache.org, it will happily work with whatever version of Java you've got.