Dynamically set JAVA_HOME of docker container

Question

My docker container requires JAVA_HOME to be set. I have added it to the Dockerfile as below

ENV JAVA_HOME /usr/lib/jvm/java-8-openjdk-amd64/jre

However, this is a hardcoding of the value. Is there a way I can get this value dynamically from the image itself

Solution 1

Set JAVA_HOME in docker container

Default Docker file of the official image is Dockerfile

If you still want your own image with Java home set. Add this lines to your Dockerfile

RUN apt-get update && \
    apt-get install -y openjdk-8-jdk && \
    apt-get install -y ant && \
    apt-get clean && \
    rm -rf /var/lib/apt/lists/ && \
    rm -rf /var/cache/oracle-jdk8-installer;

ENV JAVA_HOME /usr/lib/jvm/java-8-openjdk-amd64/
RUN export JAVA_HOME

Solution 2

It's possible add the JAVA_HOME in a ENV Dockerfile instruction. But if the Java package is updated you have to change the ENV JAVA_HOME in your Dockerfile.

But I found a method to set the JAVA_HOME automatically without update the Dockerfile.

RUN export JAVA_HOME="$(dirname $(dirname $(readlink -f $(which java))))"

WARNING: This is only valid if you run all the commands in the same RUN a one-liner command using the '&&' operand as Mig82 says in the comments section.

I hope this can help you.

Solution 3

The image built from a Dockerfile is forever static. Its Java location will never change unless rebuilt.

When the image is started as a container, however, anything can happen. If there's any scripts that will edit the Java location during runtime, then this script is probably also where JAVA_HOME should be updated.

If you mean that you want to dynamically build your image using an arbitrary base image with differing java location then this should probably be handled by a build script.