Java version updated on package installation

Question

I have issue with updated symlink on java after maven installation. I use simple docker file:

FROM java:8
RUN ["java", "-version"]
RUN apt-get update && apt-get install -y maven && rm -rf /var/lib/apt/lists/*
RUN ["java", "-version"]
CMD ["java", "-version"]

During build I've got next log:

Step 0 : FROM java:8
 ---> 4cd29d33e3f4
Step 1 : RUN java -version
 ---> Running in 1c528620f318
openjdk version "1.8.0_66-internal"
OpenJDK Runtime Environment (build 1.8.0_66-internal-b01)
OpenJDK 64-Bit Server VM (build 25.66-b01, mixed mode)
 ---> d25e96460a85
Removing intermediate container 1c528620f318
Step 2 : RUN apt-get update && apt-get install -y maven && rm -rf /var/lib/apt/lists/*
....installation logs....
Setting up openjdk-7-jre-headless:amd64 (7u79-2.5.6-1~deb8u1) ...
update-alternatives: using /usr/lib/jvm/java-7-openjdk-amd64/jre/bin/rmid to provide /usr/bin/rmid (rmid) in auto mode
update-alternatives: using /usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java to provide /usr/bin/java (java) in auto mode

So as you can see maven brings java 7 and update-alternatives makes it default version. So I have several questions:

1. Why maven requires java 7 while java 8 already installed? Why dependencies are not transparent?
2. Is it possible to not install java 7 and use java 8 instead?
3. If not, what is the best way to set java 8 as default? Remove java 7, configure update-alternatives or something else?

Answer 1

I think all this is distro specific.

As in: In your chosen distro (Ubuntu?) the particular maven package that you are installing has a dependency to OpenJDK 7 (and not 8).

I see two options for a Java 8 / maven setup:

• install maven from a tgz
• create your own maven package

Answer 2

I tried out your setup see

https://github.com/BITPlan/docker-stackoverflowanswers/tree/master/33324470

and by running:

./build
./run

i entered a bash to see what the situation is:

Java Version

root@940c282bd6ad:/# java -version
java version "1.7.0_79"
OpenJDK Runtime Environment (IcedTea 2.5.6) (7u79-2.5.6-1~deb8u1)
OpenJDK 64-Bit Server VM (build 24.79-b02, mixed mode)

So by default this distro uses an OpenJDK 1.7

Maven Version

root@940c282bd6ad:/# mvn -version
Apache Maven 3.0.5
Maven home: /usr/share/maven
Java version: 1.8.0_66-internal, vendor: Oracle Corporation
Java home: /usr/lib/jvm/java-8-openjdk-amd64/jre
Default locale: en, platform encoding: UTF-8
OS name: "linux", version: "4.1.10-boot2docker", arch: "amd64", family: "unix"

The maven uses Oracle Java 1.8

Now you have got multiple options

Select another default java as outlined in

https://askubuntu.com/questions/272187/setting-jdk-7-as-default

root@940c282bd6ad:/# update-alternatives --config java
There are 2 choices for the alternative java (providing /usr/bin/java).

  Selection    Path                                            Priority   Status
------------------------------------------------------------
* 0            /usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java   1071      auto mode
  1            /usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java   1071      manual mode
  2            /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java   1069      manual mode

Switch the default java version as outlined in:

https://askubuntu.com/questions/491778/switch-to-oracle-java-jdk-in-14-04