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What JDK switcher is

This is a yet another Ubuntu/Debian-specific script that switches between multiple JDK versions (including those that may not have been installed via apt).

It is meant to be used in the travis-ci.org CI environment but may be useful in other environments, too.

Usage

Install one or more JDKs that register themselves with the update-java-alternatives tools by installing a .jinfo file under /usr/lib/jvm.

Then source jdk_switcher.sh in the repository root and use the jdk_switcher function it two arguments, a command and the JDK to use:

. ./jdk_switcher.sh

jdk_switcher  use openjdk7

jdk_switcher home oraclejdk7

jdk_switcher home ibmjdk8

Commands

  • use: switches active JDK (updates PATH alternatives and exports JAVA_HOME)
  • home: prints JAVA_HOME value for the specified JDK. Does not change anything in the environment.

JDK aliases

Supported aliases are:

  • oraclejdk8
  • oraclejdk7 or jdk7 or default
  • openjdk7
  • openjdk6 or jdk6
  • ibmjava8 or ibmjdk8

Sun JDK 6 will be EOL in November 2012 and is not supported. Ubuntu 12.04 and next Fedora release both will use OpenJDK 7 by default. Time to upgrade, JDK 7 is backwards compatible and packed with improvements.

How does it work?

The switcher uses update-java-alternatives (see also this intro) under the hood to update /etc/alternatives/* symlinks for java, javac, javap and other JDK tools. As such, the switcher itself primary handles aliasing of JDKs (update-java-alternatives aliases are too hard to remember) and updating JAVA_HOME value.

JAVA_HOME changes is the reason why jdk_switcher is implemented as a function.

Why was this tool necessary?

JAVA_HOME updates is the key reason for it to exist: update-java-alternatives and related Debian tools in general do a great job of managing alternatives but won't touch or even define JAVA_HOME. Even though most JVM ecosystem tools (from Leiningen to Elastic Search, HBase and Cassandra) will try hard to detect JAVA_HOME value but unfortunately, Maven 3 does it in a way that is heavily biased towards OpenJDK 6.

For travis-ci.org to support multiple JDKs for Clojure, Groovy, Java, Scala and JRuby, it is crucially important that all the tools we provision will use the JDK version specified for a build. We cannot let Maven always use OpenJDK 6.

License & Copyright

MIT LICENSE

Copyright (c) 2012-2016 Michael S. Klishin and Travis CI Development Team

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.