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Aug 30, 2016

Docker + JShell + Bash Alias Tip


Overview

This post brings together two of my favorite things: bash aliases/functions and docker containers. To those who have not heard, Java 9 will include a new Java REPL called JShell. This is exciting in a number of ways. Newcomers to the language should find the learning curve less painful, and seasoned developers will gain a useful tool for exploring new libraries and interactive programming. JShell has already become a tool I use daily, and it has largely replaced my habit of writing disposable JUnit tests simply to explore a new library’s behavior or work out a specific function.

With some help from docker, you can easily start exploring JShell.

JShell with Docker

The following command uses the official openjdk docker hub image.

Launch JShell

 docker run --rm=true -it openjdk:9 jshell 

Bash Alias/Function Convenience

To get the most value out of your JShell experience, you will likely want to add library jars to your classpath. This can easily be accomplished using a volume mount and a small modification to our jshell command. For convenience, I have the following bash functions defined to make launching a JShell instance with a useful classpath convenient.

Adding a lib directory to the classpath
function jshell(){
 docker run --rm=true -it -v ~/utils/jshell/libs:/tmp/context openjdk:9 /usr/bin/jshell -classpath "/tmp/context/*"
}
Adding your current directory to the classpath
function jshellpwd(){
 docker run --rm=true -it -v ${PWD}:/tmp/context openjdk:9 /usr/bin/jshell -classpath "/tmp/context/*"
}