A simple script to launch JShell against Spring Boot packaged classpath.

The script can be useful to quickly prototype on non-development environments (like Docker containers) where environment difference matters (e.g. OS features, file system structure, network policy restrictions, etc).

0. Make sure you have Java 11+ installed on target environment

1. Copy jshellw wrapper script into destination, e.g.

$ sudo docker cp jshellw mycontainer:/microservice/jshellw

2. Make the script executable

$ sudo docker exec -w /microservice mycontainer chmod +x jshellw

3. Run the script pointing to Spring Boot JAR or WAR archive

$ sudo docker exec -it -w /microservice mycontainer ./jshellw app.jar

The output should look like:

Created temp directory '/tmp/...'. Extracting classpath content...
Extracted 191 files from the archive to '/tmp/.../BOOT-INF'.
Starting JShell with '/usr/lib/jvm/java-11-openjdk-amd64/bin/jshell --feedback verbose --class-path /tmp/.../BOOT-INF/classes:/tmp/.../BOOT-INF/lib/*'...
|  Welcome to JShell -- Version 11.0.1
|  For an introduction type: /help intro

jshell>

To run the script in Windows just execute the following instead of steps 2 and 3:

java --source 11 jshellw app.jar

To check if classpath has been composed and applied correctly, type /env and you should see something like:

jshell> /env
|     --class-path /tmp/.../BOOT-INF/classes:/tmp/.../BOOT-INF/lib/HdrHistogram-2.1.9.jar:...<other-jars>...

Now you can import any classes from your classpath and work with them in JShell just like you do in your dev environment.
For example:

jshell> import org.springframework.util.StringUtils
jshell> var cleanedPath = StringUtils.cleanPath(".\\..\\core/inst/meg.dump")
cleanedPath ==> "../core/inst/meg.dump"
|  created variable cleanedPath : String

You can even launch the application at whole by invoking it's main class, e.g.

jshell> import com.example.spring.boot.application.MainClass
jshell> MainClass.main(new String[0])

but before it make sure that current value of user.dir system property points to application's home directory (if it matters).

See this Comprehensive Guide or google for java repl.