I know this title is a bit of a mouthful, but you need to get all the keywords in for Google to do its magic 😉. In the previous blog post, I mentioned that I would take another look at this topic through the lens of a programmer that uses Apache Commons CLI for command-line argument handling. In a project for work, I noticed some odd error messages claiming that a command-line option did not have a value assigned to it, although it obviously did.

A more extensive set of examples can be found in the README file on GitHub, together with the code.

The sole reason for this blog post is how unknown parameters from the view of Commons CLI can mess up the parsing. The demo application defines two required Options – one for input (“-i” or “–input”) and one for output (“-o” or “–output”). Consider this command where I also set a Spring configuration setting.

% java -jar target/external-config-commons-cli-1.0.0.jar --spring.config.additional-location=src/config/application-mac.yml -i in -o out
-> AppRunner.run() Command Line Arguments
Argument: --spring.config.additional-location=src/config/application-mac.yml
Argument: -i
Argument: in
Argument: -o
Argument: out
-> ExternalConfigProperties
Input path: /Users/mac/thecode
Output path: /Users/mac/slinger
-> Parsing Help With Apache Commons CLI
-> Parsing Arguments With Apache Commons CLI
Missing required options: i, o

Both options are clearly there. The raw output of the String… args array shows that. By default, Commons CLI complains about unknown options. I disabled that behavior by setting stopAtNonOption to true. The parameter’s name makes no sense to me because it does not stop, but I might misinterpret something.

Either way, I assume that Commons CLI expects an option and a value by default. –spring.config.additional-location=src/config/application-mac.yml is a continuous string, an option without a value – at least to Commons CLI. Then it reads -i as the value to that option, and from there, the parsing goes south. The actual options are interpreted as values now.

Note, though, that Spring still accepts the configuration setting.

How can we fix that? There are two ways to do that:

1. Add the Spring arguments at the end of the command line.
2. Use the JVM-style Spring arguments with “-D”, as alluded to in the other blog post.

Putting the argument at the end:

% java -jar target/external-config-commons-cli-1.0.0.jar -i in -o out --spring.config.additional-location=src/config/application-mac.yml
-> AppRunner.run() Command Line Arguments
Argument: -i
Argument: in
Argument: -o
Argument: out
Argument: --spring.config.additional-location=src/config/application-mac.yml
-> ExternalConfigProperties
Input path: /Users/mac/thecode
Output path: /Users/mac/slinger
-> Parsing Help With Apache Commons CLI
-> Parsing Arguments With Apache Commons CLI
Found option i with value in
Found option o with value out

Using the JVM-style:

% java -Dspring.config.additional-location=src/config/application-mac.yml -jar target/external-config-commons-cli-1.0.0.jar -i in -o out
-> AppRunner.run() Command Line Arguments
Argument: -i
Argument: in
Argument: -o
Argument: out
-> ExternalConfigProperties
Input path: /Users/mac/thecode
Output path: /Users/mac/slinger
-> Parsing Help With Apache Commons CLI
-> Parsing Arguments With Apache Commons CLI
Found option i with value in
Found option o with value out

Thank you very much for reading. I hope this was helpful.