Picocli: How to pass multiple values for same key to a Map?

[guw]

I would like to group values by key with a command

Here is what I tried:

@Option(names = {"-t"}, split = ",")
protected Map<String, List<Path>> resources;

with the command arguments: -t key=a/b/c.txt,a/b/c2.txt -t key2=d/e/f.txt -t key=a/b/c3.txt

This doesn't seem to be supported. I get java.lang.ClassCastException: java.lang.String cannot be cast to java.util.List at runtime, which indicated that picocli puts a String into the map as value even though it is of type List<String>.

[remkop]

Hi!

Yes, the split attribute serves to separate map entries, it does not operate on the map values. For example:

@Option(names = {"-t"}, split = ",")
protected Map<String, Path> resources;

This would accept input like -t key=a/b/c.txt,key2=a/b/c2.txt,key3=d/e/f.txt.

But anyway, this is not what you want.
Picocli does not support Map<String, List<Path>> out of the box, but you may be able to achieve this with a custom parameter processor.

Here is an example: https://github.com/remkop/picocli/blob/master/picocli-examples/src/main/java/picocli/examples/optionaloptionparams/OptionalOptionParamDemo.java

[remkop]

@guw Did this answer your question?

[guw]

@remkop I went with a List<String> and additional parsing within the application logic to get the data I want. I haven't tried the custom parameter processor but it looks like it would do it.

[remkop]

Makes sense.
I’ll close this ticket, feel free to raise other ones at any time.

[remkop]

Please star picocli on GitHub if you like the project. :-)