Preserving existing comments when parsing, modifying and dumping a YAML document

Question

Is there a library in a JVM language that allows me to parse an existing YAML document, accomplish a small modification in the file and dump it as another file such as existing comments are preserved?

Answer 1

As I understand it Jython runs on the JVM, with that you should be able to use ruamel.yaml¹:

$ python
Jython 2.7.0 (default:9987c746f838, Apr 29 2015, 02:25:11) 
[OpenJDK 64-Bit Server VM (Oracle Corporation)] on java1.7.0_111
Type "help", "copyright", "credits" or "license" for more information.
>>> import ruamel.yaml
>>> yaml = ruamel.yaml.YAML()
>>> data = yaml.load("""\
... a:
...   - elem1   # not very insteresting
...   - elem2   # more of the same
... b:
...   - 42
... c: {key: value}   # does it work?
... """)
>>> import sys
>>> yaml.dump(data, sys.stdout)
a:
- elem1     # not very insteresting
- elem2     # more of the same
b:
- 42
c: {key: value}   # does it work?
>>> exit()
$ 

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¹ _{Disclaimer: I am the author of that package.}