Modifying YAML in java while preserving comments

Question

How can we modify an existing YAML and preserve comments in it. Is there any Java parser which does that ? For example if i have following YAML:

#This is a test YAML
 name: abcd
 age: 23
#Test YAML ends here.

Is there a way I can edit this Yaml using a java parser and preserve the comments.

Answer 1

At least since snakeyaml 2.0 (which I'm using) it is possible to preserve comments. The only drawback seems to be that you cannot parse the YAML to a Map or some other class, because that erases the comment information. That is only stored in snakeyaml's internal Nodes.

LoaderOptions loaderOptions = new LoaderOptions();
loaderOptions.setProcessComments(true);
DumperOptions dumperOptions = new DumperOptions();
dumperOptions.setProcessComments(true);
Yaml yaml = new Yaml(new Constructor(loaderOptions), new Representer(dumperOptions), dumperOptions, loaderOptions);
Node root;
try (FileReader reader = new FileReader(yamlFile)) {
    root = yaml.compose(reader);
}
try (FileWriter writer = new FileWriter(cloneFile)) {
    yaml.serialize(root, writer);
}

The only difference I get between in- and output are different line endings (can be configured in the DumperOptions) and some of my previously empty lines will have indenting spaces.