Missing double quotes for the required field using Snake Yaml

Question

i am trying to read a Yaml template and replace certain fields in the template dynamically and create a new Yaml file. My resultant yaml file should reflect the template in all aspects including the double quotes. But I am missing double quotes for the required fields when I use snake yaml. Can anyone please suggest to resolve this issue?

Example :

My yaml template is as shown below:

version: snapshot-01
kind: sample
metadata:
  name: abc
groups:
  id: "1000B"
  category: category1

---

I am reading the above template and replacing the required fields dynamically as shown below.

 Yaml yaml = new Yaml();
 InputStream inputStream = this.getClass().getClassLoader().getResourceAsStream(yamlTemplateLocation);
 Map<String, Object>yamlMap = yaml.load(inputStream);

Now I am replacing the required fields as shown below

 yamlMap.put("version","v-1.0");
 Map<String, Object> metadata = (Map<String, Object>) yamlMap.get("metadata");
 metadata.put("name", "XYZ");

 Map<String, Object> groups = (Map<String, Object>) yamlMap.get("groups");
 groups.put("id","5000Z");
 groups.put("category","newCategory");

        DumperOptions options = new DumperOptions();
        options.setDefaultFlowStyle(DumperOptions.FlowStyle.BLOCK);
        options.setPrettyFlow(true);

        Yaml yaml = new Yaml(options);
        String output = yaml.dump(map);
        System.out.println(output);

I am expecting output as shown below

Expected Output :

version: v-1.0
kind: sample
metadata:
  name: XYZ
groups:
  id: "5000Z"
  category: newCategory

---

But I am actually getting output as below

version: v-1.0
kind: sample
metadata:
  name: XYZ
groups:
  id: 5000Z
  category: newCategory

---

My problem here is, I am missing the double quotes for "id" node in the new yaml file. When I use, options.setDefaultScalarStyle(ScalarStyle.DOUBLE_QUOTED), I am getting all fields double quoted which is not required. I need double quotes for id field only. Can anyone please advice to resolve this issue.

Thanks

Answer 1

If your input is a template, it might be better to use a templating engine. As simple example, MessageFormat would allow you to write id: "{0}" and then interpolate the actual value into it, keeping the double quotes. You could use more sophisticated templating depending on your use-case.

---

That being said, let's look at how to do it with SnakeYAML:

If you want to control how a single item is rendered as scalar, you have to define a class like this:

class QuotedString {
    public String value;

    public QuotedString(String value) {
        this.value = value;
    }
}

And then create a custom representer for it:

class MyRepresenter extends Representer {
    public MyRepresenter() {
        this.representers.put(QuotedString.class, new RepresentQuotedString());
    }

    private class RepresentQuotedString implements Represent {
        public Node representData(Object data) {
            QuotedString str = (QuotedString) data;
            return representScalar(
                    Tag.STR, str.value, DumperOptions.ScalarStyle.DOUBLE_QUOTED);
        }
    }
}

Modify your code to use the new class:

groups.put("id", new QuotedString("5000Z"));

And finally, instruct SnakeYAML to use your representer:

Yaml yaml = new Yaml(new MyRepresenter(), options);

This should do it.