How to Access the inner(nested) key-value in an YAML file using snakeYaml Library

Question

I am trying to read config.yaml file using the snakeYaml library in java.

I am able to get the Module name (i.e [{ABC=true}, {PQR=false}]) in my config file. Is there a way where I can directly read the value of ABC (ie true) using the code.

I have tried to search online but they are not exactly what I am looking for. Few links that I went through mentioned below:

Load .yml file into hashmaps using snakeyaml (import junit library)

https://www.java-success.com/yaml-java-using-snakeyaml-library-tutorial/

config.yaml data:

Browser: FIREFOX
Module Name:
- ABC: Yes
- PQR: No

Below is the code that I am using

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.Reader;
import java.util.Map;
import org.yaml.snakeyaml.Yaml;

public class YAMLDemo {

    public static void main(String[] args) throws FileNotFoundException {

        Yaml yaml = new Yaml();
        Reader yamlFile = new FileReader("./config.yaml");

        Map<String , Object> yamlMaps = yaml.load(yamlFile);

        System.out.println(yamlMaps.get("Browser"));
        System.out.println(yamlMaps.get("Module Name"));
    }
}

Console Output:

FIREFOX
[{ABC=true}, {PQR=false}]

Any help is really appreciated. Thanks in advance.

Answer 1

If you step through the code with a debugger, you can see that module_name is deserialised as an ArrayList<LinkedHashMap<String, Object>>:

You just need to cast it to the correct type:

public static void main(String[] args) throws FileNotFoundException {
    Yaml yaml = new Yaml();
    Reader yamlFile = new FileReader("./config.yaml");

    Map<String , Object> yamlMaps = (Map<String, Object>) yaml.load(yamlFile);

    System.out.println(yamlMaps.get("Browser"));
    final List<Map<String, Object>> module_name = (List<Map<String, Object>>) yamlMaps.get("Module Name");
    System.out.println(module_name);
    System.out.println(module_name.get(0).get("ABC"));
    System.out.println(module_name.get(1).get("PQR"));
}

Answer 2

public class YamlParser {

    public YamlParser() {
    }

    public void parse(Map<String, Object> item, String parentKey) {
    for (Entry entry : item.entrySet()) {
        if (entry.getValue() != null && entry.getValue() instanceof Map) {
        parse((Map<String, Object>) entry.getValue(),
                (parentKey == null ? "" : parentKey + ".") + entry.getKey().toString());
        } else {
        System.out.println("map.put(\"" + (parentKey == null ? "" : parentKey + ".") + entry.getKey() + "\",\""
                + entry.getValue() + "\");");
        }
    }
    }

    public static void main(String[] args) {
    try {
        Yaml yaml = new Yaml();
        InputStream inputStream = new FileInputStream(
                "path-to-application.yml");
        Map<String, Object> obj = yaml.load(inputStream);
        YamlParser parser = new YamlParser();
        parser.parse(obj, null);
    } catch (Exception ex) {
        ex.printStackTrace();
    }
    }
}

Answer 3

@Devstr has provided you With a good description on how to figure out the data structures. Here you have an example of how you can read the values into a Properties Object:

final Properties modules = new Properties();

final List<Map<String, Object>> values = (List<Map<String, Object>>) yamlMaps.get("Module Name");

values.stream().filter(Objects::nonNull)
               .flatMap(map -> map.entrySet().stream())
               .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue))
               .forEach((key, value) -> {
                   modules.put(key, value);
               });

System.out.println(modules.get("ABC"));
System.out.println(modules.get("PQR"));