How to read from YAML file in java?

Question

I have YAML file like this..

Product:
 ProductA:
  Suite:
    SuiteName_A:
      Environment_1: ["A","B","C"]
      Environment_2: ["X","Y","Z"]
    SuiteName_B:
      Environment_1: ["E","F","G"]
      Environment_2: ["K","L","M"]
 ProductB:
  Suite:
    SuiteName_K:
      Environment_1: ["A1","B2","C3"]
      Environment_2: ["X1","Y1","Z1"]

Edited---- I have created few classes as I read in some read article and here what i came up with..

Environment Class

    package Configuration;

import java.util.ArrayList;

public class Environment {
    private ArrayList<String> Environment_1;
    private ArrayList<String> Environment_2;

    public ArrayList<String> getEnvironment_1() {
        return Environment_1;
    }

    public void setEnvironment_1(ArrayList<String> Environment_1) {
        this.Environment_1 = Environment_1;
    }

    public ArrayList<String> getEnvironment_2() {
        return Environment_2;
    }

    public void setEnvironment_2(ArrayList<String> Environment_2) {
        this.Environment_1 = Environment_2;
    }
}

SuitName Class

    package Configuration;

import java.util.HashMap;

public class SuiteNames {
    private HashMap<String,Environment> Suite;

    public HashMap<String, Environment> getSuite() {
        return Suite;
    }

    public void setSuite(HashMap<String, Environment> suite) {
        Suite = suite;
    }
}

Product Class

    package Configuration;

import java.util.HashMap;

public class Product {
    private HashMap<String,SuiteNames> Product;

    public HashMap<String, SuiteNames> getProduct() {
        return Product;
    }

    public void setProduct(HashMap<String, SuiteNames> product) {
        this.Product = product;
    }
}

Main Class

    package Configuration;

import org.yaml.snakeyaml.Yaml;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.InputStream;

public class DbClass {

    public static void main(String[] args) throws FileNotFoundException {
        Yaml yaml = new Yaml();
        InputStream inputStream = new FileInputStream("path");
        System.out.println(inputStream);
        Product product = yaml.loadAs(inputStream,Product.class);
        System.out.println(product.getProduct());
    }
}

This gives following error:

     Exception in thread "main" Cannot create property=Product for JavaBean=Configuration.Product@4c98385c
 in 'reader', line 1, column 1:
    Product:
    ^
Unable to find property 'Product' on class: Configuration.Product
 in 'reader', line 2, column 3:
      Check-in:
      ^

    at org.yaml.snakeyaml.constructor.Constructor$ConstructMapping.constructJavaBean2ndStep(Constructor.java:270)
    at org.yaml.snakeyaml.constructor.Constructor$ConstructMapping.construct(Constructor.java:149)
    at org.yaml.snakeyaml.constructor.Constructor$ConstructYamlObject.construct(Constructor.java:309)
    at org.yaml.snakeyaml.constructor.BaseConstructor.constructObjectNoCheck(BaseConstructor.java:216)
    at org.yaml.snakeyaml.constructor.BaseConstructor.constructObject(BaseConstructor.java:205)
    at org.yaml.snakeyaml.constructor.BaseConstructor.constructDocument(BaseConstructor.java:164)
    at org.yaml.snakeyaml.constructor.BaseConstructor.getSingleData(BaseConstructor.java:148)
    at org.yaml.snakeyaml.Yaml.loadFromReader(Yaml.java:525)
    at org.yaml.snakeyaml.Yaml.loadAs(Yaml.java:519)
    at Configuration.DbClass.main(DbClass.java:17)
Caused by: org.yaml.snakeyaml.error.YAMLException: Unable to find property 'Product' on class: Configuration.Product
    at org.yaml.snakeyaml.introspector.PropertyUtils.getProperty(PropertyUtils.java:159)
    at org.yaml.snakeyaml.introspector.PropertyUtils.getProperty(PropertyUtils.java:148)
    at org.yaml.snakeyaml.constructor.Constructor$ConstructMapping.getProperty(Constructor.java:287)
    at org.yaml.snakeyaml.constructor.Constructor$ConstructMapping.constructJavaBean2ndStep(Constructor.java:208)
    ... 9 more

I want get the list of Environent names and to store this in a list. I am aware using jackson api. But I don't know how to map this data to class. I am using servlets and inside the servlet i want to have a java method to get the list of strings.

Answer 1

YAML has a list of recommended libraries for Java: SnakeYAML, YamlBeans and eo-yaml

The most widely used of these is probably SnakeYAML. Baeldung has a very easy to understand tutorial here: https://www.baeldung.com/java-snake-yaml

[Edit to address new code and output in edit by OP]:

You also have some problems with the formatting and naming conventions you used. In your yaml file [brackets] are needed around any Lists, instance variables need to be camelCase, and any Strings need to be surrounded by quotes (including String HashMap keys):

products:
  "ProductA":
    suite:
      "SuiteName_A":
        environment_1: ["A","B","C"]
        environment_2: ["X","Y","Z"]
      "SuiteName_B":
        environment_1: ["E","F","G"]
        environment_2: ["K","L","M"]
  "ProductB":
    suite:
      "SuiteName_K":
        environment_1: ["A1","B2","C3"]
        environment_2: ["X1","Y1","Z1"]

You should try to match this in your bean naming convention. Also your 2nd setter needs to set Environment_2 instead of Environment_1. Here's how your entity classes would look.

Environment

package Configuration;

import java.util.ArrayList;

public class Environment {
    private ArrayList<String> environment_1;
    private ArrayList<String> environment_2;

    public ArrayList<String> getEnvironment_1() {
        return environment_1;
    }

    public void setEnvironment_1(ArrayList<String> environment_1) {
        this.environment_1 = environment_1;
    }

    public ArrayList<String> getEnvironment_2() {
        return environment_2;
    }

    public void setEnvironment_2(ArrayList<String> environment_2) {
        this.environment_2 = environment_2;
    }
}

SuiteNames

package Configuration;

import java.util.HashMap;

public class SuiteName {
    private HashMap<String,Environment> suite;

    public HashMap<String, Environment> getSuite() {
        return suite;
    }

    public void setSuite(HashMap<String, Environment> suite) {
        suite = suite;
    }
}
package Configuration;

import java.util.HashMap;

public class Product {
    private HashMap<String, SuiteName> products;

    public HashMap<String, SuiteName> getProducts() {
        return products;
    }

    public void setProducts(HashMap<String, SuiteName> products) {
        this.products = products;
    }
}

Edit: In your main method you will probably want to use yaml.load(inputStream) to get the whole file in a HashMap. Based on your question in the comment I've added accessing the data structure.

DbClass

package Configuration;

import org.yaml.snakeyaml.Yaml;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.HashMap;

public class DbClass {

    public static void main(String[] args) throws FileNotFoundException {
        Yaml yaml = new Yaml();
        InputStream inputStream = new FileInputStream("path.yml");
        System.out.println(inputStream);

        HashMap yamlMap = yaml.load(inputStream);
        for (Object o : yamlMap.entrySet()) {
            System.out.println(o);
        }
        // Access HashMaps and ArrayList by key(s)
        HashMap products = (HashMap) yamlMap.get("products");
        HashMap product = (HashMap) products.get("ProductA");
        HashMap suite = (HashMap) product.get("suite");
        HashMap suiteName = (HashMap) suite.get("SuiteName_B");
        ArrayList environment = (ArrayList) suiteName.get("environment_1");
        System.out.println(environment);
    }
}

Answer 2

This is invalid YAML:

      Environment_1: "A","B","C"

You need to do

      Environment_1: ["A","B","C"]

Then, the setters have wrong names:

    public ArrayList<String> getEnvironment_1() {
        return Environment_1;
    }

    public void setINT(ArrayList<String> Environment_1) {
        this.Environment_1 = Environment_1;
    }

The setter must be named setEnvironment_1. This is because SnakeYAML accesses private fields via their getters & setters.

The next problem is that the names in the YAML begin with an uppercase letter. SnakeYAML uses the JavaBeans API to discover properties, and that will yield environment_1 as property name, not Environment_1. You remedy this by overriding property discovery:

final PropertyUtils uppercaseUtils = new PropertyUtils() {
    @Override
    public Property getProperty(Class<? extends Object> type, String name) throws IntrospectionException {
        return super.getProperty(name.substring(0, 1). toLowerCase() + name. substring(1));
    }
}
final Constructor c = new Constructor(Product.class);
c.setPropertyUtils(uppercaseUtils);
Yaml yaml = new Yaml(c);