Q1. What is YAML?
A1. YAML Ain’t Markup Language. It is a human friendly data serialization standard for all programming languages. A YAML file has an extension of “.yml“.

Q2. What are the 3 rules of YAML?
A2.

Rule 1: Indentation YAML uses a fixed indentation scheme to represent relationships between data layers (i.e. 2 spaces). Never use a tab.

---
YAML: YAML Ain't Markup Language

What It Is: YAML is a human friendly data serialization
  standard for all programming languages.

Projects:
  - PyYaml        # YAML 1.1, pure python and libyaml binding
  - PySyck        # YAML 1.0, syck binding
  Java:
  - JvYaml        # Java port of RbYaml
  - SnakeYAML     # Java 5 / YAML 1.1
  - YamlBeans     # To/from JavaBeans
  - JYaml         # Original Java Implementation

Rule 2: Colons & case sensitive All keys/properties are case-sensitive. (“Hello”, is not the same as “hello”) and key value pairs are separated by “:” followed by a space.

YAML: YAML is case sensitive

Keys can be nested.

first_level_dict_key:
  second_level_dict_key: value_in_second_level_dict

Rule 3: Dashes To represent lists of items, a single dash followed by a space is used. Multiple items are a part of the same list as a function of their having the same level of indentation.

 Java:
  - JvYaml        # Java port of RbYaml
  - SnakeYAML     # Java 5 / YAML 1.1
  - YamlBeans     # To/from JavaBeans
  - JYaml         # Original Java Implementation

Q3. Where will you use YAML in Java application?
A3.

1) Configuring applications: Java developers mostly deal with property (.properties), XML, and JSON files for configuring applications. YAML file can be used to configure Java applications without being too verbose as XML and being more expressive than .properties and JSON formats.

All you need is the YAML library

<dependency>
    <groupid>org.yaml</groupid>
    <artifactid>snakeyaml</artifactid>
    <version>1.11</version>
</dependency>

Java application.yml file example

#Configure a DataSource

spring:

  datasource:
    driver-class-name: com.sybase.jdbc4.jdbc.SybDataSource
    url: jdbc:sybase:Tds:mydb-host:5700/mydb
    username: user
    password: password

The properties can be accessed via Spring configs as

@Configuration
@EnableTransactionManagement
public class AppConfig {

    @Autowired
    private Environment environment;
	
	@Bean
    public DriverManagerDataSource datasource() {
    	DriverManagerDataSource ds = new DriverManagerDataSource();
    	ds.setDriverClassName(environment.getRequiredProperty("spring.datasource.driver-class-name"));
    	ds.setUrl(environment.getRequiredProperty("spring.datasource.url"));
    	ds.setUsername(environment.getRequiredProperty("spring.datasource.username"));
    	ds.setPassword(environment.getRequiredProperty("spring.datasource.password"));
    	return ds;
    }
} 

Can you spot the expressive nature of the YAML file?

2) Serialize & Deserialize Java objects: YamlBeans makes it easy to serialize and deserialize Java object graphs. YAML is a human-friendly data format. Replace XML and properties files with YAML for more expressive power.

3) Spring boot supports YAML E.g.application.yml file.

More application configuration examples

Logging

logging:
  path: ./logs/
  file: myapp
  level.com.mytutorial: DEBUG
  level.: INFO
  

Messaging

env:

  mq:
    hostname: my-mq-host
    channel: mychannel
    port: 3500
    queue.manager: JKGHJK
    environment: EN7