A cache is a hardware or software component that stores data so future requests for that data can be served faster; the data stored in a cache might be the result of an earlier computation, or the duplicate of data stored elsewhere. A cache hit occurs when the requested data can be found in a cache, while a cache miss occurs when it cannot. Cache hits are served by reading data from the cache, which is faster than recomputing a result or reading from a slower data store. (Ref=Wikipedia)

The devtools module adds tools that can make the application development easier. This includes automatically applying sensible development-time configuration for features such as caching, auto restarting after changes etc. To include devtools support, we need to add spring-boot-devtools dependency to the build file.

YAML is a human friendly data serialization standard, which is mainly made for configuration files. YAML stands for YAML Ain't Markup Language. YAML can be used with many programming languages.

For externalized configurations, Spring Boot supports file formats such as YAML and the .properties file.

While properties file works with @PropertySource annotation, YAML does not. While we can configure more than one Spring profiles per properties file, we can have any with YAML files.

@ConfigurationProperties

EnableAutoConfiguration

1. EnableAutoConfiguration annotation attempt to guess and configure beans that you are likely to need.

2. Auto-configuration classes are usually applied based on the presence or absence of, files or libraries in your classpath, beans you have defined, and properties.  

3. Auto-configuration is always applied after user-defined beans have been registered.