Spring Actuator

To enable Actuator in Spring boot application

 SpringBootApplication annotation do internal Process

The @SpringBootApplication annotation is equivalent to using @Configuration, @EnableAutoConfiguration, and @ComponentScan with their default attributes. Spring Boot enables the developer to use a single annotation instead of using multiple. But, as we know, Spring provided loosely coupled features that we can use for each annotation as per our project needs.

SpringBoot 

Spring Boot is a Spring module which provides RAD (Rapid Application Development) feature to Spring framework.

It is used to create stand alone spring based application that you can just run because it needs very little spring configuration.

Advantages of Spring Boot:-

• Create stand-alone Spring applications that can be started using java -jar.
• Embed Tomcat, Jetty or Undertow directly. You don't need to deploy WAR files.
• It provides opinionated 'starter' POMs to simplify your Maven configuration.
• It automatically configure Spring whenever possible.

 Classloader is a subsystem of JVM which is used to load class files. Whenever we run the java program, it is loaded first by the classloader. There are three built-in classloaders in Java.

1. Bootstrap ClassLoader: This is the first classloader which is the superclass of Extension classloader. It loads the rt.jar file which contains all class files of Java Standard Edition like java.lang package classes, java.net package classes, java.util package classes, java.io package classes, java.sql package classes, etc.
2. Extension ClassLoader: This is the child classloader of Bootstrap and parent classloader of System classloader. It loads the jar files located inside $JAVA_HOME/jre/lib/ext directory.
3. System/Application ClassLoader: This is the child classloader of Extension classloader. It loads the class files from the classpath. By default, the classpath is set to the current directory. You can change the classpath using "-cp" or "-classpath" switch. It is also known as Application classloader.

Intermediate Operations: 

• Process the stream elements.
• Typically transforms a stream into another stream.
• Are lazy, i.e., not executed till a terminal operation is invoked.
• Does internal iteration of all source elements.
• Any number of operations can be chained in the processing pipeline.
• Operations are applied as per the defined order.
• Intermediate operations are mostly lambda functions.

Terminal Operations:

• Kick-starts the Stream pipeline.
• used to collect the processed Stream data.

Example 

int count = Stream.of(1, 2, 3, 4, 5)

.filter(i -> i <4) // Intermediate Operation filter

.count(); // Terminal Operation count