=======================
What is SpringBoot ?
=======================

=> It is java based framework to develop applications easily.

=> SpringBoot is an extension of Spring framework.

=> SpringBoot is an approach to develop spring based applications with less configurations.

=> SpringBoot 1.x version released in 2015.

=> The current version of SpringBoot is 3.x.

Note: All spring modules and spring concepts we can use in Spring Boot.

=====================================
What we can develop using SpringBoot
=====================================

1) Console based applications

2) Web based applications

3) Distributed applications (webservices)

4) Microservices

============================
Advantages with Spring Boot
============================

1) POM starters

2) Auto Configuration

3) Embedded Servers

4) Actuators

5) Rapid Application Development

==============
POM Starters
==============

=> SpringBoot simpilified maven & gradle dependencies configurations using POM Starters.

=> POM starters are nothing but maven dependencies required for the application development.

=> We have several pom starters in springboot like below

Ex: 
		a) spring-boot-starter-web
		
		b) spring-boot-starter-data-jpa
		
		c) spring-boot-starter-security
		
		d) spring-boot-starter-mail		
		
====================
Auto Configuration
====================

=> AutoConfiguration is the process of identifying configurations required for the application and provide them whenever needed.

=> SpringBoot will take care of configurations required for the application.
		
Notes: In Springboot, auto configurations will work based on POM starters we have added in the project.	

Ex : 

	web-starter ====> tomcat container will start
	
	security-starter ===> login page for security
	
	jpa-starter ===> connection pool for db communications
	
=================		
Embedded Servers
==================

=> In general, to run java web application we need to download and setup server (Ex: Tomcat).

=> If we are using springboot, we no need to setup server to run web applications because springboot will take care of servers to run our applications. i.e Embedded Servers.
		
=> SpringBoot will support 3 embedded containers

			1) tomcat (default)
			2) jetty
			3) netty


============	
Actuators	
============

=> Used to monitor and manage springboot application	

Ex : 

1) appliction health checks
2) classes loaded by application
3) heap details
4) Threads details

====================
Rapid Development	
====================

=> Springboot supports rapid application development (quickly we can develop and run applications)

=> We can build applications that we can just run immediatley.

=> We can build production grade applications using springboot.


=============
Conclusion
=============

SpringBoot = spring - xml configurations + auto configurations

=========================================
Developing First SpringBoot application
=========================================

1) Initilizr website (start.spring.io)

		-> create project
		-> download as zip file
		-> extract zip file
		-> import into IDE 

2) STS IDE (directly we can create)

=> Below is the folder structure of springboot application.

01_sb_app

	src/main/java
		- Application.java (start class)
	
	src/main/resources
		- application.properties
	
	src/test/java
	
	src/test/resources
	
	Maven Dependencies
	
	pom.xml
	
===================================
What is start class in springboot ?	
===================================

=> When we create springboot application by default one java class will be created with main () method that is called as start class of spring boot.

=> Start Class is entrypoint for springboot application execution.

------------------------------------------------------
@SpringBootApplication
public class Application {

	public static void main(String[] args) {
		
		SpringApplication.run(Application.class, args);
	}
}
------------------------------------------------------
=> In Boot start class we can see 

		@SpringBootApplication
		
		SpringApplication.run (..)
		
Note: run () method contains logic to start IOC and it returns reference of IOC.

=> spring boot will use below classes to start IOC based on starter configured in pom.xml		
		
// boot-starter
AnnotationConfigApplicationContext
		
// boot-starter-web		
AnnotationConfigServletWebServerApplicationContext

// boot-starter-webflux
AnnotationConfigReactiveWebServerApplicationContext	


===================
Component Scanning	
===================

=> The process of identifying spring bean classes available in the application is called as Component scanning.

=> Component scanning will work based on package names.

=> Ioc will scan base package and its sub packages to identify spring bean classes.

Note: The package which contains start class is called as base package.

		in.ashokit  (base package)  (will scan)
		
			- Application.java
			
		in.ashokit.dao   (will scan)
		in.ashokit.service (will scan)
		in.ashokit.util (will scan)
		
		com.oracle.secuirty (no scanning)
		
===============================================		
Can we configure more than one base package ?	
===============================================

Yes, we can do using @ComponentScan annotation at start class like below

------------------------------------------------------
@SpringBootApplication
@ComponentScan(basePackages = {"in.ashokit", "com.oracle"})
public class Application {

	public static void main(String[] args) {
		
		ConfigurableApplicationContext ctxt = 
				SpringApplication.run(Application.class, args);
	}
}
------------------------------------------------------


What is @SpringBootApplication annotation : https://www.youtube.com/watch?v=nUogZ3iSfgc

How run method works in internally : https://www.youtube.com/watch?v=1c0rhNuyC9M

====================================
Working with Banner in SpringBoot ?
====================================

=> When we run boot application then spring logo printing on the console that is called as banner.

=> We can customize banner text based on requirement.

=> Create "banner.txt" file under "src/main/resources" folder with required content.

=> Banner content we can generate from URL

	URL : https://patorjk.com/software/taag/#p=display&f=Graffiti&t=Type%20Something%20
	

=> SpringBoot banner works based on modes.

			a) OFF
			b) LOG
			c) CONSOLE (default)
			
=> We can change banner mode using application.properties file 

spring.main.banner-mode=off			

===================================
What is Runner in the SpringBoot ?
===================================

=> Runners are used to execute the logic only one time when boot application got started.

=> Runners will be called as part of  start class run () method.

=> In Springboot we can create 2 types of runners 

		1) CommandLine Runner (FI)
		
		2) ApplicationRunner (FI)
		

Note: The above interfaces are functional interfaces means only one abstract method available.		

-------------------------------------------
@Component
public class MyCmdRunner implements CommandLineRunner {

	public MyCmdRunner() {
		System.out.println("MyCmdRunner::Constructor");
	}

	@Override
	public void run(String... args) throws Exception {
		System.out.println("cmdRunner - run() called........");
	}
}
---------------------------------------------------


===================================
Real-Time scenarios to use Runners 
===================================

1) load static data from db to cache

2) clean up temporary/staging tables data

---------------------------------------------

------------------------------------------------------


=======================
What is Spring Bean ?
=======================

=> The java class which is managed by IOC is called as spring bean.

=> To represent java class as spring bean we have several annotations like below


@Component ==> independent java classes

@Service ===> Business logic (impl classes)

@Repository ===> DB communication classes

@Configuration => To represent class as config 

@Bean ===> Method level annotation

@Controller ===> To handle C 2 B requests

@RestController ==> To handle B 2 B requests

=================
What is IOC & DI 
=================

=> IOC means inversion of control 

=> IoC is used to manage and colloborate objects in the application.

=> IoC will take care of dependency injection.

===============================
What is Dependency Injection ?
===============================

=> The process of injecting one class object into another class object is called as Dependency Injection.

=> We can perform DI in 3 ways 

	1) Setter Injection 
	2) Constructor Injection 
	3) Field Injection	

=> To perform Dependency Injection we will use @Autowired annotation.

=> Autowired annotation we can write at 3 places 

		a) setter method level (SI)
		b) constructor level (CI)
		c) field level (FI)

=============================================================
How to access private variables outside of the class ?
=============================================================

package in.ashokit.beans;

import java.lang.reflect.Field;

public class Test {

	@SuppressWarnings("deprecation")
	public static void main(String[] args) throws Exception {

		// load java class into jvm
		Class<?> forName = Class.forName("in.ashokit.beans.User");

		// load class variable
		Field field = forName.getDeclaredField("age");

		// give access for variable
		field.setAccessible(true);

		// getting obj of loaded class
		Object newInstance = forName.newInstance();

		// type casting
		User u = (User) newInstance;

		u.getAge();

		// set value to private variable
		field.set(newInstance, 30);

		u.getAge();

	}
}





1) What is SpringBoot
2) What we can build using Springboot
3) Advantages with SpringBoot
		- POM starters
		- Auto Configuration
		- Embedded containers
		- Actuators
		- Rapid Development
4) Creating Boot Application
5) Boot App folder structure
6) Start class in SpringBoot
7) What is @SpringBootApplication annotation
8) What is Component Scanning
9) How run() method works internally
10) Banner in springboot
11) Runners in SpringBoot
12) What is IOC 
13) What is Dependency Injection (CI + SI + FI)
14) How field injection works internally ?
15) Spring Annotations
16) What is Spring Bean 
17) Spring Bean Scopes
18) Spring Bean Life Cycle



1) Spring Core
2) Spring JDBC
3) Spring Boot