=============
Spring Boot 
=============

=> Spring framework available in market from 2004 onwards...

=> Spring Boot came into market in the year of 2015...

=> Spring Boot is an extension for spring framework.

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

=> Using springboot we can develop several types of applications.

		1) stand-alone apps (cli)

		2) web apps (C 2 B)

		3) distributed apps (B 2 B) (webservices)

=> If we develop project using spring then we need to manage configurations on our own.

=> If we develop project using springboot then we will get Auto Configuration.

=> Using springboot we can achieve rapid application development.

===========================
Advantages with springboot
===========================

1) POM starters

2) Auto Configuration

3) Embedded Servers

4) Actuators (monitoring and management)


#### pom starters (maven dependencies) : Simplifying maven dependencies in pom.xml file.

	a) web-starter

	b) data-jpa-starter

	c) mail-starter

	d) security-starter

	e) actuator-starter

Note: pom starters are used to enable auto configurations in boot application.


#### Auto Configuration

=> Based on pom starters boot will identify configurations required for the project and boot will manage those configurations in runtime of our application.

		web-starter ====> tomcat server

		security-starter ===> default login page for authentication

		jpa-starter ===> db connection pool

		actuator-starter ===> monitoring support

#### Embedded Servers

=> Springboot will take care of servers to run our web applications 
  (we no need to download & install server)

=> Springboot will support 3 embedded containers

		1) tomcat (default)

		2) jetty

		3) netty


#### Actuators (production ready features)		

=> Actuators are used to monitor and manage our applications.

		- check health
		- classes loaded
		- check url patterns
		- thread pool
		- heap memory


==========================
How to install STS IDE
==========================

1) download sts ide jar file

STS Download Link : https://cdn.spring.io/spring-tools/release/STS4/4.24.0.RELEASE/dist/e4.32/spring-tool-suite-4-4.24.0.RELEASE-e4.32.0-win32.win32.x86_64.self-extracting.jar

2) run that jar file from cmd

syntax : java -jar <file-name>

3) Go to sts folder and open "SpringToolSuite4.exe" file

=============================
How to install IntelliJ IDE
=============================

1) Download IntelliJ community version (free of cost)

Download Link : https://www.jetbrains.com/idea/download/download-thanks.html?platform=windows&code=IIC

2) Once .exe file is downloaded double click and install it.		


=====================================
How to create springboot project ?
=====================================		

## Approach-1 : Create boot application using "spring intializer website" then download it and extract it and import into "Eclipse / STS / intelliJ" IDE.

		URL : start.spring.io

## Approach-2 : Use STS ide to create springboot application directley.	


======================================
Springboot project folder structure
======================================

sb-app

	- src/main/java ===========> project source code

			- Application.java ----> start/main class of spring boot app (entry point)

	- src/main/resources ===========> config files (xml,yml,props)

			- application.properties ----> config props

	- src/test/java =========> unit test classes (junits)

			- ApplicationTests.java -----> Junit class

	- Maven dependencies =====> jars downloaded

	- target (.class files goes here)

	- pom.xml ======> maven config file


======================================
What is spring-boot-starter-parent ?	
======================================

=> The "spring-boot-starter-parent" is a special starter in Spring Boot projects. 

=> "spring-boot-starter-parent" acts as parent project for our springboot projects.

=> parent-starter will provide below functionalities

		1) default configurations

		2) manages dependency versions

		3) Reduces boiler plate code

============================================
How to change embedded server port number ?
============================================

=> SpringBoot embedded server runs by default on 8080 port.

=> By adding "server.port" property in application.properties file we can change port number

server.port=9090


==================================
What is dev-tools in springboot ?
==================================

=> Devtools is a maven dependency that we can add in springboot app pom.xml file..

=> It is used to auto restart our embedded servers when there is a code change in our application.

<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-devtools</artifactId>
</dependency>


=====================================
What is start class in springboot ?
=====================================

@SpringBootApplication
public class Application {

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

=> This start class will be created by default when boot app got created.

=> Start class is also called as main class of springboot application.

=> It is entrypoint for boot application execution. Execution will start from here only.


========================================
How run () method works internally ?
========================================

- start the timer

- create bootstrap context

- load listner classes

- prepare environment (read props/yml file)

- print banner

- create application-context (ioc)

- prepare and refresh IOC (DI)

- stop the timer

- calculate time taken to start application and print on console

- call runners

- return IOC obj


====================================================================
Q) How IOC container will be started in Springboot application ?
====================================================================

=> run ( ) method will take care of starting IOC container.

=> run ( ) will  use below classes to start IOC container based on starter available in pom.xml

spring-boot-starter :: AnnotationConfigApplicationContext

spring-boot-starter-web :: AnnotationConfigServletWebServerApplicationContext

spring-boot-starter-webflux :: AnnotationConfigReactiveWebServerApplicationContext

Note-1: when we use "web-starter" boot will give "tomcat" as default embedded container. 

Note-2:When we use "webflux-starter" boot will give "netty" as default embedded container.


=================================
What is banner in springboot ?
=================================

=> When we run boot application by default spring logo will be printed on console that is called as banner in springboot.

Note: run ( ) method contains logic to print the banner.

=> We can change banner text according to our requirement by creating "banner.txt" file in "src/main/resources" folder.

=> springboot banner works based on modes. We have 3 types of modes here

		1) console (default)
		2) log
		3) off

========================================
What is return type of run ( ) method ?	
========================================

=> run ( ) method returns ioc container obj using ConfigurableApplicationContext (interface)

ConfigurableApplicationContext context = 
				SpringApplication.run(Application.class, args)	

Note: in the above code, context variable is holding interface impl class obj.

=================================
What is runner in springboot ?
=================================

-> runners are used to execute the logic only one time when boot application started.

ex-1: load data from db table to cache memory when app started

ex-2: clean up temp tables data when app started

ex-3: Send email when our application got started.

Note: run() method will call runners available in springboot app.

================================================
Q) What is @SpringBootApplication annotation ?
================================================

=> This is used at start class of the springboot.

=> This annotation is equal to below 3 annotations

				- @SpringBootConfiguration
				- @EnableAutoConfiguration
				- @ComponentScan

@SpringBootConfiguration : Indicates that this class provides Spring Boot application configuration.

@EnableAutoConfiguration : Tells Spring Boot to automatically configure your application based on the dependencies you have in your classpath.

@ComponentScan : Automatically discovers and registers spring beans in the specified packages.

==============================================================
Q) What is component scanning and how it works internally ?
==============================================================

=> It is the process of identifying spring beans available in the project.

=> Component Scanning will start from base pacakge (the package which contains start class).

=> Once base package scanning completed, then it will go for sub packages of base package.

Note: Any package name which is starting with base package name is called as sub package.

			in.ashokit  --------------------- (base package)

			in.ashokit.beans ------------- will be scanned

			in.ashokit.dao --------------- will be scanned

			in.ashokit.service ----------- will be scanned

			com.tcs.beans ------------------- will not be scanned


Note: We can configure more than one base package using @ComponentScan annotation like below.

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

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

==================================================
Q) How to represent java class as Spring Bean ?
==================================================

=> We have several annotations to represent our java class as Spring bean.

@Component 

@Service

@Repository

@Configuration

@Bean

@Controller

@RestController

##### Note: Springbean classes will be managed by IOC container.


==============================================
Q) @Component Vs @Service Vs @Repository
==============================================

=> These 3 annotations are part of spring framework and we can use in springboot also.

=> These annotations are also called as stereotype annotations.

=> By Using these 3 annotations we can represent java classes as spring beans.

Note: These 3 annotations are class level annotations.

Note: If we represent java class as spring bean then IOC will manage our class (obj creation, dependency injection).

=================
1. @Component
=================

-> General-purpose stereotype.

-> Indicates that the class is a Spring-managed component.

-> Spring will autodetect this class through classpath scanning and register it as a bean.

@Component
public class Engine {

}

=================
2. @Service
=================

-> Specialization of @Component.

-> It is used to annotate service layer classes.

-> Semantically tells the developer and Spring that this class contains business logic.

@Service
public class BookService {
	
}

=================
3. @Repostiory
=================

-> Another specialization of @Component.

=> It is Used to annotate DAO (Data Access Object) classes.

=> It provides additional benefits like automatic exception translation from persistence-specific exceptions (like JDBC exceptions) into Spring’s DataAccessException.

@Repository
public class UserDao {
	
}

============================
Q) What is @Bean annotation
============================

=> It is method level annotation.

=> It is used when we want to customize bean obj creation.

@Bean
public AppSecurity createInstance() {
	// logic
	return new AppSecurity("SHA-256");
}

=======================================
Q) What is @Configuration annotation ?
=======================================

=> It is used to represent java class as configuration class.

=> This configuration class is used as replacement for xml configuration.

---------------------------------------------------------------------
<bean id="myService" class="com.example.MyService"/>

<bean id="myRepository" class="com.example.MyRepository"/>
--------------------------------------------------------------------
@Configuration
public class AppConfig {

    @Bean
    public MyService myService() {
        return new MyService();
    }

    @Bean
    public MyRepository myRepository() {
        return new MyRepository();
    }
}
-----------------------------------------------------------------------

=========================
Runners in Springboot
=========================

-> Runners are used to execute any logic only once when the boot application got started.

-> Runners will be called by SpringApplication.run () method.

## use cases: 

1) To delete temporary tables data when app started

2) load static tables data into cache memory when app started.

=> We have 2 types of runners in springboot

		1) Application Runner (FI)  ==> run (..)

		2) CommandLine Runner (FI) ==> run (..)

------------------------------------------------------------------
@Component
public class MyAppRunner implements ApplicationRunner {

	@Override
	public void run(ApplicationArguments args) throws Exception {
		System.out.println("AppRunner executed...");
	}
}
------------------------------------------------------------------
@Component
public class MyCmdRunner implements CommandLineRunner {

	@Override
	public void run(String... args) throws Exception {
		System.out.println("MyCmdRunner executed...");
	}
}

=======================
Project Architecture
=======================

=> In one project we will create Multiple classes like below

	ex : Controller classes

		 Service classes

		 Dao classes

		 Model or DTO classes

		 Entity classes

=> Controllers are used to handle user request and response.

=> Service classes are used to handle business logic.

=> Dao classes are used to perform DB operations.

=> model and dto classes are used to represent data in the form of object.

=> Entity classes are used to represent table structure for ORM operations.


=> By using all these classes we will create Layered Architecture for our project.


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

=> One class method should call another class method for request processing/execution.
	
	controller method () ---> service method () --------> dao method ( ) 

=> To call one class method from another class method we need to perform Dependency Injection.

=> The process of injecting one class obj into another class obj is called as dependency injection (DI).

Ex: 
		controller class method should call service class method
		(inject service obj into controller)

		Service class method should call dao class method
		(inject dao obj into service)


=> Dependency Injection we can perform in 3 ways

			1) Setter Injection

			2) Constructor Injection

			3) Field Injection

=> IOC container is responsible to perform dependency injection in our applications.

=> By using Autowiring we will tell IOC to perform Dependency Injection.

=> To perform DI with Autowiring we will use @Autowired annoation

=> @Autowired annotation we can use at 3 places

			 - setter method level (SI)

	 		 - constructor level (CI)

			 - field/variable level (FI)


=> Injecting dependent obj into target obj using target class setter method is called as setter injection (S.I).

@Component
public class UserService {

	private UserDao userDao;

	@Autowired
	public void setUserDao(UserDao userDao) {
		this.userDao = userDao;
	}

	public void printName(int id) {
		String nameById = userDao.findNameById(id);
		System.out.println(nameById);
	}
}



===============================================================

1) Spring vs Spring Boot

2) what is springboot ?

3) What are the advantages with SpringBoot ?

4) How to create a springboot project ?

5) What is folder structure of springboot app ?

6) What is start class in springboot ?

7) How run () method works internally in springboot ?

8) How IOC container will be started in Springboot application ?

9) What is banner in springboot and how to customize it ?

10) What is Runner in springboot ?

11) What is the return type of run () method in springboot start class ?

12) What is @SpringBootApplication annotation ?

13) What is Auto Configuration in SpringBoot & how it works ?

14) What is Component Scanning and how it works in background ?

15) Can we configure more than one base package and how to do it?

16) How to represent java class as a Spring Bean ?

17) @Component Vs @Service Vs @Repository annotations

18) What is @Configuration and @Bean annotation.