#################################
Date : 26-Jul-2024
Topic : Spring Boot Introduction
#################################

=> Spring Boot is an extension for spring framework.

=> Spring Boot is an approach to develop spring based application with less configuration.

=> Using springboot we can develop several types of applications

			a) standalone applications
			b) web applications ( C 2 B )
			c) distributed applications (B 2 B)

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

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

Note: Spring boot will identify configurations required for the project and it will provide those configurations.

		- starting ioc container
		- component scanning
		- create connection pool
		- start embedded server
		- default security

=> Using springboot we can achieve rapid application development.

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

1) pom starters (dependencies)

		a) web-starter
		b) jpa-starter
		c) security-starter
		d) mail-starter
		e) actuator-starter etc...

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

2) Auto Configuration

=> Based on pom starters boot will identify configurations required for the project and boot will manage those configuration.


		web-starter ===> tomcat server

		jpa-starter ===> connection pooling

		security-starter => default login page

		actuator-starter => monitoring

3) Embedded Servers/Containers

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

=> Springboot will support 3 embedded containers

		a) tomcat (default)
		b) jetty
		c) netty

4) Actuators (production read features)

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

		- check health
		- check beans loaded
		- check url patterns
		- check threads
		- chek heap memory

5) Component Scanning

=> Using component scanning springboot will scan our project packages and it will identify spring beans.


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

Approach-1 : Create boot application using spring intializer website then download it and extract it and import into eclipse / intelliJ IDE

			URL : start.spring.io

Note: IntelliJ ultimate version will support springboot project creatin directley. IntelliJ ultimate is licensed.

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

Note: STS ide will communicate with intializr website to download project.

Note: To create springboot application internet is mandatory.


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

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.

#################################
Date : 27-Jul-2024
Topic : Spring Boot project
#################################

1) Creating Springboot application

2) Playing with pom starters

3) Understanding springboot project folder structure

4) Running springboot application

5) Internals of Springboot (postportam for start class)

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

spring-boot-app

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

	    - Application.java ====> main/start class

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

	    - static  (images goes here)

	    - templates (html files goes here)

	 		- application.properties ===> configurations

	 - 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


#################################
Date : 29-Jul-2024
Topic : Spring Boot Internals
#################################	 

1) What is start class in springboot

2) What is run () method in springboot

3) Internals of run () method

4) what is @SpringBootApplication annotation

5) What is component scanning ?

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

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

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

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


====================================================================
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 wil 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.

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

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

=> We can set banner mode using "application.properties" file		

		spring.main.banner-mode=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.


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

- start the timer
- create bootstrap context
- load listner classes
- start the listners
- prepare environment (read props/yml file)
- create application-context (ioc)
- prepare and refresh IOC (DI)
- stop the timer
- calculate time taken and print on console
- call runners
- return IOC obj


=============
Assignment
=============
What is @SpringBootApplication annotation ? 

What is Component Scanning ?

#################################
Date : 30-Jul-2024
Topic : Spring Boot Internals
#################################	 


Q) How to represent java class as Spring Bean ?

=> We can use below annotations to represent java class as springbean. 

@Component
@Service
@Repository

@Configuration-----------> java class as configuration class
@Bean -------------------> method level annotation

@Controller
@RestController


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

=================================
Q) What is component scanning ?
=================================

=> 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 is called as sub package.

Ex:

		in.ashokit--------------------------- will be scanned
			  - Application.java

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

    in.ashokit.security ------------------ will be scanned

    com.oracle.util  --------------------- will not be scanned


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

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

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


=============================
What is @Bean annotation ?
=============================

=> It is method level annotation. It is used to customize bean obj creation.

@Configuration
public class AppConfig {

	@Bean
	public AppSecurity createAppSecurity() {
		System.out.println("security app method called....");
		AppSecurity security = new AppSecurity("AES");
		return security;
	}
}

Note: It is recommended to keep @Bean methods in configuration class. SpringBoot start class also acts as configuration class.


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

================
Assignment :
================

1) Bean Scopes
2) Bean Life Cycle


#################################
Date : 31-Jul-2024
Topic : Bean Scopes
#################################

==============
Bean Scopes
==============

=> Bean scope will represent how many objects should be created for a spring bean.

=> We have below 4 scopes

					1) singleton (default)
					2) prototype
					3) request
					4) session

=> If we don't specify any scope then by default it will consider as signleton scope.

Note: For singleton scoped beans only one object will be created. Singleton beans are eager loading beans that means when ioc container started then immediatley objects will be created for singleton beans.

Note: When we call getBean ( ) method IOC will return existing obj of singleton bean.					


=> Prototype beans are lazy loading beans that means when we call getBean() method then only new object will be created. Multiple objs will be created for prototype beans.

@Component
@Scope("prototype")
public class UserService {

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

}

Note: request and session scopes are related to spring web mvc module.


==========
Summary
=========

1) What is Springboot

2) Advantages with SpringBoot
			 - pom starters
			 - auto configuration
			 - embedded servers
			 - actuators
			 - component scanning

3) SpringBoot application development	

4) SpringBoot application project folder structure

5) Start class in springboot

6) Internals of SpringApplication.run ( ) method

7) What is @SpringBootApplication annotation 

8) What is component scanning

				 - base package
				 - sub package

9) How to represent java class as Spring Bean

				 - @Component
				 - @Configuration
				 - @Bean

10) Bean Scopes

				 - singleton
				 - prototype
				 - request
				 - session

==========================
Assignment : Autowiring
==========================

######################
Date : 02-Aug-2024
Topic : Autowiring
######################

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

	Ex:

		controller should call service method
		(inject service obj into controller)

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


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

=> DI we can perform in 3 ways

			1) Setter Injection (SI)
			2) Constructor Injection (CI)
			3) Field Injection (FI)

=> Autowiring is used 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)

@Autowired
private UserDao dao;

@Autowired
public void setDao(UserDao dao){
		this.dao = dao;
}

@Autowired
public UserService(UserDao dao){
	this.dao = dao;
}


Autowiring works based on modes

1) byName --> based on variabe name it will identify dependent bean object

		private UserDao dao;

2) byType

3) constructor

4) none


@Qualifier(name)

@Primary

=========================
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) 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) ApplicationRunner (FI)		
				- run (..)
		
		2) CommandLineRunner (FI)		
				- run (..)

--------------------------------------------------------
@Component
public class MyAppRunner implements ApplicationRunner{
	
	@Override
	public void run(ApplicationArguments args) throws Exception {
		System.out.println("MyAppRunner :: run () method called..");		
	}
}
---------------------------------------------------------

@Component
public class MyCmdRunner implements CommandLineRunner{
	
	@Override
	public void run(String... args) throws Exception {
		System.out.println("MyCmdRunner :: run() method called..");
	}

}

=================
Bean life cycle
=================

Q) What is spring bean ?

-> The java class which is managed by ioc container is called as spring bean.

-> IOC container will take care of bean life cycle 

			- creating object
			- managing object 
			- destroying object

Note: We have several annotations to represent java class as spring bean.

			@Component
			@Service
			@Repository
			@Bean
			@Controller
			@RestController
			

=> When iOC container managing bean life cycle we can execute life cycle methods using below annotations

			a) @PostConstruct (after obj creation)
			b) @PreDestroy (before obj deletion)
			
----------------------------------------------------------

@Component
public class ReportService {

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

	@PostConstruct
	public void init() {
		System.out.println("ReportService - init () called..");
	}

	@PreDestroy
	public void destroy() {
		System.out.println("ReportService - destroy () called..");
	}

}

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

==========
Summary
=========

1) What is Springboot

2) Advantages with SpringBoot
			 - pom starters
			 - auto configuration
			 - embedded servers
			 - actuators
			 - component scanning

3) SpringBoot application development	

4) SpringBoot application project folder structure

5) Start class in springboot

6) Internals of SpringApplication.run ( ) method

7) What is @SpringBootApplication annotation 

8) What is component scanning
		 - base package
		 - sub package

9) How to represent java class as Spring Bean
		 - @Component
		 - @Configuration
		 - @Bean

10) Bean Scopes
		 - singleton
		 - prototype
		 - request
		 - session
				 
11) Autowiring 
		- byName
		- byType
		- constructor
		
12) Bean Life cycle

		- @PostConstruct
		- @PreDestroy
		
13) Runners in Springboot		

14) Banner in SpringBoot 

15) IOC & DI
	  - setter injection
	  - constructor injection 
	  - field injection
	  
16) Springboot annotation 
	  @Component
	  @Service
	  @Repository
	  @Configuration
	  @Bean
	  @Scope
	  @Autowired
	  @Qualifier
	  @Primary
	  @PostConstruct
	  @PreDestroy
--------------------------------------------
Assignment
-------------------------------------------
1) Database Setup 
	 - MySQL DB Server 
	 - MySQL workbench (Client s/w)
	 
Ref : https://www.youtube.com/watch?v=EsAIXPIsyQg	 

2) Developing First Data JPA app to insert emp record into mysql database table.	

Ref : https://www.youtube.com/watch?v=ZGKHCJsp4hg