1) Advantages of Spring

• Spring is a tool used for developing Java applications quickly

1. Spring is everywhere
   • Spring is everywhere and is trusted globally
   • Popular companies like Amazon, Google, and Microsoft use Spring
   • It supports everything from simple applications to complex applications
2. Spring is Flexible
   • Spring provides flexible libraries that support any type of application
   • It includes
     • Inversion of Control (IoC)
     • Dependency Injection (DI)
3. Spring is Productive
   • Spring adds powerful tools that increase productivity
   • Spring helps to build microservices quickly
4. Spring is Fast
   • Spring allows applications to start, run and shut down quickly
5. Spring is secure
   • Spring keeps the data safe from security vulnerabilities
   • Modern applications are safer with Spring Security
6. Spring is supportive
   • Spring supports developers by providing
     • training
     • certificates, etc...

2) Spring Framework

• Spring Framework is a lightweight and open-source Framework
• It is used for developing Java Applications quickly

Architecture

3) Configuration in IoC Container

• IoC stands for Inversion of Control
• In Java-Based Configuration, Spring uses @configuration and @Beans annotations to define and manage beans in the IoC Container

1. @configuration
   • It is used on classes that contain bean definitions
2. @Bean
   • It is used on methods that define the bean

Syntax

@Configuration
public class A {
  @Bean
  public B fun() {
     ...
  }
}
        

Inter Bean Dependencies

@Configuration
public class A {
  @Bean
  public B fun1() {
     ...
  }
  @Bean
  public C fun2() {
     ...
  }
}
            

Program

@Component
public class A {
  public void display() {
    System.out.println("Hello World");
  }
}
            

@Configuration
public class B{
  @Bean
  public A fun1(){
    return new A();
  }
}
            

public class Main {
  public static void main(String[] args){
    ApplicationContext context = new AnnotationConfigApplicationContext(B.class);
    A obj = context.getBean(A.class);
    obj.display();
  }
}
            

Hello World
            

4) Dependency Injection

• DI stands for Dependency Injection
• In Dependency Injection, it injects one object into another object
• Types of Dependency Injection

1. Constructor Injection
   • Constructor Injection is a type of Dependency Injection
   • Constructor Injection is a technique where dependencies are injected into the class by using a constructor
   • It calls the constructor with required dependencies

   Syntax

   @Component
   public class B {
     @Autowired
     public B(public A a) {
       this.a = a;
     }
   }
                   

   Program

   A.java

   @Component
   public class A {
     public void display() {
       System.out.println("Hello World");
     }
   }
                       

   B.java

   @Component
   public class B{
     @Autowired
     public B(public A a){
       this.a = a;
     }
   }
                       

   Main.java

   public class Main {
     public static void main(String[] args){
       ApplicationContext context = new AnnotationConfigApplicationContext(B.class);
       A obj = context.getBean(A.class);
       obj.display();
     }
   }
                       

   Output

   Hello World
                       

2. Setter Injection
   • Setter Injection is a type of Dependency Injection
   • Setter Injection is a technique where dependencies are injected into the beans by using setter methods
   • It creates the bean and defines the setter methods

   Syntax

   @Component
   public class B {
     @Autowired
     public void fun(public A a) {
       this.a = a;
     }
   }
                   

   Program

   A.java

   @Component
   public class A {
     public void display() {
       System.out.println("Hello World");
     }
   }
                       

   B.java

   @Component
   public class B{
     @Autowired
     public void fun(public A a){
       this.a = a;
     }
   }
                       

   Main.java

   public class Main {
     public static void main(String[] args){
       ApplicationContext context = new AnnotationConfigApplicationContext(B.class);
       A obj = context.getBean(A.class);
       obj.display();
     }
   }
                       

   Output

   Hello World
                       

5) Auto Scanning

• The process of automatically finding and managing Spring components is called as Auto Scanning
• Spring components are
  • beans
  • controllers
  • repositories
  • services
• Annotations are
  • @Component
  • @Controller
  • @Repository
  • @Service

Syntax

@Component
public class A {
   ...
}
@Controller
public class B {
   @Autowired
   ...
}
@Repository
public class C {
   ...
}
@Service
public class D {
   ...
}