Spring Short Notes.txt

1. What is Spring?
Spring is a lightweight and flexible framework for Java-based applications that provides comprehensive infrastructure support. It simplifies Java development by offering features like Dependency Injection (DI), Aspect-Oriented Programming (AOP), and data access abstraction.
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2. Architecture of Spring
•	Core Container: Provides basic Spring functionality like Dependency Injection (DI) and IoC.
•	AOP (Aspect-Oriented Programming): Allows separation of cross-cutting concerns, like logging or transaction management.
•	Data Access Layer: Supports data access technologies like JDBC, JPA, Hibernate, etc.
•	Spring MVC/Web: Facilitates web applications using the Model-View-Controller (MVC) pattern.
•	Spring Boot: Allows rapid development of Spring applications with embedded servers and auto-configuration.
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3. Some Modules of Spring
•	Spring Core: The foundation of the Spring framework, providing DI and IoC.
•	Spring AOP: Enables aspect-oriented programming to manage cross-cutting concerns like logging and security.
•	Spring Data: Simplifies access to databases, supporting JPA, JDBC, and NoSQL databases.
•	Spring MVC: Helps in building web applications using the MVC architecture.
•	Spring Security: Provides features for authentication and authorization.
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4. What is Dependency Injection (DI)?
Dependency Injection is a design pattern where an object's dependencies are provided externally rather than the object creating them. This promotes loose coupling and enhances testability.
Example:
public class Car {
    private Engine engine;

    @Autowired
    public Car(Engine engine) {
        this.engine = engine;
    }
}
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5. What is Inversion of Control (IoC)?
IoC is a design principle where the control of object creation and management is transferred from the object itself to an external framework (like Spring). Spring achieves IoC using Dependency Injection.
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6. Different Ways to Configure Spring Dependency Injection
1.	XML Configuration:
<bean id="myBean" class="com.example.MyBean"/>
2.	Java-based Configuration:
java
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@Configuration
public class AppConfig {
    @Bean
    public MyBean myBean() {
        return new MyBean();
    }
}


3.	Annotation-based Configuration:
@Component
public class MyBean {}

@Autowired
private MyBean myBean;
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7. What is Loosely Coupled?
In loosely coupled systems, components are independent and don’t rely on direct knowledge of each other. This modularity improves maintainability and testability.
Example: In DI, a class does not create its own dependencies but relies on Spring to inject them, thus reducing coupling.
public class Car {
    @Autowired
    private Engine engine; // Spring injects the dependency
}
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8. Spring Annotations
1.	@Bean: Defines a bean in Java-based configuration.
@Bean
public Car car() {
    return new Car();
}
2.	@Component: Marks a class as a Spring bean.
java
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@Component
public class Engine {}
3.	@Configuration: Indicates a class that contains @Bean methods.
@Configuration
public class AppConfig {}
4.	@ComponentScan: Configures Spring to scan for components in specified packages.
@ComponentScan(basePackages = "com.example")
public class AppConfig {}
5.	@Autowired: Marks a field or constructor for automatic dependency injection.
@Autowired
private Engine engine;
6.	@Qualifier: Resolves ambiguity when multiple beans of the same type are present.
@Autowired
@Qualifier("v6Engine")
private Engine engine;
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9. How to Read Value from Properties File?
You can read properties from a file using the @Value annotation or Environment interface.
Example:
@Value("${database.url}")
private String databaseUrl;
Configuration:
@Configuration
@PropertySource("classpath:application.properties")
public class AppConfig {}
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10. Bean Scope in Spring
1.	Singleton: A single instance of the bean is created for the entire Spring container (default).
@Component
public class SingletonBean {}
2.	Prototype: A new instance is created every time the bean is requested.
@Component
@Scope("prototype")
public class PrototypeBean {}
3.	Request: A new bean is created for each HTTP request (Web context).
@Scope("request")
public class RequestBean {}
4.	Session: A new bean is created for each HTTP session (Web context).
@Scope("session")
public class SessionBean {}
5.	Global-Session: Used for Portlet-based web applications (similar to session scope).
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