Spring @Configuration Annotation

Introduction

The @Configuration annotation is used to declare that the class serves as a Spring configuration class in which we can provide different configurations like bean configurations, database configurations, MVC configurations etc.
Using the @Configuration annotation, we create a Java-based configuration class, which serves as an alternative to XML-based configuration in Spring.
@Configuration annotation is used at class level in Spring. It cannot be used with methods or fields.

Syntax :

import org.springframework.context.annotation.Configuration;

@Configuration
public class AppConfig
{
    /*
        Here we provide the different configurations for example....
        Bean Configurations, Database Configurations, MVC Configurations, Security Configurations etc
    */
}

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Different Configurations within "@Configuration Class"

We can provide different types of configurations in Spring Configuration File which as as follows :-
1. Bean Configurations
2. Database Configurations
3. MVC Configurations
4. Security Configurations
  etc...
Basic definition and its syntax are as below :-

1. Bean Configuration:

One of the most common configurations that we provide in Java Configuration Class is Bean Configurations.
Within Spring Configuration Class annotated with @Configuration annotation, we can provide methods annotated with @Bean to define and configure beans.
Each @Bean method defines the instantiation, initialization, and dependency injection logic for a specific bean.

Syntax :

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class BeanConfig
{
    // Below @Bean annotation is used to create Student class Bean
    @Bean
    public Student stdId() // Here method name is the bean-id / bean-name
    {
        // It will return the Student object
        return new Student();
    }
}

NOTE : When we use @Bean annotated methods, @Configuration ensures that a single instance of each bean is created (singleton), even if methods are called multiple times within the class. This is managed internally by Spring through CGLIB proxying.

2. Database Configuration:

Database configurations are also one of the most common configurations when we use databases with spring application.
In this, we set up data sources, transaction management, and JPA/Hibernate configurations.

Syntax :

//package and import statements

@Configuration
public class DatabaseConfig
{
    @Bean
    public DataSource dataSource()
    {
        DriverManagerDataSource dataSource = new DriverManagerDataSource();
        dataSource.setDriverClassName("com.mysql.cj.jdbc.Driver");
        dataSource.setUrl("jdbc:mysql://localhost:3306/mydb");
        dataSource.setUsername("database-username");
        dataSource.setPassword("database-password");
        return dataSource;
    }
}

NOTE : These types of configuration programs will be covered in Spring with JDBC (Database) Module.

3. MVC Configuration:

MVC Configurations sets-up the MVC-related configurations like view resolvers, message converters, CORS settings, etc

Syntax :

//package and import statements
                                    
@Configuration
public class WebConfig implements WebMvcConfigurer
{
    @Override
    public void addViewControllers(ViewControllerRegistry registry)
    {
        registry.addViewController("/home").setViewName("home");
    }

    @Override
    public void addCorsMappings(CorsRegistry registry)
    {
        registry.addMapping("/**").allowedOrigins("https://example.com");
    }
}

NOTE : These types of configuration programs will be covered in Spring MVC Module.

4. Security Configuration:

Security Configurations configure the applications security, often using Spring Security.

Syntax :

//package and import statements
                                    
@Configuration
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter
{
    @Override
    protected void configure(HttpSecurity http) throws Exception
    {
        http
            .authorizeRequests()
                .antMatchers("/public/**").permitAll()
                .anyRequest().authenticated()
            .and()
            .formLogin();
    }
}

NOTE : These types of configuration programs will be covered in Spring Security Module.

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Spring @Configuration Annotation

Introduction

Different Configurations within "@Configuration Class"

1. Bean Configuration:

2. Database Configuration:

3. MVC Configuration:

4. Security Configuration:

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