What is Autoconfiguration in Spring boot and how to override

What is AutoConfiguration in Spring Boot?

In Spring Boot, auto-configuration is a powerful mechanism that automatically configures beans and other components based on the classpath and available beans, eliminating the need for manual configuration in most cases. It is part of the Spring Boot Starter infrastructure and aims to make it as easy as possible to set up a Spring-based application.

Spring Boot auto-configures your application based on the dependencies you have in the classpath, allowing developers to focus on writing application-specific logic instead of worrying about complex configurations. It does this using @EnableAutoConfiguration or @SpringBootApplication (which includes @EnableAutoConfiguration), and it uses a set of predefined configurations and conditions to automatically configure various Spring beans, data sources, messaging, security, etc.

How Does AutoConfiguration Work?

Conditional Configuration: Spring Boot uses @Conditional annotations, which ensure that auto-configuration happens only if certain conditions are met, such as the presence of a class on the classpath or a specific configuration setting.
Spring Boot Starters: Spring Boot provides "starters" that are a set of dependency descriptors to include common libraries needed for specific use cases (e.g., spring-boot-starter-data-jpa, spring-boot-starter-web, etc.). Each starter comes with its own auto-configuration logic.
Configuration Classes: Auto-configuration is implemented using Java classes annotated with @Configuration that define beans. These classes are conditionally applied depending on the environment and the libraries present in the classpath.
Example of AutoConfiguration: If you add spring-boot-starter-data-jpa to your classpath, Spring Boot will automatically configure a DataSource bean, an EntityManagerFactory bean, and other JPA-related beans without you needing to write any configuration.

Auto-Configuration in Action

When you run a Spring Boot application, Spring Boot automatically applies configurations based on your project’s dependencies. Here’s a basic example:

Add a Dependency: For example, if you add the spring-boot-starter-web dependency, Spring Boot will automatically configure Tomcat as the default embedded web server, configure a dispatcher servlet, etc.

&lt;dependency&gt;
   &lt;groupId&gt;org.springframework.boot&lt;/groupId&gt;
   &lt;artifactId&gt;spring-boot-starter-web&lt;/artifactId&gt;
&lt;/dependency&gt;

<groupId>org.springframework.boot</groupId>

<artifactId>spring-boot-starter-web</artifactId>

</dependency>

Enable Auto-Configuration: In your Spring Boot application, you don’t need to specify a lot of configuration for web-related beans. By adding the dependency, Spring Boot will automatically enable things like:
- Servlet container (Tomcat, Jetty, etc.)
- Default error handling
- DispatcherServlet
- Spring MVC Configuration

How to Override Auto-Configuration?

Although Spring Boot auto-configuration is convenient, there are times when you need to override or customize the behavior of auto-configured beans. Here’s how you can do it:

1. Disable Specific Auto-Configuration

Sometimes, you might want to disable a specific auto-configuration. You can do this using the @EnableAutoConfiguration annotation with the exclude attribute or by using @SpringBootApplication (which includes @EnableAutoConfiguration).

Example: Disabling a Specific Auto-Configuration

@SpringBootApplication(exclude = {DataSourceAutoConfiguration.class})
public class MyApplication {
    public static void main(String[] args) {
        SpringApplication.run(MyApplication.class, args);
    }
}

@SpringBootApplication(exclude = {DataSourceAutoConfiguration.class})

public class MyApplication {

public static void main(String[] args) {

SpringApplication.run(MyApplication.class, args);

}

This excludes the automatic configuration of the DataSource bean, which may be useful if you want to manually configure your own database connection.

2. Create Your Own Custom AutoConfiguration

If you want to write your own auto-configuration or override existing auto-configuration, you can create a custom @Configuration class that is conditionally applied based on certain conditions.

Example: Custom Auto-Configuration

You can write your own auto-configuration class like this:

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;

@Configuration
public class MyCustomAutoConfiguration {

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

import org.springframework.context.annotation.Bean;

import org.springframework.context.annotation.Configuration;

import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;

@Configuration

public class MyCustomAutoConfiguration {

@Bean

@ConditionalOnMissingBean

public MyService myService() {

return new MyServiceImpl();

}

Here, @ConditionalOnMissingBean ensures that the bean is created only if no other MyService bean is already present in the application context. You can use other conditions like @ConditionalOnClass, @ConditionalOnProperty, etc.

3. Override Auto-Configured Beans

If you want to override an auto-configured bean (for example, replacing the default DataSource bean with your custom implementation), you can define your own bean in a configuration class.

Example: Overriding Auto-Configured DataSource Bean

By default, Spring Boot will auto-configure a DataSource bean if the necessary properties are provided. If you want to provide your own custom DataSource, you can simply define it in a configuration class:

import org.springframework.boot.jdbc.DataSourceBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import javax.sql.DataSource;

@Configuration
public class MyDatabaseConfig {

    @Bean
    public DataSource dataSource() {
        return DataSourceBuilder.create()
                .url("jdbc:mysql://localhost:3306/mydb")
                .username("user")
                .password("password")
                .driverClassName("com.mysql.cj.jdbc.Driver")
                .build();
    }
}

import org.springframework.boot.jdbc.DataSourceBuilder;

import org.springframework.context.annotation.Bean;

import org.springframework.context.annotation.Configuration;

import javax.sql.DataSource;

@Configuration

public class MyDatabaseConfig {

@Bean

public DataSource dataSource() {

return DataSourceBuilder.create()

.url("jdbc:mysql://localhost:3306/mydb")

.username("user")

.password("password")

.driverClassName("com.mysql.cj.jdbc.Driver")

.build();

}

This custom DataSource bean will override the default one configured by Spring Boot’s auto-configuration.

4. Use `@ConditionalOnProperty` to Control Auto-Configuration

Spring Boot auto-configuration can also be controlled based on properties in application.properties or application.yml. For instance, you can specify that a certain auto-configuration class should only be applied if a specific property is set.

Example: Conditional Auto-Configuration Based on a Property

@Configuration
@ConditionalOnProperty(name = "myapp.feature.enabled", havingValue = "true")
public class MyFeatureAutoConfiguration {
    // Bean definitions for this feature
}

@Configuration

@ConditionalOnProperty(name = "myapp.feature.enabled", havingValue = "true")

public class MyFeatureAutoConfiguration {

// Bean definitions for this feature

}

In the application.properties:

myapp.feature.enabled=true

1	myapp.feature.enabled=true

This configuration ensures that MyFeatureAutoConfiguration is only applied if the myapp.feature.enabled property is set to true.

5. Use Profiles to Control Auto-Configuration

You can use Spring profiles to define different auto-configuration logic for different environments (e.g., development, production).

Example: Profile-Based Auto-Configuration

@Configuration
@Profile("dev")
public class DevDatabaseConfig {
    // Define beans for dev environment
}

@Configuration
@Profile("prod")
public class ProdDatabaseConfig {
    // Define beans for production environment
}

@Configuration

@Profile("dev")

public class DevDatabaseConfig {

// Define beans for dev environment

}

@Configuration

@Profile("prod")

public class ProdDatabaseConfig {

// Define beans for production environment

}

Then, in application.properties, you can specify the active profile:

spring.profiles.active=dev

1	spring.profiles.active=dev

Summary

Auto-configuration in Spring Boot helps you configure beans based on the classpath and the environment without manual setup.
To override auto-configuration, you can:
- Use exclude to disable a specific auto-configuration class.
- Create your own custom auto-configuration class.
- Override auto-configured beans by defining your own beans in configuration classes.
- Use @ConditionalOnProperty to enable/disable auto-configuration based on properties.
- Control auto-configuration with Spring profiles (@Profile).

New Dev Point

Some problems explained

What is Autoconfiguration in Spring boot and how to override

What is AutoConfiguration in Spring Boot?

How Does AutoConfiguration Work?

Auto-Configuration in Action

How to Override Auto-Configuration?

1. Disable Specific Auto-Configuration

2. Create Your Own Custom AutoConfiguration

3. Override Auto-Configured Beans

4. Use `@ConditionalOnProperty` to Control Auto-Configuration

5. Use Profiles to Control Auto-Configuration

Summary

What is AutoConfiguration in Spring Boot?

How Does AutoConfiguration Work?

Auto-Configuration in Action

How to Override Auto-Configuration?

1. Disable Specific Auto-Configuration

2. Create Your Own Custom AutoConfiguration

3. Override Auto-Configured Beans

4. Use @ConditionalOnProperty to Control Auto-Configuration

5. Use Profiles to Control Auto-Configuration

Summary

4. Use `@ConditionalOnProperty` to Control Auto-Configuration