Spring Boot Configuration/Autoconfiguration

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This chapter will discuss in detail about Spring Boot configuration and auto-configuration.

Spring Boot Configuration

Although a Spring/Spring Boot application can be configured in an XML document, it is generally recommended to configure Spring Boot applications with a single file with @Configuration annotation.

Different kinds of annotation

@Component Annotation

In Spring Boot, the @Component annotation declares a class as a Spring component. This signals to Spring that the class should be managed by the Spring container, meaning it will be automatically created, initialized, and potentially injected into other components.

Example

import org.springframework.stereotype.Component;

@Component
public class Utility {
...
}

@Configuration Annotation

In Spring Boot, the @Configuration annotation is used to indicate that a class is a source of bean definitions. It's a core annotation from the Spring Framework, not specific to Spring Boot. Classes marked with @Configuration can define beans using the @Bean annotation on methods within the class. These beans are then managed by the Spring container. @Configuration promotes a Java-based configuration approach instead of relying solely on XML configuration files.

Example

@Configuration
public class AppConfig {

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

@SpringBootApplication Annotation

This is a meta-annotation that combines @EnableAutoConfiguration, @ComponentScan, and @Configuration. It's often the only annotation you need to bootstrap a Spring Boot application.

Example

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.ComponentScan;

@SpringBootApplication
public class MyApplication {

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

@ComponentScan Annotation

In Spring Boot, the @ComponentScan annotation is used to instruct Spring to scan the specified packages and their sub-packages for components (classes annotated with @Component, @Service, @Repository, @Controller, etc.) and register them as beans in the Spring application context. By default, if you don't explicitly use @ComponentScan, Spring Boot automatically scans the package where your main application class resides and its sub-packages. If your components are in a different package structure, you can use basePackages attribute of @ComponentScan to specify the packages to scan. You can specify multiple packages using an array in basePackages, e.g.,

basePackages = {"com.example.package1", "com.example.package2"}

Example

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.ComponentScan;

@SpringBootApplication
@ComponentScan(basePackages = {"com.example.mypackage"}) 
public class MyApplication {

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

What is Spring Boot Autoconfiguration?

Spring Boot Autoconfiguration is a feature that automatically configures your Spring application based on the dependencies present on the classpath and various properties settings. This eliminates the need for a lot of manual configuration, making Spring Boot applications easier to set up and maintain.

@SpringBootApplication or @EnableAutoConfiguration Annotation

These annotations trigger the autoconfiguration process. Typically, you annotate your main application class with @SpringBootApplication, which includes @EnableAutoConfiguration. Additional packages can be configured using the @AutoConfigurationPackage annotation.

• Scanning the Classpath − Spring Boot scans the classpath for libraries and frameworks.

• Conditional Configuration − Based on the detected dependencies, Spring Boot applies relevant configurations. This is done using @Conditional annotations, such as:

  • @ConditionalOnClass− Applies configuration if a specific class is present on the classpath.

  • @ConditionalOnMissingBean− Applies configuration if a specific bean is not already defined.

  • @ConditionalOnProperty− Applies configuration based on property values.

• Bean Creation and Configuration − Spring Boot creates and configures beans based on the applied autoconfigurations.

  Example:

  • If you add the spring-boot-starter-web dependency to your project, Spring Boot automatically configures a Tomcat web server and other necessary components for a web application.

  • If you add the spring-boot-starter-data-jpa dependency, Spring Boot automatically configures a data source, entity manager, and other components required for JPA-based data access.

Benefits of Spring Boot Autoconfiguration

Following are some of the major benefits of using Spring Boot Autoconfiguration.

• Reduced Boilerplate Code− Autoconfiguration eliminates the need for manual configuration of common Spring components.

• Faster Development− You can quickly create Spring Boot applications without having to write extensive configuration code.

• Improved Productivity− Autoconfiguration allows you to focus on the core business logic of your application.

• Customization− You can customize the autoconfiguration behavior by following means:

  • Excluding specific autoconfiguration classes using the exclude attribute of @EnableAutoConfiguration.

  • Defining your own beans to override the auto-configured ones.

  • Using property files or environment variables to modify the default configurations.