How springboot implements automatic assembly

Ways to implement springboot automatic assembly: 1. Java-based configuration; 2. Automatic configuration; 3. Conditional annotations; 4. Automatic assembly; 5. Spring Boot Starter; 6. Automatic assembly of third-party libraries; 7. Customized automatic assembly; 8. Component scanning; 9. Externalized configuration and attribute-driven configuration; 10. Event-driven automatic assembly; 11. Spring Boot starter POMs; 12. Conditional annotations and conditional classes, etc.

The operating system for this tutorial: Windows 10 system, DELL G3 computer.

Spring Boot simplifies the configuration of Spring applications through the automatic assembly mechanism. It takes advantage of Spring's dependency injection (DI) function, allowing developers to quickly build a fully functional application through automatic configuration and conditional annotations. The following are the main ways Spring Boot implements automatic assembly:

1. Java-based configuration:

• Use the @Configuration annotation to mark the configuration class.
• Use @Bean annotation on the method to indicate that the method will return an object, which should be registered as a bean in the Spring application context.

2. Automatic configuration:

• Spring Boot automatically configures most beans based on the jar dependencies in the project. For example, if a dependency on the H2 database is added to the project, Spring Boot will automatically configure an in-memory database.
• Automatic configuration can be enabled through the @EnableAutoConfiguration annotation.

3. Conditional annotations:

• Spring Boot uses conditional annotations, such as @ConditionalOnClass, @ConditionalOnProperty, etc. These annotations allow beans to be used only when It is created and registered only when certain conditions are met.

4. Automatic assembly:

• Use @Autowired, @Resource, @Qualifier and other annotations to implement automatic assembly. Among them, @Autowired is the most commonly used, and it can match by type, name or constructor.
• If there are multiple beans of the same type, you can use the @Qualifier annotation to specify the bean to be injected.

5. Spring Boot Starter:

• In order to simplify the configuration of specific technologies, such as database connections, messaging, etc., Spring Boot provides various Kind of starter dependency. For example, after adding Spring Boot Starter Data JPA, Spring Boot will automatically configure the data source and JPA-related beans.

6. Automatic assembly of third-party libraries:

• Some third-party libraries, such as Thymeleaf, Freemarker, etc., are well integrated with Spring Boot. Can be assembled and used automatically.

7. Customized automatic assembly:

• If the default automatic assembly strategy cannot meet the needs, developers can customize an automatic assembly strategy . This usually involves implementing the ApplicationContextAware interface or overriding the BeanFactory's getBean() method.

8. Component scanning:

• Use the @ComponentScan annotation to tell Spring Boot to scan the specified package to find components, configurations and namespaces. This allows developers to organize components into corresponding packages without having to list all components in the main configuration class.

9. Externalized configuration and property-driven configuration:

Using externalized configuration (such as application.properties), you can easily configure in different environments Use different configuration values ​​or enable/disable certain features. For example, by setting a certain property to a different value, you can control whether a certain bean is created or whether a certain function is enabled.

10. Event-driven automatic assembly: Spring container publishes many events, such as ContextRefreshedEvent, etc. Beans that listen to these events can implement automatic assembly. By listening to these events, some specific functions or initialization logic can be implemented.

11. Spring Boot starter POMs: These are special POMs used to simplify dependency management of specific technologies. For example, after adding the spring-boot-starter-web dependency, the required Spring Web and Tomcat dependencies will be automatically introduced. This not only simplifies dependency management, but also ensures version compatibility.

12. Conditional annotations and conditional classes: Using these features in combination, you can decide whether to create a bean or use a specific implementation based on runtime conditions. For example, you can decide whether to create a bean based on whether a class or a property exists in the classpath.

13. Customized BeanPostProcessor and BeanFactoryPostProcessor: By implementing these interfaces, developers can customize the logic for processing the bean life cycle and configuration. For example, the bean definition can be modified or enhanced in a custom BeanPostProcessor.

14. Combination and mixed use: In practical applications, multiple automatic assembly technologies are usually used in combination. For example, both Java-based configuration and annotations are used to define beans, and Spring Boot's automatic configuration function is used to simplify the configuration of specific technologies. This makes the code more concise and clear while maintaining feature richness.

15. Version control and compatibility: Since Spring Boot and its related technologies are constantly updated and evolved, developers need to pay attention to official documents and version update instructions to ensure that the technology used There is good compatibility between versions. This helps avoid problems and unnecessary complexity caused by version mismatches.

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