Important Spring learning content: Understand the usage guidelines of common annotations

Necessary for learning Spring: Master the use of common annotations and require specific code examples

Introduction:
Spring framework is currently widely used in Java enterprise-level applications One of the open source frameworks developed. In the process of learning Spring, it is very important to master the use of common annotations. This article will introduce several annotations commonly used in Spring development, and explain their functions and usage in detail with code examples.

1. @Component
@Component is one of the most basic annotations in the Spring framework. It is used to identify a component of a class called Spring. The class identified by the @Component annotation will be automatically scanned by Spring and registered as a bean. The sample code is as follows:

@Component
public class ExampleComponent {

    public void doSomething() {
        // do something
    }
}

2. @Autowired
@Autowired is an annotation used to automatically assemble beans. It can be used on constructors, setter methods, member variables and methods. The sample code is as follows:

@Component
public class ExampleService {

    private ExampleComponent exampleComponent;

    @Autowired
    public ExampleService(ExampleComponent exampleComponent) {
        this.exampleComponent = exampleComponent;
    }

    @Autowired
    public void setExampleComponent(ExampleComponent exampleComponent) {
        this.exampleComponent = exampleComponent;
    }

    @Autowired
    private void init(ExampleComponent exampleComponent) {
        this.exampleComponent = exampleComponent;
    }

    public void useExampleComponent() {
        exampleComponent.doSomething();
    }
}

3. @Configuration
@Configuration is an annotation used to define configuration classes. Classes identified by the @Configuration annotation can use the @Bean annotation to create and configure beans. The sample code is as follows:

@Configuration
public class ExampleConfiguration {

    @Bean
    public ExampleComponent exampleComponent() {
        return new ExampleComponent();
    }

    @Bean
    public ExampleService exampleService() {
        return new ExampleService(exampleComponent());
    }
}

4. @Value
@Value is an annotation used to inject external attribute values. It can be used on member variables, method parameters and methods. The sample code is as follows:

@Component
public class ExampleProperties {

    @Value("${example.property}")
    private String propertyValue;

    @Value("${example.property.default:default-value}")
    private String propertyValueWithDefault;

    public String getPropertyValue() {
        return propertyValue;
    }

    public String getPropertyValueWithDefault() {
        return propertyValueWithDefault;
    }
}

5. @RequestMapping
@RequestMapping is an annotation used to map the request URL. It can be used on controller classes and controller methods. The sample code is as follows:

@RestController
@RequestMapping("/example")
public class ExampleController {

    @RequestMapping(method = RequestMethod.GET)
    public String getExample() {
        return "example";
    }

    @RequestMapping(value = "/{id}", method = RequestMethod.GET)
    public String getExampleById(@PathVariable String id) {
        return "example " + id;
    }
}

6. @Transactional
@Transactional is an annotation used to identify a method or class as a transaction. It can be used on methods, classes and interfaces. The sample code is as follows:

@Service
public class ExampleService {

    @Transactional
    public void doSomething() {
        // do something
    }
}

Summary:
Through the introduction of this article, we have learned how to use several annotations commonly used in Spring development, and demonstrated their specific application scenarios through code examples. Mastering the use of these common annotations is very important for our Spring development. I hope the content of this article will be helpful to you when learning the Spring framework!

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