#9 Spring Boot Basics

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Spring Boot is a powerful framework designed to simplify the development of new Spring applications. It reduces the need for extensive configuration by providing a range of non-functional features common to large classes of projects, such as embedded servers, security, and metrics. This article covers the basics of Spring Boot, including how to create your first Spring Boot application, the typical project structure, and commonly used Spring Boot annotations.

Creating Your First Spring Boot Application

Creating a Spring Boot application is straightforward, thanks to the Spring Initializr tool. Here are the steps to create your first Spring Boot application:

  1. Use Spring Initializr:
    • Go to Spring Initializr.
    • Fill in the project metadata (Group, Artifact, Name, Description, Package name).
    • Choose the dependencies you need. For a basic web application, you might select “Spring Web”.
    • Click “Generate” to download the project as a ZIP file.
  2. Import the Project into Your IDE:
    • Extract the ZIP file and open your preferred IDE (IntelliJ IDEA, Eclipse, etc.).
    • Import the project as a Maven or Gradle project.
  3. Run the Application:
    • In the src/main/java directory, find the main application class (annotated with @SpringBootApplication).
    • Right-click the class and select “Run”.
    Main Application Class Example:
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

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

Spring Boot Project Structure

A typical Spring Boot project structure looks like this:

my-spring-boot-app
├── src
│   ├── main
│   │   ├── java
│   │   │   └── com
│   │   │       └── example
│   │   │           └── myapp
│   │   │               └── MySpringBootApplication.java
│   │   ├── resources
│   │       ├── static
│   │       ├── templates
│   │       └── application.properties
│   ├── test
│       ├── java
│           └── com
│               └── example
│                   └── myapp
│                       └── MySpringBootApplicationTests.java
├── mvnw
├── mvnw.cmd
├── pom.xml
└── README.md

Key Directories and Files:

  • src/main/java: Contains the source code of the application.
  • src/main/resources: Contains application resources, such as static files, templates, and properties files.
  • src/test/java: Contains test cases for the application.
  • pom.xml or build.gradle: Build configuration files for Maven or Gradle.
  • application.properties or application.yml: Configuration files for Spring Boot.
Spring Boot Annotations

Spring Boot leverages a variety of annotations to simplify configuration and development. Here are some of the most commonly used annotations:

  1. @SpringBootApplication:
    • This is a convenience annotation that combines @Configuration, @EnableAutoConfiguration, and @ComponentScan.
    • It marks the main class of a Spring Boot application.
    Example:
@SpringBootApplication
public class MySpringBootApplication {
    public static void main(String[] args) {
        SpringApplication.run(MySpringBootApplication.class, args);
    }
}

2. @RestController:

  • This annotation marks a class as a Spring MVC controller, where every method returns a domain object instead of a view.
  • It combines @Controller and @ResponseBody.

Example:

@RestController
public class HelloController {
    @GetMapping("/hello")
    public String hello() {
        return "Hello, Spring Boot!";
    }
}

3. @RequestMapping:

  • Used to map web requests to specific handler classes or handler methods.

Example:

@RestController
@RequestMapping("/api")
public class ApiController {
    @GetMapping("/users")
    public List<User> getUsers() {
        return userService.findAll();
    }
}

4. @Autowired:

  • This annotation is used for automatic dependency injection.

Example:

@Service
public class UserService {
    @Autowired
    private UserRepository userRepository;
}

5. @Entity:

  • Specifies that the class is an entity and is mapped to a database table.

Example:

@Entity
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private String email;
}

6. @Component, @Service, @Repository:

  • These annotations are used to define Spring-managed beans. @Component is a generic stereotype for any Spring-managed component, while @Service and @Repository are specializations for service layer and repository layer beans, respectively.

Example:

@Service
public class MyService {
    public void performService() {
        // service logic
    }
}

Conclusion

Spring Boot simplifies the development of Spring applications by reducing boilerplate code and providing a range of built-in features. By understanding how to create a Spring Boot application, the project structure, and commonly used annotations, you can start building robust and scalable Java applications efficiently. As you dive deeper into Spring Boot, you’ll discover more advanced features that further streamline development and enhance productivity.

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