@Bean annotation example in spring boot

Directory Structure

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
 <modelVersion>4.0.0</modelVersion>
 <parent>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-parent</artifactId>
  <version>3.4.3</version>
  <relativePath/> <!-- lookup parent from repository -->
 </parent>
 <groupId>com.example</groupId>
 <artifactId>BeanExample</artifactId>
 <version>0.0.1-SNAPSHOT</version>
 <name>BeanExample</name>
 <description>Demo project for Spring Boot</description>
 <url/>
 <licenses>
  <license/>
 </licenses>
 <developers>
  <developer/>
 </developers>
 <scm>
  <connection/>
  <developerConnection/>
  <tag/>
  <url/>
 </scm>
 <properties>
  <java.version>17</java.version>
 </properties>
 <dependencies>
  <dependency>
   <groupId>org.springframework.boot</groupId>
   <artifactId>spring-boot-starter-web</artifactId>
  </dependency>

  <dependency>
   <groupId>org.springframework.boot</groupId>
   <artifactId>spring-boot-starter-test</artifactId>
   <scope>test</scope>
  </dependency>
 </dependencies>

 <build>
  <plugins>
   <plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
   </plugin>
  </plugins>
 </build>

</project>

📌 @bean Annotation Example in Spring Boot
The @bean annotation in Spring Boot is used to define a bean manually inside a @Configuration class. It tells Spring to manage an instance of the object and inject it wherever needed.

🔹 Example 1: Basic @bean Usage

✔ Scenario: You want to create and manage a HelloService bean manually instead of using @Component.

🚀 Implementation
Step 1: Create a Service Class

public class HelloService {
    public String sayHello() {
        return "Hello, Spring Boot!";
    }
}

Step 2: Define Bean in a @Configuration Class

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class AppConfig {

    @Bean
    public HelloService helloService() {
        return new HelloService();
    }
}

Step 3: Use the Bean in a Controller

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping("/hello")
public class HelloController {

    private final HelloService helloService;

    public HelloController(HelloService helloService) {
        this.helloService = helloService;
    }

    @GetMapping
    public String sayHello() {
        return helloService.sayHello();
    }
}

🌟 Expected Output

GET /hello  --> Response: "Hello, Spring Boot!"

🛠 When to Use @bean?
✅ When you need fine-grained control over bean creation.
✅ When the class does not use @Component, @Service, or @Repository.
✅ When you want to configure third-party libraries (e.g., RestTemplate, DataSource).