Spring @Service Annotation

In this quick article, we will discuss how to use @Service annotation in Spring-based applications.
The business logic of an application usually resides within the service layer – so we’ll use the @Service annotation to indicate that a class belongs to that layer:
This annotation serves as a specialization of @Component, allowing for implementation classes to be autodetected through classpath scanning. 
Below diagram shows a source code definition of @Service annotation. Spring context will autodetect these classes when annotation-based configuration and classpath scanning is used because it a specialization of @Component as shown in below diagram.

Spring @Service Annotation Example

Let's create a simple Spring boot application to bootstrap quickly. Add below dependencies to your pom.xml.
<dependency>
 <groupId>org.springframework.boot</groupId>
 <artifactId>spring-boot-starter-web</artifactId>
</dependency>

<dependency>
 <groupId>org.springframework.boot</groupId>
 <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>

Complete Code

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;
import org.springframework.stereotype.Service;

@SpringBootApplication
public class DemoApplication {

    public static void main(String[] args) {
        ConfigurableApplicationContext applicationContext = SpringApplication.run(DemoApplication.class, args);
        UserService userService = (UserService) applicationContext.getBean("userServiceImpl");
        userService.saveUser(new User(10, "Ramesh"));
    }
}

@Entity
@Table
class User {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;
    private String name;

    public User(int id, String name) {
        super();
        this.id = id;
        this.name = name;
    }

    public User() {}

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

@Repository
interface UserRepository extends JpaRepository < User, Integer > {

}

interface UserService {
    public void saveUser(User user);
}

@Service
class UserServiceImpl implements UserService {

    @Autowired
    private UserRepository userRepository;

    @Override
    public void saveUser(User user) {
        userRepository.save(user);
    }
}
Note that we have created ApplicationContext and retrieved bean using getBean() method:
ConfigurableApplicationContext  applicationContext =  SpringApplication.run(DemoApplication.class, args);
UserService userService = (UserService) applicationContext.getBean("userServiceImpl");
userService.saveUser(new User(10, "Ramesh"));

Usage of @Service annotation

interface UserService {
    public void saveUser(User user);
}

@Service
class UserServiceImpl implements UserService {

    @Autowired
    private UserRepository userRepository;

    @Override
    public void saveUser(User user) {
        userRepository.save(user);
    }
}

Related Annotations Posts

  1. Spring Boot Annotations
  2. 15 Spring Core Annotations
  3. Spring Scheduling Annotations
  4. The Spring @Controller and @RestController Annotations with Examples
  5. Spring @RequestBody and @ResponseBody Annotations
  6. Spring @GetMapping, @PostMapping, @PutMapping, @DeleteMapping and @PatchMapping
  7. Spring @Component Annotation Example

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