Spring @Service Annotation

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In this quick article, we will discuss how to use @Service annotation in Spring (Spring Boot) based applications.

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Spring @Service Annotation Overview

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 the service layer.

Well, @Service annotation serves as a specialization of @Component, allowing for implementation classes to be autodetected through classpath scanning.
 
The 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 is a specialization of @Component as shown below diagram.

Whenever we annotated a class with @Service annotation then Spring Container will automatically create a Spring bean for that class.

Spring @Service Annotation Example

Let's create a simple Spring boot application to bootstrap quickly. Add the below dependencies to your pom.xml file.
<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>

Create User JPA Entity

Let's create a simple User JPA entity that maps with the users table in the database:
@Entity
@Table(name = "users")
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;
    }
}

Create UserRepository

Next, create a UserRepository interface and annotate with @Repository annotation:
@Repository
interface UserRepository extends JpaRepository < User, Integer > {

}
Note Spring Data JPA automatically provides an implementation for the above interface.

Create UserService and UserServiceImpl

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);
    }
}

Testing

Let's write a code to test UserRepository to save user objects into the database table:
@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"));
    }
}

Complete Code

Here is the complete code for your reference:
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 the 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);
    }
}

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