Spring Annotations are a form of metadata that provides data about a program. Annotations are used to provide supplemental information about a program. It does not have a direct effect on the operation of the code they annotate. It does not change the action of the compiled program.
@Service Annotation
In an application, the business logic resides within the service layer so we use the @Service Annotation to indicate that a class belongs to that layer. It is also a specialization of @Component Annotation like the @Repository Annotation. One most important thing about the @Service Annotation is it can be applied only to classes. It is used to mark the class as a service provider. So overall @Service annotation is used with classes that provide some business functionalities. Spring context will autodetect these classes when annotation-based configuration and classpath scanning is used.
Step By Step Implementation
Step 1: Create a Simple Spring Boot Project
Step 2: Add the spring-context dependency in your pom.xml file. Go to the pom.xml file inside your project and add the following spring-context dependency.
XML
<dependency> <groupId>org.springframework</groupId> <artifactId>spring-context</artifactId> <version>5.3.13</version></dependency> |
Step 3: In your project create one package and name the package as “service”. In the service, the package creates a class and name it as “MyServiceClass”.
Java
// Java Program to Illustrate MyServiceClass// Importing package module to code modulepackage com.example.demo.service;// Importing required classesimport org.springframework.stereotype.Service;// Annotation@Service// Classpublic class MyServiceClass { // Method // To compute factorial public int factorial(int n) { // Base case if (n == 0) return 1; return n * factorial(n - 1); }} |
In this code notice that it’s a simple java class that provides functionalities to calculate the factorial of a number. So we can call it a service provider. We have annotated it with @Service annotation so that spring-context can autodetect it and we can get its instance from the context.
Step 4: Spring Repository Test
So now our Spring Repository is ready, let’s test it out. Go to the DemoApplication.java file and refer to the below code.
Java
// Java Program to Illustrate DemoApplication// Importing package module to code fragmentpackage com.example.demo;// Importing required classesimport com.example.demo.service.MyServiceClass;import org.springframework.boot.autoconfigure.SpringBootApplication;import org.springframework.context.annotation.AnnotationConfigApplicationContext;// Annotation@SpringBootApplication// Main classpublic class DemoApplication { // MAin driver method public static void main(String[] args) { AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(); context.scan("com.example.demo"); context.refresh(); MyServiceClass myServiceClass = context.getBean(MyServiceClass.class); // Testing the factorial method int factorialOf5 = myServiceClass.factorial(5); System.out.println("Factorial of 5 is: " + factorialOf5); // Closing the spring context // using close() method context.close(); }} |
Output:
@Repository Annotation
@Repository Annotation is a specialization of @Component annotation which is used to indicate that the class provides the mechanism for storage, retrieval, update, delete and search operation on objects. Though it is a specialization of @Component annotation, so Spring Repository classes are autodetected by spring framework through classpath scanning. This annotation is a general-purpose stereotype annotation which very close to the DAO pattern where DAO classes are responsible for providing CRUD operations on database tables.
Step By Step Implementation
Step 1: Create a Simple Spring Boot Project
Refer to this article Create and Setup Spring Boot Project in Eclipse IDE and create a simple spring boot project.
Step 2: Add the spring-context dependency in your pom.xml file. Go to the pom.xml file inside your project and add the following spring-context dependency.
XML
<dependency> <groupId>org.springframework</groupId> <artifactId>spring-context</artifactId> <version>5.3.13</version></dependency> |
Step 3: In your project create two packages and name the package as “entity” and “repository”. In the entity, package creates a class name it as Student. In the repository, the package creates a Generic Interface named as DemoRepository and a class name it as StudentRepository.
Step 4: Create an entity class for which we will implement a spring repository. Here our entity class is Student. Below is the code for the Student.java file.
Java
// Java Program to Illustrate Simple POJO (Plain Old Java// Object) Classpackage com.example.demo.entity;// Classpublic class Student { // Attributes private Long id; private String name; private int age; // Generating the constructor public Student(Long id, String name, int age) { this.id = id; this.name = name; this.age = age; } // Getter-setters public Long getId() { return id; } public void setId(Long id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } // Overriding toString() method of String class @Override public String toString() { return "Student{" + "id=" + id + ", name='" + name + '\'' + ", age=" + age + '}'; }} |
Step 5: Before implementing the Repository class we have created a generic DemoRepository interface to provide the contract for our repository class to implement.
Java
// Java Program to illustrate DemoRepository Filepackage com.example.demo.repository;public interface DemoRepository<T> { // Save method public void save(T t); // Find a student by its id public T findStudentById(Long id);} |
Step 6: Now let’s look at our StudentRepository class implementation.
Java
// Java Program to Illustrate StudentRepository Filepackage com.example.demo.repository;import com.example.demo.entity.Student;import org.springframework.stereotype.Repository;import java.util.HashMap;import java.util.Map;@Repositorypublic class StudentRepository implements DemoRepository<Student> { // Using an in-memory Map // to store the object data private Map<Long, Student> repository; public StudentRepository() { this.repository = new HashMap<>(); } // Implementation for save method @Override public void save(Student student) { repository.put(student.getId(), student); } // Implementation for findStudentById method @Override public Student findStudentById(Long id) { return repository.get(id); }} |
In this StudentRepository.java file, you can notice that we have added the @Repository annotation to indicate that the class provides the mechanism for storage, retrieval, update, delete and search operation on objects.
Note: Here we have used an in-memory Map to store the object data, you can use any other mechanisms too. In the real world, we use Databases to store object data.
Step 7: Spring Repository Test
So now our Spring Repository is ready, let’s test it out. Go to the DemoApplication.java file and refer to the below code.
Java
// Java Program to Illustrate Spring Repository Testpackage com.example.demo;import com.example.demo.entity.Student;import com.example.demo.repository.StudentRepository;import org.springframework.boot.autoconfigure.SpringBootApplication;import org.springframework.context.annotation.AnnotationConfigApplicationContext;// Class@SpringBootApplicationpublic class DemoApplication { // Main driver method public static void main(String[] args) { AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(); context.scan("com.example.demo"); context.refresh(); StudentRepository repository = context.getBean(StudentRepository.class); // Testing the store method repository.save(new Student(1L, "Anshul", 25)); repository.save(new Student(2L, "Mayank", 23)); // Testing the retrieve method Student student = repository.findStudentById(1L); System.out.println(student); // Closing the spring context // using standard close() method context.close(); }} |
Output: Lastly, run your application and you should get the following output as shown below as follows:
Difference Between @Service Annotation and @Repository Annotation
|
@Service Annotation |
@Repository Annotation |
|---|---|
| @Service annotation is used with classes that provide some business functionalities. | @Repository Annotation is used to indicate that the class provides the mechanism for storage, retrieval, update, delete and search operation on objects. |
| @Service Annotation is a specialization of @Component Annotation. | @Repository Annotation is also a specialization of @Component Annotation. |
| It can be applied only to classes. | It is used at the class level. |
| It is used to mark the class as a service provider. | It is used to mark the interface as DAO (Data Access Object) provider. |
| It is a Stereotype Annotations. | It is also a Stereotype Annotations. |
