Spring Boot @Repository Annotation

🚀 Introduction

The @Repository annotation in Spring Boot is used to define a Data Access Object (DAO) or repository layer that interacts with the database.

✅ Handles database queries automatically
✅ Translates database exceptions into Spring-specific exceptions
✅ Works with JPA, JDBC, and other database technologies

This guide explains how to use @Repository with examples.

1️⃣ What is @Repository?

The @Repository annotation is a specialized version of @Component, meaning Spring will automatically detect and register it as a bean.

It is used to define a class that:
✔ Interacts with a relational database (MySQL, PostgreSQL, etc.)
✔ Performs CRUD operations (Create, Read, Update, Delete)
✔ Works with Spring Data JPA, Hibernate, or JDBC

2️⃣ How @Repository Works with Spring Boot?

✅ Example: Defining a Simple Repository

@Repository
public class UserRepository {
    
    public String getUserById(int id) {
        return "Fetching user with ID: " + id;
    }
}

📌 Spring will detect this class as a bean and allow injection into services.

3️⃣ Using @Repository with Spring Data JPA

Spring Boot simplifies database access using Spring Data JPA, which allows you to define repositories without writing SQL queries.

✅ Example: Creating a JPA Repository

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

@Repository
public interface UserRepository extends JpaRepository<User, Long> {
    
    User findByName(String name); // Custom query method
}

📌 This repository provides built-in CRUD methods like save(), findById(), and deleteById().

4️⃣ @Repository Exception Handling (Automatic Translation)

Spring Boot automatically translates database-related exceptions into Spring’s DataAccessException hierarchy.

✅ Example: Handling Database Errors

@Service
public class UserService {

    @Autowired
    private UserRepository userRepository;

    public void getUserById(Long id) {
        try {
            userRepository.findById(id).orElseThrow(() -> new RuntimeException("User not found"));
        } catch (DataAccessException ex) {
            System.out.println("Database error occurred: " + ex.getMessage());
        }
    }
}

📌 If there is a database error, @Repository converts low-level exceptions into Spring exceptions.

5️⃣ Difference Between @Repository and @Service

Feature	@Repository	@Service
Purpose	Data Access Layer (Database interactions)	Business Logic Layer (Service methods)
Handles Exceptions	Converts database exceptions	Does not handle database exceptions
Spring Component	Yes (@Component specialization)	Yes (@Component specialization)
Example Class	JPA Repository, JDBC DAO	Business logic implementation

6️⃣ When to Use @Repository?

✔ When writing database access logic
✔ When working with Spring Data JPA, Hibernate, or JDBC
✔ When you need automatic exception translation

🚀 Use @Repository for database-related operations and @Service for business logic.

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