How to implement a CRUD Rest Service in Spring Boot backed by Relational Database
Tags: java, spring, springboot, restfulws
Published: 2021-02-15 13:30:05

Implementing a Restful WebService in Spring Boot is relatively easier as compared to Core Spring. The framework itself does the heavy lifting, developers need to focus only on the business logic.

Following are the key steps a developer should follow to implement a simple CRUD Rest Service using Spring Boot - 

* Go to the Website [https://start.spring.io] and generate a sample Spring Boot project skeleton.

* pom.xml file should have the following dependencies - 

```
<dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
    </dependencies>
```
* We are using *MySQL database* in this example. Your *application.properties* file in the *src/main/resources* folder should look like following - 

```
spring.datasource.url = jdbc:mysql://localhost:3306/<Database_Name>?useSSL=false
spring.datasource.username = <Your User Name>
spring.datasource.password = <Your Password>


## Hibernate Properties
# The SQL dialect makes Hibernate generate better SQL for the chosen database
spring.jpa.properties.hibernate.dialect = org.hibernate.dialect.MySQL5InnoDBDialect

# Hibernate ddl auto (create, create-drop, validate, update)
spring.jpa.hibernate.ddl-auto = update

```
* Define Entity class which should match the structure of the database table.

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

@Entity
@Table(name = "users")
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;

    @Column(name = "first_name")
    private String firstName;

    @Column(name = "last_name")
    private String lastName;

    @Column(name = "email")
    private String email;

    public User() {

    }

    public User(String firstName, String lastName, String email) {
        super();
        this.firstName = firstName;
        this.lastName = lastName;
        this.email = email;
    }

    public long getId() {
        return id;
    }
    public void setId(long id) {
        this.id = id;
    }
    public String getFirstName() {
        return firstName;
    }
    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }
    public String getLastName() {
        return lastName;
    }
    public void setLastName(String lastName) {
        this.lastName = lastName;
    }
    public String getEmail() {
        return email;
    }
    public void setEmail(String email) {
        this.email = email;
    }
}
```
* Write a *Repository* interface to perform CRUD operations with the database.

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



@Repository
public interface UserRepository extends JpaRepository<User, Long>{

}
```

* Write a custom Exception class while while will be thrown when the Resource can not be found.

```
import org.springframework.http.HttpStatus;
import org.springframework.web.bind.annotation.ResponseStatus;

@ResponseStatus(value = HttpStatus.NOT_FOUND)
public class ResourceNotFoundException extends RuntimeException {

    private static final long serialVersionUID = 1L;

    public ResourceNotFoundException(String message) {
        super(message);
    }
}
```

* Controller class should look like below - 

```
import java.util.List;

import com.pradz.rest.entity.User;
import com.pradz.rest.exception.ResourceNotFoundException;
import com.pradz.rest.repository.UserRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.DeleteMapping;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.PutMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;


@RestController
@RequestMapping("/api/users")
public class UserController {

    @Autowired
    private UserRepository userRepository;

    // get all users
    @GetMapping
    public List <User> getAllUsers() {
        return this.userRepository.findAll();
    }

    // get user by id
    @GetMapping("/{id}")
    public User getUserById(@PathVariable(value = "id") long userId) {
        return this.userRepository.findById(userId)
                .orElseThrow(() -> new ResourceNotFoundException("User not found with id :" + userId));
    }

    // create user
    @PostMapping
    public User createUser(@RequestBody User user) {
        return this.userRepository.save(user);
    }

    // update user
    @PutMapping("/{id}")
    public User updateUser(@RequestBody User user, @PathVariable("id") long userId) {
        User existingUser = this.userRepository.findById(userId)
                .orElseThrow(() -> new ResourceNotFoundException("User not found with id :" + userId));
        existingUser.setFirstName(user.getFirstName());
        existingUser.setLastName(user.getLastName());
        existingUser.setEmail(user.getEmail());
        return this.userRepository.save(existingUser);
    }

    // delete user by id
    @DeleteMapping("/{id}")
    public ResponseEntity <User> deleteUser(@PathVariable("id") long userId) {
        User existingUser = this.userRepository.findById(userId)
                .orElseThrow(() -> new ResourceNotFoundException("User not found with id :" + userId));
        this.userRepository.delete(existingUser);
        return ResponseEntity.ok().build();
    }
}
```
* The entire codebase is available in the below location - 

[https://github.com/pradz13/SpringBootCrudRest.git]

If you want to use some other relational database, use proper database driver dependency and update your application.properties file accordingly.