[Sping Boot] Build a REST CRUD API with Hibernate

pom.xml:

    <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>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
            <optional>true</optional>
        </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>
        </dependency>
    </dependencies>

The process can be divide into 6 steps:

1. Update db configs in application.properties

2. Create Employee entity

3. Create DAO interface

4. Create DAO implementation

5. Create REST service to use DAO

6. Create REST controller to use DAO

1. application.properties;

spring.datasource.url=jdbc:mysql://localhost:3306/employee_directory?useSSL=false
spring.datasource.username=root
spring.datasource.password=admin

2. Create Employee entity: Entity is defination of the database table

entity/Employee:

package com.luv2code.springboot.cruddemo.entity;

import javax.persistence.*;

@Entity
@Table(name = "employee")
public class Employee {
    // define fields
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="id")
    private int id;

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

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

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

    public Employee () {

    }

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

    // define getter/setter

    public int getId() {
        return id;
    }

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

    public java.lang.String getFirstName() {
        return firstName;
    }

    public void setFirstName(java.lang.String firstName) {
        this.firstName = firstName;
    }

    public java.lang.String getLastName() {
        return lastName;
    }

    public void setLastName(java.lang.String lastName) {
        this.lastName = lastName;
    }

    public java.lang.String getEmail() {
        return email;
    }

    public void setEmail(java.lang.String email) {
        this.email = email;
    }

    // define tostring
    @Override
    public String toString() {
        return "Employee{" +
                "id=" + id +
                ", firstName=" + firstName +
                ", lastName=" + lastName +
                ", email=" + email +
                '}';
    }
}

3. DAO interface: Opreations of the database, which will be implementated by the service:

dao/EmployeeDAO:

package com.luv2code.springboot.cruddemo.dao;

import com.luv2code.springboot.cruddemo.entity.Employee;
import java.util.List;

public interface EmployeeDAO {
    public List<Employee> findAll();

    public Employee findById (int theId);

    public void save(Employee theEmployee);

    public void deleteById(int theId);
}

4. DAO implementation:

dao/EmployeeDAOHibernateImpl: Here is the implemataion which write query to database

package com.luv2code.springboot.cruddemo.dao;

import java.util.List;
import com.luv2code.springboot.cruddemo.entity.Employee;
import org.hibernate.Session;
import org.hibernate.query.Query;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Repository;

import javax.persistence.EntityManager;
import javax.transaction.Transactional;

@Repository
public class EmployeeDAOHibernateImpl implements EmployeeDAO{

    // define field for entitymanager
    private EntityManager entityManager;

    // setup constructor injection
    @Autowired
    public EmployeeDAOHibernateImpl(EntityManager theEntityManager) {
        entityManager = theEntityManager;
    }

    @Override
    public List<Employee> findAll() {
        // get the current hibernate session
        Session currentSession = entityManager.unwrap(Session.class);

        // create a query
        Query<Employee> theQuery =
                currentSession.createQuery("from Employee", Employee.class);

        // execute query and get result list
        List<Employee> employees = theQuery.getResultList();

        // return the results
        return employees;
    }

    @Override
    public Employee findById(int theId) {
        Session crtSession = entityManager.unwrap(Session.class);
        Employee theEmployee = crtSession.get(Employee.class, theId);

        return theEmployee;
    }

    @Override
    public void save(Employee theEmployee) {
        Session crtSession = entityManager.unwrap(Session.class);
        crtSession.saveOrUpdate(theEmployee);
    }

    @Override
    public void deleteById(int theId) {
        Session crtSession = entityManager.unwrap(Session.class);
        Query theQuery =
                crtSession.createQuery("delete from Employee where id=:employeeId");
        theQuery.setParameter("employeeId", theId);
        theQuery.executeUpdate();
    }
}

5. Create a service to use DAO:

service/EmployeeService:

package com.luv2code.springboot.cruddemo.service;

import com.luv2code.springboot.cruddemo.entity.Employee;

public interface EmployeeService {

    public List<Employee> findAll();

    public Employee findById(int theId);

    public void save (Employee theEmployee);

    public void deleteById(int theId);
}

service/EmployeeServiceImpl:

package com.luv2code.springboot.cruddemo.service;

import com.luv2code.springboot.cruddemo.dao.EmployeeDAO;
import com.luv2code.springboot.cruddemo.entity.Employee;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.transaction.annotation.Transactional;

public class EmployeeServiceImpl implements EmployeeService{

    private EmployeeDAO employeeDAO;

    @Autowired
    public EmployeeServiceImpl (EmployeeDAO theEmployeeDAO) {
        employeeDAO = theEmployeeDAO;
    }

    @Override
    @Transactional
    public List<Employee> findAll() {
        return employeeDAO.findAll();
    }

    @Override
    @Transactional
    public Employee findById(int theId) {
        return employeeDAO.findById(theId);
    }

    @Override
    @Transactional
    public void save(Employee theEmployee) {
        employeeDAO.save(theEmployee);
    }

    @Override
    @Transactional
    public void deleteById(int theId) {
        employeeDAO.deleteById(theId);
    }
}

6. Controller:

rest/EmployeeRestController:

package com.luv2code.springboot.cruddemo.rest;

import com.luv2code.springboot.cruddemo.entity.Employee;
import com.luv2code.springboot.cruddemo.service.EmployeeService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;

@RestController
@RequestMapping("/api")
public class EmployeeRestController {

    private EmployeeService employeeService;

    @Autowired
    public EmployeeRestController (EmployeeService theEmployeeService) {
        employeeService = theEmployeeService;
    }

    // export "/employees" and return list of employees
    @GetMapping("/employees/{employeeId}")
    public List<Employee> findAll () {
        return employeeService.findAll();
    }

    // add mapping for GET /employee/{employeeId}
    public Employee getEmployee (@PathVariable int employeeId) {
        Employee theEmployee = employeeService.findById(employeeId);

        if (theEmployee == null) {
            throw new RuntimeException("Employee id not found - " + employeeId);
        }

        return theEmployee;
    }

    // add mapping for POST /employees - and new employee
    @PostMapping("/employees")
    public Employee addEmployee (@RequestBody Employee theEmployee) {
        // also just in case they pass an id in JSON ... set id to 0
        // this is to force a save of new item ... instead of update

        theEmployee.setId(0);

        // if this is update operation, it will update the id
        employeeService.save(theEmployee);

        return theEmployee;
    }

    // add mapping for PUT /employees - update existing employee
    @PutMapping("/employees")
    public Employee updateEmployee (@RequestBody Employee theEmployee) {
        employeeService.save(theEmployee);

        return theEmployee;
    }

    // delete mapping for DELETE /employees/{employeeId} - delete an existing employee
    @DeleteMapping("/employees/{employeeId}")
    public String deleteEmployee (@PathVariable int employeeId) {
        Employee tempEmployee = employeeService.findById(employeeId);
        if (tempEmployee == null) {
            throw new RuntimeException("Employee id not found - " + employeeId);
        }

        employeeService.deleteById(employeeId);

        return "Deleted employee id - " + employeeId;
    }
}