<!--JPA数据库持久化-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>

$ sudo mysql --password

mysql> create database test; 
-- Creates the new database

mysql> create user 'springuser'@'%' identified by 'ThePassword'; 
-- Creates the user

mysql> grant all on test.* to 'springuser'@'%'; 
-- Gives all privileges to the new user on the newly created database

# change to none after production
spring.jpa.hibernate.ddl-auto=update
spring.datasource.url=jdbc:mysql://${MYSQL_HOST:localhost}:3306/test
spring.datasource.username=user
spring.datasource.password=pwd
spring.datasource.driver-class-name = com.mysql.cj.jdbc.Driver

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
/**
 * @description
 */
@Data
@AllArgsConstructor
@NoArgsConstructor
@Entity
public class User {

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

    @Column(nullable = false, unique = true)
    private String username;
    private String password;
    private String email;

}

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

/**
 * @description
 */
public interface UserRepository extends JpaRepository<User, Long> {

    User findByUsername(String username);
}

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.ResponseBody;

@Controller
@RequestMapping(path="/user")
public class UserController {
    @Autowired
    private UserRepository userRepository;

    @PostMapping(path="/add")
    public @ResponseBody String addNewUser (@RequestParam String name
            , @RequestParam String email) {
        // @ResponseBody means the returned String is the response, not a view name
        // @RequestParam means it is a parameter from the GET or POST request

        User n = new User();
        n.setUsername(name);
        n.setEmail(email);
        userRepository.save(n);
        return "Saved";
    }

    @GetMapping(path="/all")
    public @ResponseBody Iterable<User> getAllUsers() {
        // This returns a JSON or XML with the users
        return userRepository.findAll();
    }
}

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;


@Data
@AllArgsConstructor
@NoArgsConstructor
@Entity
public class Customer {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private Long id;
    private String firstName;
    private String lastName;

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

import java.util.List;

import org.springframework.data.repository.CrudRepository;

public interface CustomerRepository extends CrudRepository<Customer, Long> {

    List<Customer> findByLastName(String lastName);

    Customer findById(long id);
}

import java.util.List;

import org.springframework.data.repository.CrudRepository;

public interface CustomerRepository extends CrudRepository<Customer, Long> {

    List<Customer> findByLastName(String lastName);

    Customer findById(long id);
}