<dependencies>
 <dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-web</artifactId>
 </dependency>
 <dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-data-jpa</artifactId>
 </dependency>
 <dependency>
  <groupId>mysql</groupId>
  <artifactId>mysql-connector-java</artifactId>
 </dependency>
</dependencies>

spring.datasource.url = jdbc:mysql://localhost:3306/test
spring.datasource.username = root
spring.datasource.password = root
spring.datasource.driverClassName = com.mysql.jdbc.Driver
# Specify the DBMS
spring.jpa.database = MYSQL
# Show or not log for each sql query
spring.jpa.show-sql = true
# Hibernate ddl auto (create, create-drop, update)
spring.jpa.hibernate.ddl-auto = update
# Naming strategy
spring.jpa.hibernate.naming-strategy = org.hibernate.cfg.ImprovedNamingStrategy

# stripped before adding them to the entity manager)
spring.jpa.properties.hibernate.dialect = org.hibernate.dialect.MySQL5Dialect

@Entity
@Table(name = "users")
public class User {
 // ==============
 // PRIVATE FIELDS
 // ==============
 // An autogenerated id (unique for each user in the db)
 @Id
 @GeneratedValue(strategy = GenerationType.AUTO)
 private long id;
 // The user email
 @NotNull
 private String email;
 // The user name
 @NotNull
 private String name;
 // ==============
 // PUBLIC METHODS
 // ==============
 public User() { }
 public User(long id) {
  this.id = id;
 }
 // Getter and setter methods
 // ...
} // class User

@Transactional
public interface UserDao extends CrudRepository<User, Long> {
 public User findByEmail(String email);
} 

@Controller
public class UserController {
  @RequestMapping("/get-by-email")
  @ResponseBody
  public String getByEmail(String email) {
   String userId;
   User user = userDao.findByEmail(email);
   if (user != null) {
    userId = String.valueOf(user.getId());
    return "The user id is: " + userId;
   }
   return "user " + email + " is not exist.";
  }
 }