SpringBoot连接MySQL

package com.example.demo.domain;

import java.io.Serializable;

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

@Entity
@Table(name = "user")
public class User implements Serializable {

    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue
    private Long id;
    @Column(name = "username")
    private String userName;
    @Column(name = "password")
    private String passWord;

    public User() {
        super();
    }

    public User(String userName, String p