add UserEntity.java

import org.apache.shardingsphere.example.common.entity.User;

import javax.persistence.Column;

import javax.persistence.Entity;

import javax.persistence.Id;

import javax.persistence.Table;

@Entity

@Table(name = "t_user")

public final class UserEntity extends User {

    @Id

    @Column(name = "user_id")

    @Override

    public int getUserId() {