com.example.demo.service.UserServiceImpl 中构造函数的参数 0 需要类型为“com.example.demo.dao.UserDao”的 bean

parameter 0 of constructor in com.example.demo.service.userserviceimpl required a 
bean of type 'com.example.demo.dao.userdao' that could not be found.

action:

consider defining a bean of type 'com.example.demo.dao.userdao' in your configuration.

package com.example.demo.controller;

import com.example.demo.model.user;
import com.example.demo.service.userservice;
import org.springframework.beans.factory.annotation.autowired;
import org.springframework.web.bind.annotation.*;

import java.util.list;

@restcontroller
@requestmapping("/api/users")
public class usercontroller {

    @autowired
    private final userservice userservice;
    
    public usercontroller(userservice userservice) {
        this.userservice = userservice;
    }

    @getmapping("/{userid}")
    public user getuserbyid(@pathvariable long userid) {
        return userservice.getuserbyid(userid);
    }

    @getmapping
    public list<user> getallusers() {
        return userservice.getallusers();
    }

    @postmapping
    public long adduser(@requestbody user user) {
        return userservice.adduser(user);
    }

    @putmapping("/{userid}")
    public void updateuser(@pathvariable long userid, @requestbody user user) {
        user.setuserid(userid);
        userservice.updateuser(user);
    }

    @deletemapping("/{userid}")
    public void deleteuser(@pathvariable long userid) {
        userservice.deleteuser(userid);
    }
}

package com.example.demo.service;

import com.example.demo.model.user;
import org.springframework.stereotype.component;
import org.springframework.stereotype.service;

import java.util.list;

public interface userservice {
    user getuserbyid(long userid);

    list<user> getallusers();

    long adduser(user user);

    void updateuser(user user);

    void deleteuser(long userid);
}

package com.example.demo.service;

import com.example.demo.dao.userdao;
import com.example.demo.model.user;
import org.springframework.beans.factory.annotation.autowired;
import org.springframework.stereotype.service;

import java.util.list;

@service
public class userserviceimpl implements userservice {
    
    private final userdao userdao;

    @autowired
    public userserviceimpl(userdao userdao) {
        this.userdao = userdao;
    }

    @override
    public user getuserbyid(long userid) {
        return userdao.getuserbyid(userid);
    }

    @override
    public list<user> getallusers() {
        return userdao.getallusers();
    }

    @override
    public long adduser(user user) {
        return userdao.adduser(user);
    }

    @override
    public void updateuser(user user) {
        userdao.updateuser(user);
    }

    @override
    public void deleteuser(long userid) {
        userdao.deleteuser(userid);
    }
}

package com.example.demo.dao;

import com.example.demo.model.user;
import org.springframework.jdbc.core.beanpropertyrowmapper;
import org.springframework.jdbc.core.jdbctemplate;
import org.springframework.stereotype.repository;

import java.util.list;

@repository
public class userdaoimpl implements userdao {

    private final jdbctemplate jdbctemplate;

    public userdaoimpl(jdbctemplate jdbctemplate) {
        this.jdbctemplate = jdbctemplate;
    }

    @override
    public user getuserbyid(long userid) {
        string sql = "select * from user where user_id = ?";
        return jdbctemplate.queryforobject(sql, new object[]{userid}, new beanpropertyrowmapper<>(user.class));
    }

    @override
    public list<user> getallusers() {
        string sql = "select * from user";
        return jdbctemplate.query(sql, new beanpropertyrowmapper<>(user.class));
    }

    @override
    public long adduser(user user) {
        string sql = "insert into user (first_name, last_name, email, user_avatar_url, podcast_id) " +
                "values (?, ?, ?, ?, ?)";
        jdbctemplate.update(sql, user.getfirstname(), user.getlastname(), user.getemail(),
                user.getuseravatarurl(), user.getpodcastid());

        // retrieve the auto-generated user_id
        return jdbctemplate.queryforobject("select last_insert_id()", long.class);
    }

    @override
    public void updateuser(user user) {
        string sql = "update user set first_name = ?, last_name = ?, email = ?, " +
                "user_avatar_url = ?, podcast_id = ? where user_id = ?";
        jdbctemplate.update(sql, user.getfirstname(), user.getlastname(), user.getemail(),
                user.getuseravatarurl(), user.getpodcastid(), user.getuserid());
    }

    @override
    public void deleteuser(long userid) {
        string sql = "delete from user where user_id = ?";
        jdbctemplate.update(sql, userid);
    }
}

package com.example.demo.dao;
import com.example.demo.model.user;

import java.util.list;

public interface userdao {
    user getuserbyid(long userid);

    list<user> getallusers();

    long adduser(user user);

    void updateuser(user user);

    void deleteuser(long userid);
}

package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.ComponentScan;

@SpringBootApplication
//@ComponentScan("com.example.demo.service")
public class DemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }

}

@Service
public class UserService {

    private final UserDao userDao;

    @Autowired
    public UserService(UserDao userDao) {
        this.userDao = userDao;
    }

    // implement using your DAO
    User getUserById(Long userId);
    List<User> getAllUsers();
    Long addUser(User user);
    void updateUser(User user);
    void deleteUser(Long userId);
}