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

Question

任何人都可以帮我调试这个错误吗

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.

以下是我的文件：

UserController.java

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);
    }
}

UserService.java

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);
}

UserServiceImpl.java

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);
    }
}

UserDaoImpl.java

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);
    }
}

UserDao.java

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);
}

DemoApplication.java

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);
    }

}

我已经在 DemoApplication.java 中尝试了

@ComponentScan("com.example.demo.service")

，但它不起作用。

我还尝试放置@Autowire并用@Service标记服务。我还检查了所有其他注释，没有发现任何其他遗漏的内容

我希望有一个干净的构建和对 api 的访问

Answer 1

您还没有提供 UserService 实现，Spring 无法将其作为 bean 找到。您有几个选择：

1. 提供 UserService 接口的实现，将

   @Service("UserService")

   注解放在实现类上，并从接口中删除该注解。

2. 将接口更改为具体类并实现方法。

还有其他方法，例如抽象类，但它们往往不常见。

Answer 2

您缺少

UserService

的实现。如果您想保留当前的

@Repository

(

UserDao

) 实现，那么您可以按如下方式重写您的服务：

@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);
}

这应该可以让

UserController

使用。

编辑：

更新后，您的

UserDaoImpl

现在似乎无法自动注入，因为它丢失了

@Autowired

:

@Repository
public class UserDaoImpl implements UserDao {

    private final JdbcTemplate jdbcTemplate;

    @Autowired
    public UserDaoImpl(JdbcTemplate jdbcTemplate) {
        this.jdbcTemplate = jdbcTemplate;
    }