在開發過程中，我們常常會遇到各種錯誤和異常。其中一個常見的問題是在使用Spring框架的時候，遇到了類似於"com.example.demo.service.UserServiceImpl 中建構函數的參數0 需要類型為“com.example.demo.dao.UserDao”的bean"的錯誤訊息。這個錯誤提示意味著在UserServiceImpl類別的建構子中，第一個參數需要注入一個型別為UserDao的bean，但是系統找不到對應的bean。解決這個問題的方法有很多，本文將為大家介紹一個簡單有效的解決方案。
誰能幫我除錯這個錯誤
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);
}
}我在 demoapplication.java 中嘗試過 @componentscan("com.example.demo.service") 但它不起作用。
我還嘗試放置@autowire並用@service標記服務。我還檢查了所有其他註釋，沒有發現任何其他遺漏的內容
我希望有一個乾淨的構建和對 api 的訪問
錯誤
您缺少 userservice 的實作。如果您想要保留 @repository (userdao) 的目前實現，那麼您可以如下重寫您的服務：
@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);
}
這應該使其可供 usercontroller 使用。
以上是com.example.demo.service.UserServiceImpl 中建構函數的參數 0 需要類型為「com.example.demo.dao.UserDao」的 bean的詳細內容。更多資訊請關注PHP中文網其他相關文章！
