在开发过程中，我们经常会遇到各种错误和异常。其中一个常见的问题是在使用spring框架的时候，遇到了类似于"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"的错误信息。这个错误提示意味着在userserviceimpl类的构造函数中，第一个参数需要注入一个类型为userdao的bean，但是系统找不到对应的bean。解决这个问题的方法有很多，本文将为大家介绍一种简单有效的解决方案。
问题内容
谁能帮我调试这个错误
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 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 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 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 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 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 中尝试过 @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
错误
解决方法
您缺少 userservice 的实现。如果您想保留 @repository (userdao) 的当前实现，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 getAllUsers();
Long addUser(User user);
void updateUser(User user);
void deleteUser(Long userId);
}
这应该使其可供 usercontroller 使用。
