Spring Boot启动报错：找不到UserRepository类型的Bean

我不确定为什么会出现这个错误，但怀疑问题出在TestApplication.java里。试过Stack Overflow上相关问题的多种解决方案，还是没找到问题所在。我跟着Amigoscode的视频搭建这个应用，启动时出现如下错误：

错误信息 #

***************************
APPLICATION FAILED TO START
***************************

Description:

Parameter 0 of constructor in com.example.User.UserService required a bean 
of type 'com.example.User.UserRepository' that could not be found.


Action:

Consider defining a bean of type 'com.example.User.UserRepository' in your 
configuration.

项目代码 #

TestApplication.java #

package com.example.test;

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

import com.example.User.UserController;

@SpringBootApplication
@ComponentScan(basePackageClasses = {UserController.class})
public class TestApplication {

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

User.java #

package com.example.User;

import java.time.LocalDate;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.SequenceGenerator;
import javax.persistence.Table;

@Entity
@Table(name = "USER")
public class User {
    @Id
    @SequenceGenerator(
        name = "user_sequence",
        sequenceName = "user_sequence",
        allocationSize = 1
    )
    @GeneratedValue(
        strategy = GenerationType.SEQUENCE,
        generator = "user_sequence"
    )
    private Long id;
    private String PDGA_id;
    private String first_name;
    private String last_name;
    private String email;
    private boolean email_verified;
    private String phone_number;
    private String password;
    private LocalDate created_date;
    private LocalDate modified_date;

    public User(){
    }

    public User(Long id, 
                String PDGA_id, 
                String first_name, 
                String last_name, 
                String email, 
                boolean email_verified, 
                String phone_number, 
                String password, 
                LocalDate created_date, 
                LocalDate modified_date)
    {
        this.id = id;
        this.PDGA_id = PDGA_id;
        this.first_name = first_name;
        this.last_name = last_name;
        this.email = email;
        this.email_verified = email_verified;
        this.phone_number = phone_number;
        this.password = password;
        this.created_date = created_date;
        this.modified_date = modified_date;
    }

    public User(String PDGA_id, 
                String first_name, 
                String last_name, 
                String email, 
                boolean email_verified, 
                String phone_number, 
                String password, 
                LocalDate created_date, 
                LocalDate modified_date)
    {
        this.PDGA_id = PDGA_id;
        this.first_name = first_name;
        this.last_name = last_name;
        this.email = email;
        this.email_verified = email_verified;
        this.phone_number = phone_number;
        this.password = password;
        this.created_date = created_date;
        this.modified_date = modified_date;
    }

    // Getter-Setter
    public Long getId() {
        return this.id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getPDGA_id() {
        return this.PDGA_id;
    }

    public void setPDGA_id(String PDGA_id) {
        this.PDGA_id = PDGA_id;
    }

    public String getFirst_name() {
        return this.first_name;
    }

    public void setFirst_name(String first_name) {
        this.first_name = first_name;
    }

    public String getLast_name() {
        return this.last_name;
    }

    public void setLast_name(String last_name) {
        this.last_name = last_name;
    }

    public String getEmail() {
        return this.email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public boolean isEmail_verified() {
        return this.email_verified;
    }

    public void setEmail_verified(boolean email_verified) {
        this.email_verified = email_verified;
    }

    public String getPhone_number() {
        return this.phone_number;
    }

    public void setPhone_number(String phone_number) {
        this.phone_number = phone_number;
    }

    public String getPassword() {
        return this.password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public LocalDate getCreated_date() {
        return this.created_date;
    }

    public void setCreated_date(LocalDate created_date) {
        this.created_date = created_date;
    }

    public LocalDate getModified_date() {
        return this.modified_date;
    }

    public void setModified_date(LocalDate modified_date) {
        this.modified_date = modified_date;
    }

    @Override
    public String toString(){
        return "User{" +
                "id =" + id +
                ", PDGA_id" + PDGA_id + '\'' +
                ", first_name" + first_name + '\'' + 
                ", last_name" + last_name + '\'' + 
                ", email" + email + '\'' + 
                ", email_verified" + email_verified +
                ", phone_number" + phone_number + '\'' + 
                ", password" + password + '\'' + 
                ", created_date" + created_date +
                ", modified_date" + modified_date +
                "}";
    }
}

UserController.java #

package com.example.User;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping(path = "api/v1/user")
public class UserController {
    
    private final UserService userService;

    @Autowired
    public UserController(UserService userService){
        this.userService = userService;
    }

    @GetMapping()
    public List<User> getUsers(){
        return userService.getUsers();
    }
}

UserRepository.java #

package com.example.User;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

@Repository
public interface UserRepository extends JpaRepository<User, Long> {
}

UserService.java #

package com.example.User;

import org.springframework.stereotype.Service;
import org.springframework.beans.factory.annotation.Autowired;

@Service
public class UserService {

    private final UserRepository userRepository;

    @Autowired
    public UserService(UserRepository userRepository){
        this.userRepository = userRepository;
    }

    public List<User> getUsers(){
        return userRepository.findAll();
    }
}

application.properties #

spring.datasource.url=jdbc:mariadb://localhost:3306/LiensDiGoLinks
spring.datasource.username=root
spring.datasource.password=Password123!
spring.datasource.driver-class-name=org.mariadb.jdbc.Driver

spring.jpa.show-sql=true
spring.jpa.hibernate.ddl-auto=create-drop
spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.MySQL5InnoDBDialect
spring.jpa.properties.hibernate.format_sql=true

问题出在你手动添加的@ComponentScan注解上——它只指定扫描UserController.class，导致Spring找不到UserRepository和UserService，没法创建对应的Bean。

两种解决方法：

1. 直接移除@ComponentScan：@SpringBootApplication本身已经包含组件扫描功能，默认会扫描主类所在包及其子包。修改后的TestApplication.java：

package com.example.test;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class TestApplication {

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

2. 扩展扫描范围：如果必须保留@ComponentScan，要把所有需要扫描的类所在范围加进去，比如直接指定父包com.example：

@ComponentScan(basePackages = {"com.example"})

或者同时包含相关类：

@ComponentScan(basePackageClasses = {UserController.class, UserService.class, UserRepository.class})

优先选第一种方法，最简洁省心。

内容的提问来源于stack exchange，提问作者ImprovedEngineer