Spring 在使用JPARepository的Spring应用程序中需要的bean

问题描述

我在bean实例化方面遇到了问题。

在table.football.play.service.impl.PlayerServiceImpl的构造函数的参数0中，需要一个类型为'table.football.play.repository.PlayerRepository'的bean，但找不到该bean。

错误

这是我的类

package table.football.play.repository;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;
import table.football.play.entity.Player;

@Repository
public interface PlayerRepository extends JpaRepository<Player,Long> {

}

这是服务的实现:

package table.football.play.service.impl;

import static table.football.play.util.ConvertEntityToDto.convertListPlayerEntityToListPlayerDto;

import java.util.List;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import table.football.play.dto.PlayerDTO;
import table.football.play.entity.Player;
import table.football.play.repository.PlayerRepository;
import table.football.play.service.interf.PlayerService;

@Service
public class PlayerServiceImpl implements PlayerService{

  private PlayerRepository playerRepository;

  @Autowired
  public PlayerServiceImpl(PlayerRepository playerRepository){
    this.playerRepository = playerRepository;
  }

  @Override
  public List<PlayerDTO> findAll(){
    List<Player> listPlayer = playerRepository.findAll();
    List<PlayerDTO> playerDTOList = convertListPlayerEntityToListPlayerDto(listPlayer);
    return playerDTOList;
  }


}

有一个实体类

package table.football.play.entity;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;
import lombok.Data;

@Data
@Entity
@Table(name="players")
public class Player {
  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;

  @Column(name="name")
  private String name;
  @Column(name="surname")
  private String surname;

}

最后这是我的pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>3.1.5</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>table.football</groupId>
    <artifactId>play</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>game</name>
    <description>calcio balilla project</description>
    <properties>
        <java.version>17</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>javax.persistence</groupId>
            <artifactId>javax.persistence-api</artifactId>
            <version>2.2</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.data</groupId>
            <artifactId>spring-data-jpa</artifactId>
            <version>3.1.5</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.postgresql</groupId>
            <artifactId>postgresql</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <version>${project.parent.version}</version>
                <configuration>
                    <excludes>
                        <exclude>
                            <groupId>org.projectlombok</groupId>
                            <artifactId>lombok</artifactId>
                        </exclude>
                    </excludes>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

我尝试在字段上使用@Autowired（这是一种更好的做法？还是在构造函数上使用@Autowired好？还是一样的？）

我读过一些人谈论创建默认构造函数的问题…但是Repository是一个接口，我怎么解决它呢？

有人能解释一下这个错误背后的理论吗？对我来说，仅仅知道它如何工作还不够，我想要理解原理。

解决方案

问题出现在你在Service类中使用的依赖注入（它不起作用，请阅读文档）。

而不是：

private PlayerRepository playerRepository;

  @Autowired
  public PlayerServiceImpl(PlayerRepository playerRepository){
    this.playerRepository = playerRepository;
  }

写字段注入

@Autowired
private PlayerRepository playerRepository;

或者构造器注入：

private final PlayerRepository playerRepository;


  public PlayerServiceImpl(PlayerRepository playerRepository){
    this.playerRepository = playerRepository;
  }

还有第二个问题在这里

<dependency>
            <groupId>javax.persistence</groupId>
            <artifactId>javax.persistence-api</artifactId>
            <version>2.2</version>
        </dependency>

因为你正在使用Spring Boot> 3.x，它使用的是Jakarta.persistence而不是javax，所以只需删除该依赖项并按照下一步操作即可。 修复方法如下：请将以下内容替换为：

<dependency>
            <groupId>org.springframework.data</groupId>
            <artifactId>spring-data-jpa</artifactId>
            <version>3.1.5</version>
        </dependency>

给

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-jpa</artifactId>
    <version>3.1.5</version>
</dependency>

在Entity类中，将所有的javax.导入替换为jakarta.

这将解决问题。