注释@Autowired 出现问题。如何决定？

Question

有一段代码：package com.example.sweater3.domain;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.GenerationType;import javax.persistence.Id;@Entitypublic class Message {    @Id    @GeneratedValue(strategy=GenerationType.AUTO)    private Integer id;    private String text;    private String tag;    public Message() {    }    public Message(String text, String tag) {        this.text = text;        this.tag = tag;    }    public void setText(String text) {        this.text = text;    }    public String getText() {        return text;    }    public Integer getId() {        return id;    }    public void setId(Integer id) {        this.id = id;    }    public String getTag() {        return tag;    }    public void setTag(String tag) {        this.tag = tag;    }}_package com.example.sweater3.repos;import com.example.sweater3.domain.Message;import org.springframework.data.repository.CrudRepository;import org.springframework.stereotype.Repository;import java.util.List;@Repositorypublic interface MessageRepo extends CrudRepository<Message, Long> {    List<Message> findByTag(String tag);}__package com.example.sweater3;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;@SpringBootApplicationpublic class Application {    public static void main(String[] args) {        SpringApplication.run(Application.class, args);    }}__package com.example.sweater3;import com.example.sweater3.repos.MessageRepo;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.stereotype.Controller;@Controllerpublic class GreetingController {    @Autowired    private MessageRepo messageRepo;}

Answer 1

您必须在应用程序中启用存储库：

@SpringBootApplication

@EnableJpaRepositories

public class Application {

    public static void main(String[] args) {

        SpringApplication.run(Application.class, args);

    }

}

另请确保添加：

<dependency>

     <groupId>org.springframework.boot</groupId>

     <artifactId>spring-boot-starter-data-jpa</artifactId>       

</dependency>

更新：您必须配置数据库连接和驱动程序。H2 示例（在内存数据库中）

添加新的依赖项：

<dependency>

     <groupId>com.h2database</groupId>

     <artifactId>h2</artifactId>

     <scope>runtime</scope>

</dependency>

在 application.properties 中添加：

spring.datasource.url=jdbc:h2:mem:testdb

spring.datasource.driverClassName=org.h2.Driver

spring.datasource.username=root

spring.datasource.password=root

spring.jpa.database-platform=org.hibernate.dialect.H2Dialect