一个组件需要一个找不到的“javax.persistence.EntityManagerFactory”类型的bean答案

【问题标题】：A component required a bean of type 'javax.persistence.EntityManagerFactory' that could not be found一个组件需要一个找不到的“javax.persistence.EntityManagerFactory”类型的bean
【发布时间】：2020-04-17 06:15:36
【问题描述】：

我刚刚通过教程尝试了 springboot，但是当我运行它时显示错误。我不明白这个错误。

“说明：

com.mii.tugas.Dao.MahasiswaDao 中方法 setEmf 的参数 0 需要一个无法找到的“javax.persistence.EntityManagerFactory”类型的 bean。

行动：

考虑在您的配置中定义一个“javax.persistence.EntityManagerFactory”类型的 bean。”

这是我的 com.mii.tugas.Dao.MahasiswaDao ：

import com.mii.tugas.model.Mahasiswa;
import java.util.List;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import com.mii.tugas.interfaces.MahasiswaServices;

@Service
public class MahasiswaDao implements MahasiswaServices {

    private EntityManagerFactory emf;

    @Autowired
    public void setEmf(EntityManagerFactory emf) {
        this.emf = emf;
    }

    @Override
    public List<Mahasiswa> listMahasiswa() {
        EntityManager em = emf.createEntityManager();
        return em.createQuery("from Data_Mahasiswa", Mahasiswa.class).getResultList();
    }
}

这是我的 MahasiswaServices ：

import com.mii.tugas.model.Mahasiswa;
import java.util.List;

public interface MahasiswaServices {
    List <Mahasiswa> listMahasiswa();
}

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>2.2.2.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.mii</groupId>
    <artifactId>tugas</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>tugas</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <!-- https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter-data-jpa -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-thymeleaf</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>org.eclipse.persistence</groupId>
            <artifactId>eclipselink</artifactId>
            <version>2.5.2</version>
        </dependency>
        <dependency>
            <groupId>org.eclipse.persistence</groupId>
            <artifactId>org.eclipse.persistence.jpa.modelgen.processor</artifactId>
            <version>2.5.2</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-entitymanager</artifactId>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

【问题讨论】：

试试这个@PersistenceUnit EntityManagerFactory emf;
不确定，但您还需要为 JPA 设置 application.properties：参考：spring.io/guides/gs/accessing-data-mysql

标签： java spring-boot spring-data-jpa

【解决方案1】：

您正在混合使用 EclipseLink 和 JPA。先清理一下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>2.2.2.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.mii</groupId>
    <artifactId>tugas</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>tugas</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <!-- https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter-data-jpa -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-thymeleaf</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
           <groupId>org.hibernate</groupId>
           <artifactId>hibernate-jpamodelgen</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

那么你就不需要注入EntityMangerFactory你可以直接注入EntityManager

但你甚至没有EntityManger！

请阅读 Spring Data JPA 的文档：https://docs.spring.io/spring-data/jpa/docs/current/reference/html/#reference

【讨论】：