Jpa java.lang.ClassNotFoundException:无法加载请求的类：org.postgresql.Driver

我的问题是，当我在Bean中创建DAO实例时

public class ClientDAO {
        EntityManager entity=JPAutil.getEntityManegerFactory().createEntityManager();

    public void create(Client client){
        entity.getTransaction().begin();
        entity.persist(client);
        entity.getTransaction().commit();
        JPAutil.shotDown();
    }
    public void update(Client client){
        entity.getTransaction().begin();
        entity.merge(client);
        entity.getTransaction().commit();
        JPAutil.shotDown();
    }
    public void find(int id){
        entity.getTransaction().begin();
        entity.find(Client.class,id);
    }
    public List<Client> findall(){
            List<Client> listaC= new ArrayList<Client>();
            Query q=entity.createQuery("SELECT c FROM Client c");
            listaC = q.getResultList();
            return listaC;
    }
    public Client findbyId(int idc){
        Client C= new Client();
        Query q=entity.createQuery("SELECT c FROM Client c WHERE id="+idc);
        C = (Client) q.getSingleResult();
        return C;
    }
}

谢谢你抽出时间

xml我已经使测试和本地JPA工作正常。问题是当我尝试在服务器中使用它时。在这个Pom中，有一个驱动程序von Postgres和连接器Hibernate

<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>groupId</groupId>
    <artifactId>pruebe</artifactId>
    <version>1.0-SNAPSHOT</version>

    <!---Servlet-->
    <dependencies>
        <dependency>
            <groupId>javax</groupId>
            <artifactId>javaee-api</artifactId>
            <version>8.0</version>
            <scope>provided</scope>
        </dependency>

        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-entitymanager</artifactId>
            <version>5.4.10.Final</version>
        </dependency>
        <dependency>
            <groupId>postgresql</groupId>
            <artifactId>postgresql</artifactId>
            <version>9.1-901.jdbc4</version>
            <scope>compile</scope>
        </dependency>

    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.5.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>  
</project>```

4.0.0
groupId
普鲁比
1.0-快照
爪哇
JavaEEAPI
8
假如
org.hibernate
休眠实体管理器
5.4.10.最终版本
postgresql
postgresql
9.1-901.jdbc4
编译
org.apache.maven.plugins
maven编译器插件
3.5.1
1.8
1.8
```

您需要将JDBC驱动程序下载到项目中的数据库中，您可以从这里下载

---

您的gradle或pom文件是否具有postresql依赖关系？添加配置文件DataSource大家好谢谢您的回答我的maven中具有依赖关系。我将添加一张关于此的照片=Di在POM依赖项中具有驱动程序。这就是问题所在，问题是当我在Bean中创建DAO实例时。谢谢你的回答=D

<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>groupId</groupId>
    <artifactId>pruebe</artifactId>
    <version>1.0-SNAPSHOT</version>

    <!---Servlet-->
    <dependencies>
        <dependency>
            <groupId>javax</groupId>
            <artifactId>javaee-api</artifactId>
            <version>8.0</version>
            <scope>provided</scope>
        </dependency>

        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-entitymanager</artifactId>
            <version>5.4.10.Final</version>
        </dependency>
        <dependency>
            <groupId>postgresql</groupId>
            <artifactId>postgresql</artifactId>
            <version>9.1-901.jdbc4</version>
            <scope>compile</scope>
        </dependency>

    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.5.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>  
</project>```