JPA 与 Maven。无法找到持久性单元

Question

我在与 Maven 一起工作的 JPA 项目上工作，将数据插入到 mysql。 当我运行一个项目时显示错误：

“无法找到持久性单元” 并且数据库不会更新值。

在 mysql 中，我创建了数据库（navin）和表（alien），如下所示：

create database navin

CREATE TABLE alien(
aid int,
aname varchar(255),
atech varchar(255)
)

INSERT INTO alien (aid, aname, atech)
VALUES (3,"darwish","Java");

App.java 类如下：

    package com.telusko.JpaDemo;
    
    import javax.persistence.EntityManager;
    import javax.persistence.EntityManagerFactory;
    import javax.persistence.Persistence;
    
    
    public class App 
    {
        public static void main( String[] args )
        {
            Alien a = new Alien();
            a.setAid(9);
            a.setAname("Maria");
            a.setTech("Hardware");
            
            EntityManagerFactory emf = Persistence.createEntityManagerFactory("pu");
            EntityManager em = emf.createEntityManager();
            
            em.getTransaction().begin();
            em.persist(a);
            em.getTransaction().commit();
            System.out.println(a);
        }
    }

我创建了 Alien Class 如下：

package com.telusko.JpaDemo;

import javax.persistence.Entity;
import javax.persistence.Id;

@Entity
public class Alien 
{
    @Id
    private int aid;
    private String aname;
    private String tech;
    public int getAid() {
        return aid;
    }
    public void setAid(int aid) {
        this.aid = aid;
    }
    public String getAname() {
        return aname;
    }
    public void setAname(String aname) {
        this.aname = aname;
    }
    public String getTech() {
        return tech;
    }
    public void setTech(String tech) {
        this.tech = tech;
    }
    @Override
    public String toString() {
        return "Alien [aid=" + aid + ", aname=" + aname + ", tech=" + tech + "]";
    }
}

persistence.xml 如下：

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.2" xmlns="http://xmlns.jcp.org/xml/ns/persistence" 
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
             xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_2.xsd">
    <persistence-unit name="pu">
    
    <properties>  
        <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>  
        <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/navin?serverTimezone=Australia/Sydney"/>  
        <property name="javax.persistence.jdbc.user" value="root"/>  
        <property name="javax.persistence.jdbc.password" value="1213012"/>  
    </properties>  
    </persistence-unit>
</persistence>

和 pom.xml 如下：

<?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>com.telusko1</groupId>
  <artifactId>jjjjpa</artifactId>
  <version>0.0.1-SNAPSHOT</version>

  <name>jjjjpa</name>
  <!-- FIXME change it to the project's website -->
  <url>http://www.example.com</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven.compiler.source>1.7</maven.compiler.source>
    <maven.compiler.target>1.7</maven.compiler.target>
  </properties>

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.11</version>
      <scope>test</scope>
    </dependency>
    
    <dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-core</artifactId>
    <version>5.2.8.Final</version>
</dependency>
    
    <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>6.0.6</version>
</dependency>
    
  </dependencies>

  <build>
    <pluginManagement><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) -->
      <plugins>
        <!-- clean lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#clean_Lifecycle -->
        <plugin>
          <artifactId>maven-clean-plugin</artifactId>
          <version>3.1.0</version>
        </plugin>
        <!-- default lifecycle, jar packaging: see https://maven.apache.org/ref/current/maven-core/default-bindings.html#Plugin_bindings_for_jar_packaging -->
        <plugin>
          <artifactId>maven-resources-plugin</artifactId>
          <version>3.0.2</version>
        </plugin>
        <plugin>
          <artifactId>maven-compiler-plugin</artifactId>
          <version>3.8.0</version>
        </plugin>
        <plugin>
          <artifactId>maven-surefire-plugin</artifactId>
          <version>2.22.1</version>
        </plugin>
        <plugin>
          <artifactId>maven-jar-plugin</artifactId>
          <version>3.0.2</version>
        </plugin>
        <plugin>
          <artifactId>maven-install-plugin</artifactId>
          <version>2.5.2</version>
        </plugin>
        <plugin>
          <artifactId>maven-deploy-plugin</artifactId>
          <version>2.8.2</version>
        </plugin>
        <!-- site lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#site_Lifecycle -->
        <plugin>
          <artifactId>maven-site-plugin</artifactId>
          <version>3.7.1</version>
        </plugin>
        <plugin>
          <artifactId>maven-project-info-reports-plugin</artifactId>
          <version>3.0.0</version>
        </plugin>
      </plugins>
    </pluginManagement>
  </build>
</project>