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我收到此错误：

javax.persistence.PersistenceException: No Persistence provider for EntityManager named MyUnit

但设置应该是正确的。我已经无法理解这个世界了。

它是一个 Maven 项目：

<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/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>MyGroupID</groupId>
<artifactId>MyArtifactID</artifactId>
<packaging>war</packaging>
<version>1.0-SNAPSHOT</version>

<name>MyProject Maven Webapp</name>

<build>
    <finalName>MyProject</finalName>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <configuration>
                <source>1.7</source>
                <target>1.7</target>
            </configuration>
        </plugin>
    </plugins>
</build>

<dependencies>
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>3.8.1</version>
        <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>log4j</groupId>
        <artifactId>log4j</artifactId>
        <version>1.2.17</version>
    </dependency>
    <dependency>
        <groupId>com.h2database</groupId>
        <artifactId>h2</artifactId>
        <version>1.3.168</version>
    </dependency>
    <dependency>
        <groupId>org.hibernate.javax.persistence</groupId>
        <artifactId>hibernate-jpa-2.0-api</artifactId>
        <version>1.0.1.Final</version>
    </dependency>
    <dependency>
        <groupId>org.hibernate</groupId>
        <artifactId>hibernate-entitymanager</artifactId>
        <version>4.2.1.Final</version>
    </dependency>
    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>servlet-api</artifactId>
        <version>2.5</version>
    </dependency>
    <dependency>
        <groupId>org.jdom</groupId>
        <artifactId>jdom2</artifactId>
        <version>2.0.4</version>
    </dependency>
    <dependency>
        <groupId>javax.servlet.jsp</groupId>
        <artifactId>jsp-api</artifactId>
        <version>2.1</version>
    </dependency>
    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>jstl</artifactId>
        <version>1.2</version>
    </dependency>
    <dependency>
        <groupId>jstl</groupId>
        <artifactId>jstl</artifactId>
        <version>1.2</version>
    </dependency>
    <dependency>
        <groupId>taglibs</groupId>
        <artifactId>standard</artifactId>
        <version>1.1.2</version>
    </dependency>
</dependencies>
</project>

我的 persistence.xml 在“src/main/resources/META-INF/persistence.xml”下 可以使用这个 persistence.xml 将数据插入到我的数据库中，所以它肯定存在！

<?xml version="1.0" encoding="UTF-8" ?>
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence
http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd"
version="1.0">

<persistence-unit name="MyUnit" transaction-type="RESOURCE_LOCAL">
    <provider>org.hibernate.ejb.HibernatePersistence</provider>
    <class>sample.beans.MyBean</class>
    <properties>
        <property name="persistence-context.persist-on-commit" value="true"/>
        <property name="hibernate.connection.url" value="jdbc:h2:./data/datastore" />
        <property name="hibernate.dialect" value="org.hibernate.dialect.H2Dialect"></property>
        <property name="hibernate.connection.driver_class" value="org.h2.Driver" />
        <property name="hibernate.connection.password" value="admin" />
        <property name="hibernate.connection.username" value="admin" />
        <property name="hibernate.hbm2ddl.auto" value="update"/>
    </properties>
</persistence-unit>

我尝试在 JSP 中使用它

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<%@page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<jsp:useBean id="my" class="sample.beans.MyBean"></jsp:useBean>

<!DOCTYPE html>
<html>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<head>
<title>Bean Titles</title>
</head>
<body>
<h2>Bean Titles</h2>

<ul>
    <c:forEach var="title" items="${my.titles}">
        <li><c:out value="${title}"/></li>
    </c:forEach>
</ul>

</body>
</html>

正如我已经发布的那样......如果我在我的 glassfish-server 上打开这个 jsp 端，我会收到这个错误：

javax.persistence.PersistenceException: No Persistence provider for EntityManager named MyUnit

这是我打开实体管理器的类：

public class MyBean implements Serializable {

    private List<String> titles = null

    public List<String> getTitles() {
    EntityManagerFactory factory = Persistence.createEntityManagerFactory("MyUnit");
    EntityManager em = factory.createEntityManager();

    Query query = em.createQuery("SELECT title FROM Bla");

    titles = query.getResultList();

    return titles;
}

}

我真的不知道这里有什么问题。我已经在家里的电脑上完成了这个工作。在我的笔记本电脑上（同一个项目！）它不起作用.....

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