我在glassfish中创建了一个服务器，我希望在远程mysql数据库中有一个jpa持久层。
当我尝试使用持久层时，出现以下异常： javax.persistence.PersistenceException: No Persistence provider for EntityManager named em1 基于其他stackoverflow文章，这似乎表明persistence.xml无效。显示my persistence.xml。有人能给我指出正确的方向，让我弄明白如何让这个工作？

<?xml version="1.0" encoding="UTF-8"?>
<persistence xmlns="http://java.sun.com/xml/ns/persistence">
    <persistence-unit name ="em1">
        <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
        <class>data.entry.Movie</class>
        <properties>
            <property name="eclipselink.target-database"
                      value="MySQL4"/>

            <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" />
            <property name="javax.persistence.jdbc.url" value="mysql3.cs.myschool.edu/mydb"/>
            <property name="javax.persistence.jdbc.user" value="mydb" />
            <property name="javax.persistence.jdbc.password" value="mypass" />
        </properties>
    </persistence-unit>
</persistence>