javax.persistence.PersistenceException：没有名为DogovoraPool的EntityManager的持久性提供程序

Question

我尝试在Eclipse上使用JPA创建GWT应用程序。 但是我得到了这个错误：

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

执行此命令时：

EntityManagerFactory emf = Persistence.createEntityManagerFactory("DogovoraPool");

我把persistence.xml放在了所有地方：

• 工作空间\ gwttest \ SRC \ META-INF \ persistence.xml中;
• 工作空间\ gwttest \战争\ WEB-INF \类\ META-INF \ persistence.xml中;
• 工作空间\ gwttest \战争\ WEB-INF \ lib中\ persistence.xml中。

但它没有帮助:(

的persistence.xml

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0" 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_2_0.xsd">
<persistence-unit name="DogovoraPool" transaction-type="RESOURCE_LOCAL">
<provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
<class>com.val.gwttest.server.entity.Pravform</class>
<properties>
<property name="javax.persistence.jdbc.password" value="xxx" />
<property name="javax.persistence.jdbc.user" value="root" />
<property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" />
<property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/dogovora" />
<property name="eclipselink.logging.level" value="FINE" />
</properties>
</persistence-unit>
</persistence>

请告诉我，如何解决它。