Java 持久化实体管理器工厂返回 null
我正在使用带有 JPA 的 MySql 数据库。我的 persistence.xml 看起来像
<?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="citheph">
<provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
<class>persistence.citheph.pTerm</class>
<class>persistence.citheph.pPublicationterm</class>
<class>persistence.citheph.pPublicationauthor</class>
<class>persistence.citheph.pPublication</class>
<class>persistence.citheph.pCoauthorship</class>
<class>persistence.citheph.pCitation</class>
<class>persistence.citheph.pAuthor</class>
<properties>
<property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/cithepth" />
<property name="javax.persistence.jdbc.password" value="amer1" />
<property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" />
<property name="javax.persistence.jdbc.user" value="root" />
</properties>
</persistence-unit>
</persistence>
在我的 java 代码中，我执行以下
EntityManagerFactory emf = Persistence.createEntityManagerFactory("citheph");
EntityManager em = emf.createEntityManager();
emf 总是返回 null。数据库已连接并且 ping 成功。我什至尝试将持久性单元名称更改为与 persistance.xml 中的条目不匹配的名称，但仍然为空。它没有抛出任何异常。当然，当它到达代码中的第二行时，
EntityManager em = emf.createEntityManager();
我得到一个空指针异常。
任何帮助将不胜感激。
I am using MySql database with JPA. my persistence.xml looks like
<?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="citheph">
<provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
<class>persistence.citheph.pTerm</class>
<class>persistence.citheph.pPublicationterm</class>
<class>persistence.citheph.pPublicationauthor</class>
<class>persistence.citheph.pPublication</class>
<class>persistence.citheph.pCoauthorship</class>
<class>persistence.citheph.pCitation</class>
<class>persistence.citheph.pAuthor</class>
<properties>
<property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/cithepth" />
<property name="javax.persistence.jdbc.password" value="amer1" />
<property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" />
<property name="javax.persistence.jdbc.user" value="root" />
</properties>
</persistence-unit>
</persistence>
in my java code i do the following
EntityManagerFactory emf = Persistence.createEntityManagerFactory("citheph");
EntityManager em = emf.createEntityManager();
emf always come back null. the database is connected and pings successfully. I have even tried to change the persistence-unit name to something that doesn't match the entry in the persistance.xml and I am still getting null. It is not throwing any exceptions. ofcourse when it gets to the second line in the code
EntityManager em = emf.createEntityManager();
I get a null pointer exception.
any help will be greatly appreciated.
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打开最精细的日志记录并确保加载持久性单元时不会发生错误。
您使用的是什么环境，您的类路径上是否有所有必需的 jar ？
Turn logging on finest and ensure no errors are occurring loading the persistence unit.
What environment are you using, do you have all the required jars on your classpath?
您确定 persistence.xml 文件位于 META-INF 文件夹中吗？
Are you sure that the persistence.xml files resides in the META-INF folder?