JPA with TopLink: No META-INF/persistence.xml was

问题:

public class LoginTest {

public static void main(String[] args) {
    EntityManagerFactory emf = Persistence.createEntityManagerFactory("IRCBotPU");
    EntityManager em = emf.createEntityManager();

    em.getTransaction().begin();

    Login lg = new Login();
    lg.setPassword("password");
    lg.setUserName("Rocky");

    em.persist(lg);
    em.flush();

    Login st = em.find(Login.class, lg.getPassword());
    System.out.println(st);

    em.getTransaction().commit();

    em.close();
    emf.close();

}
}

I'm getting an Exception when I try to run this class

javax.persistence.PersistenceException: No Persistence provider for EntityManager named IRCBotPU:  
   No META-INF/persistence.xml was found in classpath.

META-INF/persistence.xml is in my classpath. I don't know what is the reason or this exception.

Persistence library is TopLink.

回答1:

I had the same problem, i was keeping my persistence.xml file in the WebContent/META-INF directory, while the jpa specification says:
the root of the persistence unit is the WEB-INF/classes directory; the persistence.xml file is therefore contained in the WEB-INF/classes/META-INF directory
try placing persistence.xml under src/META-INF.

回答2:

if you are using IntelliJ or a maven project structure you need to place the entire "META-INF/persistence.xml" file in the in resources(src/resources) folder so that it will move your persistence.xml file into "WEB-INF/classes/persistence.xml" location.

if you are using eclipse or something else makes the changes accordingly so that it will move the file to WEB-INF/classes/persistence.xml

anything else did not work for me.

回答3:

The error is somewhat misleading. the XML file itself should not be in the classpath; the part of the message saying "META-INF/persistence.xml" means that the directory containing META-INF/persistence.xml should be.

If your hard drive had the following

C:\libs\JPA\META-INF\Persistence.xml

then your classpath should include this

CLASSPATH=c:\libs\JPA

If META-INF\Persistence.xml were contained in foo.jar, assuming META-INF/Persistence.xml were located on the root folder of the jar, your classpath should have this

CLASSPATH=C:\<path to jar>\foo.jar

This may seem obvious or redundant but my goal is to make sure we're comparing apples to apples and the CLASSPATH, along with classloading, can be a bugger to deal with.

So, can you post your CLASSPATH?

回答4:

persistence.xml should not be in your classpath; JAR file that contains persistence.xml in its META-INF folder should.

回答5:

i have a web application and the following worked fine. What i did was add the META-INF directory with the persistence.xml into the src/main/resources location [Maven project]

回答6:

Your META-INF/persistence.xml file should look something like this:

// <persistence>
//   <persistence-unit name="IRCBotPU">
//     <provider>oracle.toplink.essentials.ejb.cmp3.EntityManagerFactoryProvider</provider>
//     <!-- All persistence classes must be listed -->
//     <class>entity.Customer</class>
//     <class>entity.Order</class>
//     <class>entity.Item</class>
//     <properties>
//       <!-- Provider-specific connection properties -->
//       <property name="toplink.jdbc.driver" value="<database driver>"/>
//       <property name="toplink.jdbc.url" value="<database url>"/>
//       <property name="toplink.jdbc.user" value="<user>"/>
//       <property name="toplink.jdbc.password" value="<password>"/>
//       <!-- Provider-specific settings -->
//       <property name="toplink.logging.level" value="INFO"/>
//     </properties>
//   </persistence-unit>
// </persistence>

Your persistence-unit's name attribute in your persistence.xml doesn't match the value you're passing into the Persistence.createEntityManagerFactory method. Make sure that your persistence-unit name is set to "IRCBotPU".

回答7:

I created a folder callled META-INF under src and it works. "marcosbeirigo" answered it already. I do not know why I have to put that persistance.xml in there though. I put it under WebContent/META-INF and did not work