错误：没有EntityManager的持久性提供程序

Question

StackOverflow上已经有很多关于这个错误消息的问题，但我找不到解决方案...

错误是：

严重：映射到响应的异常：500（内部服务器错误）

我的persistence.xml是：

<?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="createJPA" transaction-type="RESOURCE_LOCAL">
<provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
    <class>model.Cumulative</class>
    <class>model.Date</class>
    <class>model.Department</class>
    <class>model.Holiday</class>
    <class>model.Log</class>
    <class>model.Member</class>
    <class>model.Person</class>
    <class>model.Project</class>
    <properties>
        <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/resource_db"/>
        <property name="javax.persistence.jdbc.user" value="root"/>
        <property name="javax. persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>
        <property name="javax.persistence.jdbc.password" value=""/>
    </properties>
</persistence-unit>
</persistence>

它由这行调用（这行没有错误）：

EntityManagerFactory emf = Persistence.createEntityManagerFactory("createJPA", properties);

我的persistence.xml位于Project Explorer中的JPA内容下：

CreateEntityManagerFactory是：

 public static EntityManagerFactory createEntityManagerFactory(String persistenceUnitName, Map properties) {

    EntityManagerFactory emf = null;
    PersistenceProviderResolver resolver = PersistenceProviderResolverHolder.getPersistenceProviderResolver();

    List<PersistenceProvider> providers = resolver.getPersistenceProviders();

    for (PersistenceProvider provider : providers) {
        emf = provider.createEntityManagerFactory(persistenceUnitName, properties);
        if (emf != null) {
            break;
        }
    }
    if (emf == null) {
        throw new PersistenceException("No Persistence provider for EntityManager named " + persistenceUnitName);
    }
    return emf;
}

更新：JPAFactory（在createEntityManagerFactory函数中没有属性值）

package org.odata4j.producer.jpa;

import java.util.Properties;
import java.util.logging.Logger;

import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;

import org.odata4j.producer.ODataProducer;
import org.odata4j.producer.ODataProducerFactory;

public class JPAProducerFactory implements ODataProducerFactory {

  private final Logger log = Logger.getLogger(getClass().getName());

  public static final String PUNAME_PROPNAME = "odata4j.jpa.persistenceUnitName";
  public static final String NAMESPACE_PROPNAME = "odata4j.jpa.edmNamespace";
  public static final String MAX_RESULTS_PROPNAME = "odata4j.jpa.maxResults";

  @Override
   public ODataProducer create(Properties properties) {

  String persistenceUnitName = properties.getProperty(PUNAME_PROPNAME);
    if (persistenceUnitName == null || persistenceUnitName.length() == 0)
      throw new RuntimeException("Missing required property: " + PUNAME_PROPNAME);

    String edmNamespace = properties.getProperty(NAMESPACE_PROPNAME, "");
    String maxResults = properties.getProperty(MAX_RESULTS_PROPNAME, "50");

    log.info(String.format("Using persistence unit [%s] with edm namespace [%s] and max results [%s]", persistenceUnitName, edmNamespace, maxResults));
    log.info("Persistence name is:" + persistenceUnitName);
    EntityManagerFactory emf = Persistence.createEntityManagerFactory("createJPA");
    JPAProducer producer = new JPAProducer(emf, edmNamespace, Integer.parseInt(maxResults));
    return producer;
  }

 }

Answer 1

对于标准JavaSE应用程序，将META-INF\persistence.xml放在src文件夹的根目录中。

如果您使用的是JEE容器托管实体管理器，那么一定要使用JTA作为事务类型，而不是resource_local。然后确保WebContent->META-INF包含persistence.xml。

例如。

<persistence-unit name="createJPA" transaction-type="JTA">
    <jta-data-source>jdbc/MyDatasource</jta-data-source>
</persistence-unit>