没有名为“firstOne”Java 的“EntityManager”的持久性提供程序

Question

我正在使用persistense api连接数据库

这是 pom.xml 依赖项

 <groupId>org.hibernate</groupId>
    <artifactId>hibernate-core</artifactId>
    <version>4.2.8.Final</version>
  </dependency>
  <dependency>
    <groupId>postgresql</groupId>
    <artifactId>postgresql</artifactId>
    <version>9.1-901.jdbc4</version>
  </dependency>
  <dependency>
    <groupId>javax.persistence</groupId>
    <artifactId>persistence-api</artifactId>
    <version>1.0.2</version>

persistense.xml：

<?xml version="1.0" encoding="UTF-8"?>
<persistence 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_1_0.xsd"
    version="1.0">
    <persistence-unit name="firstOne">
         <provider>org.hibernate.ejb.HibernatePersistence</provider>
        <properties>
            <property name="hibernate.ejb.cfgfile" value="/META-INF/hibernate.cfg.xml" />
        </properties>
    </persistence-unit>
</persistence>

hibernate.cfg.xml：

<?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
  <hibernate-configuration>
<session-factory>
    <property name="connection.driver_class">org.postgresql.Driver</property>
    <property name="dialect">org.hibernate.dialect.PostgreSQLDialect</property>
    <property name="hibernate.connection.username">postgres</property>
    <property name="hibernate.connection.password">tauren993</property>
    <property name="hibernate.connection.url">jdbc:postgresql://localhost:5432/hibernate</property>
    <property name="hibernate.hbm2ddl.auto">create</property>
    <property name="hibernate.generate_statistics">false</property>
    <property name="show_sql">true</property>
    <property name="format_sql">true</property>
    <property name="hibernate.cache.use_structured_entries">false</property>
    <property name="hibernate.cache.use_second_level_cache">false</property>

    <mapping class="Employee" />
</session-factory>
</hibernate-configuration>

hibernate.cfg.xml 和 persistense.xml 存储在 project/META-INF 文件夹中，我收到错误

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

堆栈跟踪：

javax.persistence.PersistenceException: No Persistence provider for EntityManager named firstOne
at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:69)
at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:47)
at Main.main(Main.java:14)

Answer 1

在您的持久性单元“firstOne”中，您应该包括提供者。像下面这样说：

<persistence-unit name="firstOne">
  <provider>org.hibernate.ejb.HibernatePersistence</provider>

Answer 2

您可能错过了实体声明。如果您在 JAVA EE 上下文中，请确保您的项目中有一些类被注释为实体。否则，在 JAVA SE 上下文中，您必须按照 thiyaga 所说的方式定义提供者（请参阅 doc）并指定实体如下：

<persistence-unit name="OrderManagement">
    [...]
    <jar-file>MyOrderApp.jar</jar-file>
     or / and 
    <class>com.widgets.Order</class>
    <class>com.widgets.Customer</class>
</persistence-unit>

此外，

如果可以的话，你应该使用 JPA 2

您不再需要hibernate.cfg.xml 文件，只需将您的属性直接放在persitence.xml 文件的<properties> 元素中，确保hibernate 属性以hibernate 为前缀。