小编Edd*_*ddy的帖子

我对glassfish,JPA等都很陌生,我在设置它时遇到了很多问题.我打算做的是一个带有持久后端的简单RESTful服务.我使用glassfish3作为应用程序服务器,并已使用jersey-library部署了一个简单的REST服务.现在我想通过JPA提供对数据库的访问.Glassfish附带JavaDB/derby和EclipseLink,是吗？所以,我想用那个:-)

我在META-INF中创建了一个persistence.xml:

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="1.0"
    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_1_0.xsd">
  <persistence-unit name="myPU" transaction-type="JTA">
    <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
    <exclude-unlisted-classes>false</exclude-unlisted-classes>
    <properties>
      <property name="javax.persistence.jdbc.driver"   value="org.apache.derby.jdbc.ClientDataSource" /> <!-- org.apache.derby.jdbc.EmbeddedDriver -->
      <property name="javax.persistence.jdbc.url"      value="jdbc:derby://localhost:1527/sample;create=true" />
      <property name="javax.persistence.jdbc.user"     value="APP" />
      <property name="javax.persistence.jdbc.password" value="APP" />
      <property name="eclipselink.ddl-generation"      value="create-tables" />
    </properties>
  </persistence-unit>
</persistence>

然后我在我的资源中创建了一个字段,我想访问/存储som数据:

@PersistenceUnit(unitName = "myPU")
EntityManagerFactory emf;

但"emf"总是NULL :-(

我想我的persistence.xml配置不合适.

如果有人有提示,我做错了,真的很高兴......

谢谢!