为什么EntityManager为null？

Question

在我的Web应用程序中，我在Apache
Tomcat（TomEE）/7.0.37服务器上使用OpenJPA。我使用Netbeans自动生成类（“来自数据库的实体类…”和“来自实体类的会话Bean
…”）。在SessionBean（例如UserFacade）上，我想获取EntityManager：

@Stateless
public class UserFacade extends AbstractFacade<User> {
  @PersistenceContext(unitName = "CollDocPU")
  private EntityManager em;

  @Override
  protected EntityManager getEntityManager() {
    return em;
  }
}

但是当我通过上述方式得到它时，我得到的是空值。当我通过：

@Override
protected EntityManager getEntityManager() {
    EntityManagerFactory emf = Persistence.createEntityManagerFactory("CollDocPU");
    EntityManager ecm = emf.createEntityManager(); 
    return ecm;
}

ecm不为空，还可以

我的persistence.xml：

<?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="CollDocPU" transaction-type="RESOURCE_LOCAL">
<provider>org.apache.openjpa.persistence.PersistenceProviderImpl</provider>
<class>model.entity.StudentAddSolution</class>
<class>model.entity.Lecturer</class>
<class>model.entity.Solution</class>
<class>model.entity.Student</class>
<class>model.entity.Course</class>
<class>model.entity.File</class>
<class>model.entity.CourseHasLecturer</class> 
<class>model.entity.Mail</class>
<class>model.entity.StudentAtCourse</class>
<class>model.entity.Roles</class>
<class>model.entity.Task</class>
<class>model.entity.User</class>
<exclude-unlisted-classes>false</exclude-unlisted-classes>
<properties>
   <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:11080/myBase?zeroDateTimeBehavior=convertToNull"/>
   <property name="javax.persistence.jdbc.password" value="pass,"/>
   <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>
   <property name="javax.persistence.jdbc.user" value="myBase"/>
   <property name="openjpa.jdbc.SynchronizeMappings" value="buildSchema(ForeignKeys=true)"/>
  </properties>
 </persistence-unit>
</persistence>

Answer 1

要从中获取不为null的EntityManager

@PersistenceContext(unitName = "CollDocPU")
private EntityManager em;

我必须更改我的persistance.xml，将事务类型更改为“ JTA”并添加：

<jta-data-source>java:openejb/Resource/myDatabase</jta-data-source>
<non-jta-data-source>java:openejb/Resource/myDatabaseUnmanaged</non-jta-data-source>

之后，我必须在服务器配置中声明资源：在[tomee安装文件夹] /conf/tomee.xml文件中：

<?xml version="1.0" encoding="UTF-8"?>
 <tomee>
  <Resource id="myDatabase" type="DataSource">
     JdbcDriver com.mysql.jdbc.Driver
     JdbcUrl jdbc:mysql://localhost:11080/jkitaj?zeroDateTimeBehavior=convertToNull
     UserName jkitaj
     Password pass,
  </Resource>

  <Resource id="myDatabaseUnmanaged" type="DataSource">
     JdbcDriver com.mysql.jdbc.Driver
     JdbcUrl jdbc:mysql://localhost:11080/jkitaj?zeroDateTimeBehavior=convertToNull
     UserName jkitaj
     Password pass,
     JtaManaged false
  </Resource>
 </tomee>

看这里：

http://openejb.979440.n4.nabble.com/org-apache-openjpa-lib-jdbc-
ReportingSQLException-type-not-found-or-user-lacks-privilege-
td4665124.html

http://mobiarch.wordpress.com/2012/12/07/configuring-a-mysql-data-source-in-
tomee/