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 session Bean...”)。在 SessionBean(例如 UserFacade)我想得到 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获取它时，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 不为空并且没问题

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>

最佳答案

从中获取非空 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，我必须在我的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>

看那里:

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/

关于java - 为什么 EntityManager 为空？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/18846709/