EJB @PersistenceContext EntityManager抛出NullPointerException [英] EJB @PersistenceContext EntityManager Throws NullPointerException

问题描述

我使用@PersistenceContext注入EntityManager有问题。我尝试用@PersistenceContext在EJB类中注入EntityManager，并且我总是得到NullPointerException。

这里是EJB类：

  @Stateless 
 public class BookEJB {
 
 public BookEJB（）{
 
} 
 
 @PersistenceContext（unitName =BookWebStorePU）
 private EntityManager em; 
 
 public Book createBook（Book book）throws Exception {
 System.out.println（EM：+ em）; 
 em.persist（book）; 
返回书; 
} 
 
 public Book findBookByIsbn10（String isbn10）{
 Book book = new Book（）; 
 em.find（Book.class，isbn10）; 
返回书; 
} 
 //其他方法
} 
  

这里是持久性.xml

 <？xml version =1.0encoding =UTF-8？> 
< persistence version =2.1xmlns =http://xmlns.jcp.org/xml/ns/persistence
 xmlns：xsi =http://www.w3.org/ 2001 / XMLSchema-instance
 xsi：schemaLocation =http://xmlns.jcp.org/xml/ns/persistence 
 http://xmlns.jcp.org/xml/ns/persistence/ persistence_2_1.xsd> 
< persistence-unit name =BookWebStorePUtransaction-type =RESOURCE_LOCAL> 
< provider> org.eclipse.persistence.jpa.PersistenceProvider< / provider> 
< exclude-unlisted-classes> false< / exclude-unlisted-classes> 
< validation-mode> NONE< / validation-mode> 
<属性> 
< property name =javax.persistence.schema-generation.database.actionvalue =create/> 
< property name =javax.persistence.jdbc.drivervalue =org.apache.derby.jdbc.EmbeddedDriver/> 
< property name =javax.persistence.jdbc.urlvalue =jdbc：derby：// localhost：1527 / BookWebStoreDB/> 
< property name =javax.persistence.jdbc.uservalue =bookwebstoreadmin/> 
< property name =javax.persistence.jdbc.passwordvalue =password/> 
<！ - 让EclipseLink自动创建数据库模式 - > 
< property name =eclipselink.ddl-generationvalue =drop-and-create-tables/> 
< property name =eclipselink.ddl-generation.output-modevalue =database/> 
< / properties> 
  

这是我的测试文件：

  public class BookDaoTests {
 
 private BookEJB bookDao; 
私人书籍新书; 
 
 @Before 
 public void init（）{
 
 newBook = new Book（）; 
 newBook.setName（Flying Cow）; 
 newBook.setDescription（超级酷的故事关于飞牛）; 
 newBook.setAuthor（Me）; 
 newBook.setIsbn10（0123456789）; 
 newBook.setIllustrations（true）; 
 newBook.setPublishYear（2013）; 
 newBook.setNumberOfPages（1567）; 
 newBook.setQuantity（58）; 
 
 bookDao = new BookEJB（）; 
 
} 
 
 @Test 
 public void createBook（）throws Exception {
 bookDao.createBook（newBook）; 
 Assert.assertEquals（Book is created！，bookDao.findBookByIsbn10（0123456789），newBook）; 
} 
 
 
} 
  

所以当我运行该测试文件我得到以下错误：

  Testcase：createBook（com.mysite.bookstore.tests.BookDaoTests）：导致错误
 null 
 java.lang.NullPointerException 
在com.mysite.bookwebstore.beans.BookEJB.createBook（BookEJB.java:27）
在com.mysite.bookstore.tests .BookDaoTests.createBook（BookDaoTests.java:46）
 
 EM：null 
  

我使用以下技术：

• Glassfish 4


• JavaEE 7


• JSF


• EclipseLink 2.1


• Java DB

$ b $我希望我们能找到解决这个问题的一些解决方案。我已经解决了这个问题的3天，并从Google和Stackoverflow搜索并测试了解决方案，但没有一个解决方案有所帮助/有效。为了确保EntityManager真的为空，我调试了测试文件，看到它确实给了null。那么我该如何解决这个问题？

解决方案

当EJB部署在容器中时，注入EntityManager实例。
如果您查看生命周期当容器看到@PersistenceContext注释时，它将注入一个容器管理的EntityManager。

问题是在本测试中执行的代码不是由因此，集装箱没有人注入必要的依赖关系。

  bookDao = new BookEJB（）; 
  

当您运行测试时，BookEJB类只是一个简单的POJO，@Stateless和@PersistenceContext注释只是被忽略。

为了测试你的EJB，你有几种方法，看看这个链接。

I'm having a problem with injecting EntityManager by using @PersistenceContext. I try to inject EntityManager in EJB class with @PersistenceContext and I always get NullPointerException.

Here is EJB class:

@Stateless
public class BookEJB {

public BookEJB(){

}

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

public Book createBook(Book book) throws Exception {
    System.out.println("EM: " + em);
    em.persist(book);
    return book;
}

public Book findBookByIsbn10(String isbn10){
    Book book = new Book();
    em.find(Book.class, isbn10);
    return book;
}
//Other methods here
}

Here's Persistence.xml

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.1" xmlns="http://xmlns.jcp.org/xml/ns/persistence" 
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence
http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd">
<persistence-unit name="BookWebStorePU" transaction-type="RESOURCE_LOCAL">
<provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
<exclude-unlisted-classes>false</exclude-unlisted-classes>
<validation-mode>NONE</validation-mode>
<properties>
  <property name="javax.persistence.schema-generation.database.action" value="create"/>
  <property name="javax.persistence.jdbc.driver" value="org.apache.derby.jdbc.EmbeddedDriver"/>
  <property name="javax.persistence.jdbc.url" value="jdbc:derby://localhost:1527/BookWebStoreDB"/>
  <property name="javax.persistence.jdbc.user" value="bookwebstoreadmin"/>
  <property name="javax.persistence.jdbc.password" value="password"/>
  <!-- Let EclipseLink create database schemas automatically -->
  <property name="eclipselink.ddl-generation" value="drop-and-create-tables"/>
  <property name="eclipselink.ddl-generation.output-mode" value="database"/>
</properties>

Here's my test file:

public class BookDaoTests {

private BookEJB bookDao;
private Book newBook;

@Before
public void init() {

    newBook = new Book();      
    newBook.setName("Flying Cow");
    newBook.setDescription("Super cool story about flying cow");
    newBook.setAuthor("Me");
    newBook.setIsbn10("0123456789");
    newBook.setIllustrations(true);
    newBook.setPublishYear(2013);
    newBook.setNumberOfPages(1567);
    newBook.setQuantity(58);

    bookDao = new BookEJB();

}

@Test
public void createBook() throws Exception{
    bookDao.createBook(newBook);
    Assert.assertEquals("Book was created!", bookDao.findBookByIsbn10("0123456789"), newBook);
}


}

So when I run that test file I get following error:

Testcase: createBook(com.mysite.bookstore.tests.BookDaoTests): Caused an ERROR
null
java.lang.NullPointerException
at com.mysite.bookwebstore.beans.BookEJB.createBook(BookEJB.java:27)
at com.mysite.bookstore.tests.BookDaoTests.createBook(BookDaoTests.java:46)

EM: null

I use following technologies:

• Glassfish 4
• JavaEE 7
• JSF
• EclipseLink 2.1
• Java DB

I hope we can find some solution for this problem. I have been tackling now 3 days of this problem and searched and tested solutions from Google and from Stackoverflow but none of the solutions helped/worked. To make sure that the EntityManager was really null, I debugged test file and saw that indeed it gives null. So how can I solve this problem?

解决方案

The EntityManager instance, is injected when the EJB is deployed in the Container. If you take a look at the lifecycle of enterprise bean, you will see clearly when dependency injection occurs. When the Container sees the @Persistencecontext annotation it will inject a container-managed EntityManager.

The problem is that the code executed in this test is not managed by the Container, therefore, no one inject the necessary dependencies.

bookDao = new BookEJB();

When you run the test, the BookEJB class is just a simple POJO, the @Stateless and @PersistenceContext annotations are simply ignored.

You have several alternatives in order to test your EJB, take a look at this link.

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