Question

使用Netbeans开发JavaEE应用程序。实体管理器在应用程序中获取空值。他们没有被注射。仍然会得到一个nullPointerException，因为em在createNamedQuery中得到一个空值。谁能告诉我我错过了什么。

JSP page-index.jsp：

<%@page import="managed.userBean" %>
 <jsp:useBean id="bean" class="managed.userBean" scope="session" />
.....
<input type="submit" value="Submit" onclick="<jsp:scriptlet> bean.validate();</jsp:scriptlet>" />

userBean.java

package managed;

import java.io.Serializable;
import javax.ejb.EJB;
import javax.faces.bean.ManagedBean;
import javax.faces.bean.SessionScoped;
import session.UserFacade;

@ManagedBean
@SessionScoped


public class userBean implements Serializable {

private String uid, password,role,fname,lname;
private String response="" ;
@EJB
UserFacade userFacade;
....
public String validate() {
    System.out.println("in validate going to user facade:  " + uid + password);
    response = userFacade.validateUser(uid,password);
 .....
}

UserFacade.java

package session;
import javax.ejb.EJB;
import javax.ejb.Stateless;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;

@Stateless

public class UserFacade extends AbstractFacade<User> {
@PersistenceContext (unitName = "ExamSysPU")
public EntityManager em;
String role;

@Override
protected EntityManager getEntityManager() {
    System.out.println("check if em is open");
    return em;
}

public UserFacade() {
    super(User.class);
}


    public String validateUser(String uid, String password) {
     ...
              List results = em.createNamedQuery("User.findByUid").setParameter("uid", uid).getResultList();
   ....
}

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="ExamSysPU" transaction-type="JTA">
      <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider> 
     <jta-data-source>test</jta-data-source>
      <exclude-unlisted-classes>false</exclude-unlisted-classes>
      <properties/>
  </persistence-unit>
 </persistence>

谢谢，希尔帕

Answer 1

您的问题是由于您使用UserBean手动创建<jsp:useBean>而不是使用由JSF创建和管理的那个（因此为您自动注入了所有必需的依赖项）。基本上，如果您手动创建和管理bean，那么您还应该手动创建，管理和注入其依赖项。

停止阅读那些已有十年历史的JSP 1.x教程。它们不再适用于这些Java EE 6天了，现在只会让您对正确的方法感到困惑。 JSP已经被Facelets（XHTML）取代。完成一些JSF2 / Facelets教程。基本上，您可以通过至少包含以下内容的Facelets文件替换JSP文件来解决您的具体问题：

<h:form>
    <h:commandButton value="Submit" action="#{bean.validate}" />
</h:form>

另见：

Our JSF wiki page - 包含一个JSF2 / Facelets Hello World启动示例和一些指向健全JSF2教程的链接

Entitymanager抛出NullPointerException

1 个答案:

另见：