EJB注入时空指针异常

Question

我用一个无状态的Ejb编写了非常简单的Web应用程序,当我实现接口时,有趣的时刻来了 - ejb依赖注入不起作用:

web.xml中

<?xml version="1.0" ?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
         version="3.0">
  <display-name>Archetype Created Web Application</display-name>
    <servlet>
        <servlet-name>simpleController</servlet-name>
        <servlet-class>com.SimpleController</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>simpleController</servlet-name>
        <url-pattern>*.job</url-pattern>
    </servlet-mapping>
</web-app>

Servlet类

package com;
import javax.ejb.EJB;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class SimpleController extends HttpServlet {

    @EJB
    private SimpleBean bean;

    @Override
    protected void doPost (HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.getWriter().println(bean.getSomeString());
    }

    @Override
    protected void doGet (HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }
}

豆

package com;

import javax.ejb.Stateless;

@Stateless
public class SimpleBean /*implements Simple*/ {
    public String getSomeString(){
        return "axaxaxa!";
    }
}

inteface

package com;

import javax.ejb.Remote;

//@Local
@Remote
public interface Simple {
    String getSomeString();
}

因此,当我解开"implements Simple"时,我得到NullPointerException(在接口中使用@Remote或@Local注释),另一种情况我得到"axaxaxa!".为什么会这样？我读过Ejb类必须实现接口.

我使用TommEEcas Application Server.

Answer 1

通过更改bean变量类型(到接口类型而不是类类型)来解决问题

带有NullPointerException的版本

private SimpleBean bean;

工作版

private Simple bean;