我用一个无状态的 Ejb 编写了非常简单的 Web 应用程序，有趣的时刻出现在我实现接口时——ejb 依赖注入不起作用：
web.xml
<?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>
小服务程序类
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!";
}
}
接口
package com;
import javax.ejb.Remote;
//@Local
@Remote
public interface Simple {
String getSomeString();
}
因此，当我取消注释“implements Simple”时，我得到了 NullPointerException（在接口中带有 @Remote 或 @Local 注释），另一种情况下，我得到了“axaxaxa！”。为什么会发生？我读过 Ejb 类必须实现接口。
我使用 TommEEcas 应用服务器。