[英]Null pointer exception while EJB injection
我用一個無狀態的Ejb編寫了非常簡單的Web應用程序,當我實現接口時,有趣的時刻來了 - ejb依賴注入不起作用:
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類
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,當我解開“implements Simple”時,我得到NullPointerException(在接口中使用@Remote或@Local注釋),另一種情況我得到“axaxaxa!”。 為什么會這樣? 我讀過Ejb類必須實現接口。
我使用TommEEcas Application Server。
通過更改bean變量類型(到接口類型而不是類類型)來解決問題
帶有NullPointerException的版本
private SimpleBean bean;
工作版
private Simple bean;
在排除故障之前,只需嘗試重新啟動容器(即GlassFish,JBoss等)。
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