java - @EJB 返回 null

Question

我是 JBoss 和 J2EE 的新手。我正在尝试使用会话 bean 联系单例 bean。从长远来看，我想在 Singleton bean 中缓存一些信息，如果它不可用，则在数据库中查找相关信息。但首先，我正在创建最简单的用例。

但是，当我在 Eclipse 中运行这个简单的用例（获取应用程序计数器）时，我得到了对 EJB 的空引用，我不知道下一步该去哪里。

我正在运行 Eclipse Keplar、JDK1.7、JBoss AS 7.1、EJB 3.1

这是jsp文件。

<?xml version="1.0" encoding="ISO-8859-1" ?>
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<jsp:useBean id="counter" class="com.bender.counter.Counter" scope="session"/>
<%-- <jsp:useBean id="counterBean" class="com.bender.counterbean.CounterBean" scope="application"/> --%>

<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" />
<title>Test Counter</title>
</head>

<body>
Hit Counter( <%=counter.getHitCount() %> )<br/>
<%-- Hit CounterBean( <%=counterBean.getHits() %> )<br/> --%>
</body>
</html>

这是第一个会话 bean

package com.bender.counter;

import com.bender.counterbean.CounterBean;
import javax.ejb.EJB;
import javax.enterprise.context.SessionScoped;

@SessionScoped
public class Counter {
    @EJB 
    CounterBean counterBean;

    private int hitCount;

    public Counter() {
        this.hitCount = 0;
    }

    public int getHitCount() {
        if (counterBean == null) {
            System.out.println("Failure");
            hitCount = -1;
        } else {
            hitCount = counterBean.getHits();
        }
        return hitCount;
    }

    public void setHitCount(int newHits) {
        this.hitCount = newHits;
    }
}

这是单例豆

package com.bender.counterbean;

import javax.annotation.PostConstruct;
import javax.ejb.Singleton;
import javax.ejb.Startup;

@Startup
@Singleton
public class CounterBean {
    private int hits = 1;

    public CounterBean() {
        super();
        System.out.println("In constructor of CounterBean.");
    }

    @PostConstruct
    public void init(){
        System.out.format("In post Construct of CounterBean, hits( %d )%n", this.hits);
    }

    // Increment and return the number of hits
    public int getHits() {
        return hits++;
    }
}

这是 server.log 的输出。请注意，counterbean 似乎向 jndi 注册。还要注意 jsp 中的注释。这是从 jsp 联系 CounterBean 的尝试。那次尝试是成功的，所以我认为 CounterBean 在服务器中成功运行。

17:07:50,427 INFO  [org.jboss.as.server.deployment] (MSC service thread 1-12) JBAS015876: Starting deployment of "Counter.war"
17:07:50,443 INFO  [org.jboss.as.ejb3.deployment.processors.EjbJndiBindingsDeploymentUnitProcessor] (MSC service thread 1-15) JNDI bindings for session bean named CounterBean in deployment unit deployment "Counter.war" are as follows:

    java:global/Counter/CounterBean!com.bender.counterbean.CounterBean
    java:app/Counter/CounterBean!com.bender.counterbean.CounterBean
    java:module/CounterBean!com.bender.counterbean.CounterBean
    java:global/Counter/CounterBean
    java:app/Counter/CounterBean
    java:module/CounterBean

17:07:50,458 INFO  [stdout] (MSC service thread 1-8) In constructor of CounterBean.

17:07:50,458 INFO  [stdout] (MSC service thread 1-8) In post Construct of CounterBean, hits( 1 )

17:07:50,474 INFO  [org.jboss.web] (MSC service thread 1-4) JBAS018210: Registering web context: /Counter
17:07:50,489 INFO  [org.jboss.as.server] (management-handler-threads - 83) JBAS018559: Deployed "Counter.war"
17:07:55,185 INFO  [stdout] (http-localhost-127.0.0.1-8080-1) Failure

谢谢你的帮助！

score 1 · Accepted Answer

只有当 DI 容器（在 JBoss 中是焊接）知道该对象时，注入才有效。这通常是因为容器本身创建了实例。您还可以将现有对象传递给容器，让它注入所有依赖项。

看起来 CDI 注入 JSP 页面在 JBoss AS 7 中不起作用：

也许你看看 JSP 的替代方案：

JSF：简短的 JSF 教程
Servlets：Servlet的简短 CDI 注入教程

如果您无法切换到另一种技术，那么您可能必须自己进行注射。使用以下方法让 CDI 容器对给定对象执行所有注入：

public static <T> void programmaticInjection(Class<T> clazz, T injectionObject) throws NamingException {
    InitialContext initialContext = new InitialContext();
    Object lookup = initialContext.lookup("java:comp/BeanManager");
    BeanManager beanManager = (BeanManager) lookup;
    AnnotatedType<T> annotatedType = beanManager.createAnnotatedType(clazz);
    InjectionTarget<T> injectionTarget = beanManager.createInjectionTarget(annotatedType);
    CreationalContext<T> creationalContext = beanManager.createCreationalContext(null);
    injectionTarget.inject(injectionObject, creationalContext);
    creationalContext.release();
}

然后从您的 JSP 调用此方法：

<h3>Inject Test</h3>
          <%
                    MyBean myBean = new MyBean();
                    myBean.programmaticInjection(MyBean.class, myBean);
                    // now call a method on myBean that invokes the injected EJB
          %>
</body>
</html>

MyBean这里是一个简单的 JSF bean，类似于你的：

@Named("myBean")
@SessionScoped
public class MyBean implements Serializable {
    private static final Logger logger = LoggerFactory.getLogger(MyBean.class);
    private static final long serialVersionUID = 1L;
    private long taskId;
    @EJB
    private MyEjb myEjb;

调用programmaticInjection()@EJB 后注解的对象将被注入。

score 0 · Accepted Answer

我能够通过添加 JNDI 查找来解决这个问题。我的 JBoss AS 7.1 实例中必须有一些设置不正确，以便一个 bean 可以使用（默认）JNDI，而 JSP 页面具有（完全）JNDI 访问权限。这是更新（和清理）的代码。

JSP

<?xml version="1.0" encoding="ISO-8859-1" ?>
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<jsp:useBean id="counter" class="com.bender.counter.Counter" scope="session"/>

<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" />
<title>Test Counter</title>
</head>

<body>
Hit Counter( <%=counter.getHitCount() %> )<br/>
</body>
</html>

Session Bean（注意@EJB 被注释掉了）包com.bender.counter；

import com.bender.counterbean.CounterBean;

import javax.ejb.EJB;
import javax.enterprise.context.SessionScoped;
import javax.naming.InitialContext;
import javax.naming.NamingException;

@SessionScoped
public class Counter {
//    @EJB
    private CounterBean counterBean;
    {
        try {
            counterBean = (CounterBean) new InitialContext().lookup("java:global/Counter/CounterBean");
        } catch (NamingException e) { 
            e.printStackTrace();
        }
    }

    private int hitCount;

    public Counter() {
        this.hitCount = 0;
    }

    public int getHitCount() {
        if (counterBean == null) {
            System.out.println("Failure");
            hitCount = -1;
        } else {
            hitCount = counterBean.getHits();
        }
        return hitCount;
    }

    public void setHitCount(int newHits) {
        this.hitCount = newHits;
    }
}

还有单例豆

package com.bender.counterbean;

import javax.annotation.PostConstruct;
import javax.ejb.Singleton;
import javax.ejb.Startup;


@Startup
@Singleton
public class CounterBean {
    private int hits = 1;

    public CounterBean() {
        super();
        System.out.println("In constructor of CounterBean.");
    }

    @PostConstruct
    public void init(){
        System.out.format("In post Construct of CounterBean, hits( %d )%n", this.hits);
    }

    // Increment and return the number of hits
    public int getHits() {
        return hits++;
    }
}

这是 JBoss 控制台输出

16:21:55,740 INFO  [org.jboss.as.server.deployment] (MSC service thread 1-12) JBAS015876: Starting deployment of "Counter.war"
16:21:55,888 INFO  [org.jboss.as.ejb3.deployment.processors.EjbJndiBindingsDeploymentUnitProcessor] (MSC service thread 1-1) JNDI bindings for session bean named CounterBean in deployment unit deployment "Counter.war" are as follows:

    java:global/Counter/CounterBean!com.bender.counterbean.CounterBean
    java:app/Counter/CounterBean!com.bender.counterbean.CounterBean
    java:module/CounterBean!com.bender.counterbean.CounterBean
    java:global/Counter/CounterBean
    java:app/Counter/CounterBean
    java:module/CounterBean

16:21:56,033 INFO  [stdout] (MSC service thread 1-7) In constructor of CounterBean.

16:21:56,033 INFO  [stdout] (MSC service thread 1-7) In post Construct of CounterBean, hits( 1 )

16:21:56,088 INFO  [org.jboss.web] (MSC service thread 1-15) JBAS018210: Registering web context: /Counter
16:21:56,093 INFO  [org.jboss.as] (MSC service thread 1-15) JBAS015874: JBoss AS 7.1.0.Final "Thunder" started in 2001ms - Started 185 of 258 services (72 services are passive or on-demand)
16:21:56,176 INFO  [org.jboss.as.server] (DeploymentScanner-threads - 2) JBAS018559: Deployed "Counter.war"
16:22:11,455 INFO  [stdout] (http-localhost-127.0.0.1-8080-1) In constructor of CounterBean.

java - @EJB 返回 null

2 回答 2

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