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我的简单锻炼计划有些问题。我想从线程调用会话 bean，但它变成了 NullPointer 异常！但如果我从主线程调用它，它可以正常运行

这是警告和例外

Warning: C:\Documents andSettings\User\MyDocuments\NetBeansProjects\ThreadCounter\dist\gfdeploy\ThreadCounter does not exist.
Exception in thread "Thread-2" java.lang.NullPointerException
at threadcounter.Main.run(Main.java:14)
at java.lang.Thread.run(Thread.java:744)

这是调用远程会话 bean 的可运行类

package threadcounter;

import javax.ejb.EJB;
import mysessionbean.CounterSessionBeanRemote;

public class Main implements Runnable {
@EJB
private static CounterSessionBeanRemote counterSessionBean;

@Override
public void run() {
 System.out.println("counter : "+counterSessionBean.getCounter());  //NullPointer
  } 
}

这是我的主要功能

package threadcounter;

public  class Ya {

public static void main(String[] args){
Main t1 = new Main();
new Thread(t1).start();
  }

}

这是会话 bean

package mysessionbean;

import java.util.Random;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.ejb.Stateless;

@Stateless
public class CounterSessionBean implements CounterSessionBeanRemote {
private int counter = 0;

@Override
public int getCounter() {
    int temp = counter;
    temp++;
    Random r = new Random();
    try {
    Thread.sleep(r.nextInt(20));
    } catch (InterruptedException ex) {
    Logger.getLogger(CounterSessionBean.class.getName()).log(Level.SEVERE, null, ex);
    }
    counter = temp;
    return counter;
}


}
4

2 回答 2

1

我想通了！我必须在主函数中注入会话 bean 并将会话 bean 交给具有这样的构造函数的线程 

package threadcounter;

import javax.ejb.EJB;
import mysessionbean.CounterSessionBeanRemote;

public class Main implements Runnable {
    @EJB
    private static CounterSessionBeanRemote counterSessionBean;
    Main(CounterSessionBeanRemote x){
        counterSessionBean = x;
    }
   @Override
   public void run() {
   System.out.println("counter : "+counterSessionBean.getCounter());   
   }
}

这是包含主要功能的类

package threadcounter;

import javax.ejb.EJB;
import mysessionbean.CounterSessionBeanRemote;
public  class Ya {
 @EJB
private static CounterSessionBeanRemote counterSessionBean;

  public static void main(String[] args){
  Main t1 = new Main(counterSessionBean);
  new Thread(t1).start();
  Main t2 = new Main(counterSessionBean);
  new Thread(t2).start();
  Main t3 = new Main(counterSessionBean);
  new Thread(t3).start();
  Main t4 = new Main(counterSessionBean);
  new Thread(t4).start();
  }

}
于 2013-11-24T05:11:01.560 回答
1

您不能在像这样的非容器管理类中使用 @EJB 注入 EJB

@EJB
private static CounterSessionBeanRemote counterSessionBean;

你的类应该是一个容器，可以让它工作。否则，您可以使用 jndi 查找来完成

Context jndiContext = new InitialContext();
CounterSessionBeanRemote bean = (CounterSessionBeanRemote ) jndiContext.lookup("....");

另一件事是：为什么要使用 @EJB 注释，然后在构造函数中稍后分配一个值？这样做没有任何意义。

您可能需要至少通读此http://docs.oracle.com/javaee/6/tutorial/doc/gipjf.html#girfl以使您的简单练习做得好。

于 2013-11-24T19:06:16.740 回答