java bean空指針異常

Question

這是我的第一篇文章，因此希望我能夠達到社區的高標准。

我正在嘗試學習Enterprise Java bean，並且陷入了困境，並要求調試拋出NullPointerException的EAR文件。 這是引發異常的行：

private CrashMonitorTimer crash;
...
/*THE NEXT LINE THROWS THE NULL POINTER EXCEPTION*/
crash.createTimer(Long.parseLong(sCrashMonitorInterval),"CrashMoniterScheduler");

這是被調用的接口的代碼：

import javax.ejb.Local;

@Local
public interface CrashMonitorTimer
{
    public abstract void createTimer(long l, String s);

    public abstract void cancelTimer(String s);
}

這是Java bean的代碼：

@Stateless(name = "CrashMonitorBean", mappedName = "CrashMonitorBean")
@Local(CrashMonitorTimer.class)

public class CrashMonitorBean
    implements CrashMonitorTimer
{

    @Resource
    SessionContext sessionCtx;
    TimerService timerService;
    Timer timer;
    int iMsgCntBeforeCtxRenew;
    int iCtxReusedCount;
    Context _context;
    CrashMonitorInfoUtil crashMonitorRMIContext[];

    public CrashMonitorBean()
    {
        iMsgCntBeforeCtxRenew = 10;
        iCtxReusedCount = 0;
        _context = null;
        crashMonitorRMIContext = null;
    }

    @Override
    public void createTimer(long lInterval, String sName)
    {

        //CrashMonitorInfoUtil leaves context open for reuse 

        System.out.println((new StringBuilder("Creating ")).append(sName).append(" timer").toString());
        timerService = sessionCtx.getTimerService();
        timer = timerService.createTimer(lInterval, lInterval, sName);
        String sPorts = SystemConfigurator.getConfigValue("RMIPorts");
        String saPorts[] = sPorts.split(",");
        String server = SystemConfigurator.getConfigValue("host");
        crashMonitorRMIContext = new CrashMonitorInfoUtil[saPorts.length];
        for(int i = 0; i < saPorts.length; i++)
        {
            crashMonitorRMIContext[i] = new CrashMonitorInfoUtil(server, saPorts[i]);
        }

    }
...
}

我已經對此進行了探討，但是對Java Bean或接口（或新注釋）的使用經驗為零，我什至不知道該嘗試些什么。 任何解釋或指示將不勝感激。

Answer 1

crash變量為null 。

如果sCrashMonitorInterval為null，則將引發NumberFormatException