嘗試初始化 Java 接口時出現 NullPointerException

Question

我在使用 Java 接口時遇到了一些問題。 基本上我有這個ICardApplMgr ，它應該由ISCPCardApplMrg繼承。 我的界面如下：

public interface ISCPCardApplMrg extends ICardApplMgr { }

public interface ICardApplMgr {
    public String getLossCount(String nric, boolean flag, String serialNumber);
}

對於實現 class：

public class SCPCardApplMrgImpl extends BaseApplMgrImpl implements ISCPCardApplMrg {

public SCPCardApplMrgImpl() {
    super();
}    

public String getLossCount(String nric, boolean flag, String serialNumber) { //logic }

}

然后，我得到了這個服務 class ，它將在上面的 MgrImpl class 中調用 function：

@Service("cardApplication")
public class CardApplicationServiceImpl implements CardApplicationService {
    protected ISCPCardApplMrg scpCardMgr;

    public void setScpCardMgr(ISCPCardApplMrg mgr) {
        this.scpCardMgr = mgr;
    }

    public ICardApplMgr getCardAppMgr(String itemCode) {
        ICardApplMgr ret = null;
        if (Constants.SCP_ITEM_CODE.equals(itemCode)) {
            ret = scpCardMgr;
        }
        if (ret == null) {
            log.warn("Null Manager found for itemCode " + itemCode);
        }
        return ret;
    }

    public String getLossCount(String nric, boolean flag, String itemCode, String serialNumber) {
        return getCardAppMgr(itemCode).getLossCount(nric, flag, serialNumber);
    }
}

但是，當我嘗試調用getLossCount()時，在 getCardAppMgr getCardAppMgr() ) 的 function 內部，我得到了NullPointerException 。 錯誤信息如下：

Exception in executing doSCPCardLoss java.lang.NullPointerException
    at sc.appMgt.business.service.impl.CardApplicationServiceImpl.getLossCount(CardApplicationServiceImpl.java:385)
    at sc.appMgt.presentation.controller.SCPCardCardLossController.doSCPCardLoss(SCPCardCardLossController.java:187)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:105)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:879)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:793)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1040)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006)
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:909)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:707)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
    at weblogic.servlet.internal.StubSecurityHelper$ServletServiceAction.run(StubSecurityHelper.java:286)
    at weblogic.servlet.internal.StubSecurityHelper$ServletServiceAction.run(StubSecurityHelper.java:260)
    at weblogic.servlet.internal.StubSecurityHelper.invokeServlet(StubSecurityHelper.java:137)
    at weblogic.servlet.internal.ServletStubImpl.execute(ServletStubImpl.java:350)
    at weblogic.servlet.internal.TailFilter.doFilter(TailFilter.java:25)
    at weblogic.servlet.internal.FilterChainImpl.doFilter(FilterChainImpl.java:78)
    at sc.idms.common.filter.SessionFilter.doFilter(SessionFilter.java:368)
    at weblogic.servlet.internal.FilterChainImpl.doFilter(FilterChainImpl.java:78)
    at weblogic.servlet.internal.WebAppServletContext$ServletInvocationAction.wrapRun(WebAppServletContext.java:3701)
    at weblogic.servlet.internal.WebAppServletContext$ServletInvocationAction.run(WebAppServletContext.java:3667)
    at weblogic.security.acl.internal.AuthenticatedSubject.doAs(AuthenticatedSubject.java:326)
    at weblogic.security.service.SecurityManager.runAsForUserCode(SecurityManager.java:197)
    at weblogic.servlet.provider.WlsSecurityProvider.runAsForUserCode(WlsSecurityProvider.java:203)
    at weblogic.servlet.provider.WlsSubjectHandle.run(WlsSubjectHandle.java:71)
    at weblogic.servlet.internal.WebAppServletContext.doSecuredExecute(WebAppServletContext.java:2443)
    at weblogic.servlet.internal.WebAppServletContext.securedExecute(WebAppServletContext.java:2291)
    at weblogic.servlet.internal.WebAppServletContext.execute(WebAppServletContext.java:2269)
    at weblogic.servlet.internal.ServletRequestImpl.runInternal(ServletRequestImpl.java:1703)
    at weblogic.servlet.internal.ServletRequestImpl.run(ServletRequestImpl.java:1663)
    at weblogic.servlet.provider.ContainerSupportProviderImpl$WlsRequestExecutor.run(ContainerSupportProviderImpl.java:272)
    at weblogic.invocation.ComponentInvocationContextManager._runAs(ComponentInvocationContextManager.java:352)
    at weblogic.invocation.ComponentInvocationContextManager.runAs(ComponentInvocationContextManager.java:337)
    at weblogic.work.LivePartitionUtility.doRunWorkUnderContext(LivePartitionUtility.java:57)
    at weblogic.work.PartitionUtility.runWorkUnderContext(PartitionUtility.java:41)
    at weblogic.work.SelfTuningWorkManagerImpl.runWorkUnderContext(SelfTuningWorkManagerImpl.java:644)
    at weblogic.work.ExecuteThread.execute(ExecuteThread.java:415)
    at weblogic.work.ExecuteThread.run(ExecuteThread.java:355)

關於如何解決這個問題的任何想法？ 謝謝！

Answer 1

我設法解決了它。 這是由於缺少注釋來連接類。 我在以下位置添加了@Autowired：

@Autowired
protected ISCPCardApplMrg scpCardMgr;

然后在 MgrImpl class 本身：

@Component @Qualifier("scpCardMgr")
public class SCPCardApplMrgImpl extends BaseApplMgrImpl implements ISCPCardApplMrg {
  // codes
}