Why am I getting NullPointerException in liferay?

问题

I am getting a NullPointerException on the following line:

originalStrutsPortletAction.processAction(
                    originalStrutsPortletAction, portletConfig, actionRequest,
                        actionResponse);

I am printing all the values:

System.out.println(originalStrutsPortletAction);
System.out.println(portletConfig);
System.out.println(actionRequest);
System.out.println(actionResponse);

Output:

com.liferay.portal.struts.StrutsPortletActionAdapter@2f20c4be
com.liferay.portlet.PortletConfigImpl@5f4268dd
com.liferay.portlet.ActionRequestImpl@1054ae1e
com.liferay.portlet.ActionResponseImpl@27733bf2

So why am I getting NullPointerException? Please help.Thanks in advance. The full stack trace is as follows:-

java.lang.NullPointerException
    at com.liferay.portlet.login.action.LoginAction.login(LoginAction.java:196)
    at com.liferay.portlet.login.action.LoginAction.processAction(LoginAction.java:93)
    at com.liferay.portal.struts.StrutsPortletActionAdapter.processAction(StrutsPortletActionAdapter.java:60)
    at com.liferay.portal.kernel.struts.BaseStrutsPortletAction.processAction(BaseStrutsPortletAction.java:44)
    at com.abhishek.ExampleLoginAction.check(ExampleLoginAction.java:185)
    at org.apache.jsp.jsp.otpCheck_jsp._jspService(otpCheck_jsp.java:71)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at com.liferay.portal.kernel.servlet.filters.invoker.InvokerFilterChain.doFilter(InvokerFilterChain.java:116)
    at sun.reflect.GeneratedMethodAccessor503.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at com.liferay.portal.kernel.bean.ClassLoaderBeanHandler.invoke(ClassLoaderBeanHandler.java:67)
    at com.sun.proxy.$Proxy660.doFilter(Unknown Source)
    at com.liferay.portal.kernel.servlet.filters.invoker.InvokerFilterChain.doFilter(InvokerFilterChain.java:116)
    at com.liferay.portal.kernel.servlet.filters.invoker.InvokerFilterChain.processDirectCallFilter(InvokerFilterChain.java:165)
    at com.liferay.portal.kernel.servlet.filters.invoker.InvokerFilterChain.doFilter(InvokerFilterChain.java:96)
    at com.liferay.portal.kernel.servlet.PortalClassLoaderFilter.doFilter(PortalClassLoaderFilter.java:74)
    at com.liferay.portal.kernel.servlet.filters.invoker.InvokerFilterChain.processDoFilter(InvokerFilterChain.java:204)
    at com.liferay.portal.kernel.servlet.filters.invoker.InvokerFilterChain.doFilter(InvokerFilterChain.java:109)
    at com.liferay.portal.kernel.servlet.filters.invoker.InvokerFilter.doFilter(InvokerFilter.java:96)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1023)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

回答1:

Simple answer: You don't get a NullpointerException at that location- at least not according to the stacktrace you post. Liferay's LoginAction does not have an originalStrutsAction. In case you're using 6.2 GA5, this is the code that throws the NullpointerException. Why? That's not what you asked.

Or, to phrase it differently: You're getting a NullpointerException because you dereference a Nullpointer. You'll just need to identify where you actually get it. The stacktrace helps. Who knows what your ExampleLoginAction does before it calls the line that you're posting...

来源：https://stackoverflow.com/questions/39391742/why-am-i-getting-nullpointerexception-in-liferay