javax.faces.el.E​​valuationException：空长值上的java.lang.NullPointerException

Question

我已经在JSF 1.2 / Rich Faces 3.3 / Tomcat 6 / Java 1.6中开发了应用程序。 在页面中，我有一个用于输入长值的文本框。 如果我将文本框留空并按如下所示在bean中检查其值，则：

  if(this.employeeAge.toString() == "" || this.employeeAge == null ||    
  this.employeeAge  == 0)  // this is code line no 809 generating error
  { System.out.println("employee age not entered");
  }

jsp页面的摘要如下：

   <h:outputText value="Employee Age" />
   <h:inputText value="#{employeeBean.employeeAge}" id="empAge" maxlength="3"  />

这适用于apache tomcat，但在Web Sphere上，出现以下错误

        [12/16/14 12:22:10:641 PKT] 00000037 webapp        E com.ibm.ws.webcontainer.webapp.WebApp logServletError SRVE0293E: [Servlet Error]-[Faces Servlet]: javax
    .faces.FacesException: #{employeeBean.save}: java.lang.NullPointerException
    at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:118)
    at javax.faces.component.UICommand.broadcast(UICommand.java:387)
    at org.ajax4jsf.component.AjaxActionComponent.broadcast(AjaxActionComponent.java:55)
    at org.ajax4jsf.component.AjaxViewRoot.processEvents(AjaxViewRoot.java:324)
    at org.ajax4jsf.component.AjaxViewRoot.broadcastEvents(AjaxViewRoot.java:299)
    at org.ajax4jsf.component.AjaxViewRoot.processPhase(AjaxViewRoot.java:256)
    at org.ajax4jsf.component.AjaxViewRoot.processApplication(AjaxViewRoot.java:469)
    at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:82)
    at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:100)
    at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:265)
    at com.ibm.ws.webcontainer.servlet.ServletWrapper.service(ServletWrapper.java:1657)
    at com.ibm.ws.webcontainer.servlet.ServletWrapper.service(ServletWrapper.java:1597)
    at com.ibm.ws.webcontainer.filter.WebAppFilterChain.doFilter(WebAppFilterChain.java:131)
    at org.ajax4jsf.webapp.BaseXMLFilter.doXmlFilter(BaseXMLFilter.java:178)
    at org.ajax4jsf.webapp.BaseFilter.handleRequest(BaseFilter.java:290)
    at org.ajax4jsf.webapp.BaseFilter.processUploadsAndHandleRequest(BaseFilter.java:388)
    at org.ajax4jsf.webapp.BaseFilter.doFilter(BaseFilter.java:515)
    at com.ibm.ws.webcontainer.filter.FilterInstanceWrapper.doFilter(FilterInstanceWrapper.java:188)
    at com.ibm.ws.webcontainer.filter.WebAppFilterChain.doFilter(WebAppFilterChain.java:116)
    at restricted.AuthorizationFilter.doFilter(AuthorizationFilter.java:162)
    at com.ibm.ws.webcontainer.filter.FilterInstanceWrapper.doFilter(FilterInstanceWrapper.java:188)
    at com.ibm.ws.webcontainer.filter.WebAppFilterChain.doFilter(WebAppFilterChain.java:116)
    at com.ibm.ws.webcontainer.filter.WebAppFilterChain._doFilter(WebAppFilterChain.java:77)
    at com.ibm.ws.webcontainer.filter.WebAppFilterManager.doFilter(WebAppFilterManager.java:908)
    at com.ibm.ws.webcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:934)
    at com.ibm.ws.webcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:502)
    at com.ibm.ws.webcontainer.servlet.ServletWrapperImpl.handleRequest(ServletWrapperImpl.java:179)
    at com.ibm.ws.webcontainer.webapp.WebApp.handleRequest(WebApp.java:3826)
    at com.ibm.ws.webcontainer.webapp.WebGroup.handleRequest(WebGroup.java:276)
    at com.ibm.ws.webcontainer.WebContainer.handleRequest(WebContainer.java:931)
    at com.ibm.ws.webcontainer.WSWebContainer.handleRequest(WSWebContainer.java:1583)
    at com.ibm.ws.webcontainer.channel.WCChannelLink.ready(WCChannelLink.java:186)
    at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.handleDiscrimination(HttpInboundLink.java:445)
    at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.handleNewRequest(HttpInboundLink.java:504)
    at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.processRequest(HttpInboundLink.java:301)
    at com.ibm.ws.http.channel.inbound.impl.HttpICLReadCallback.complete(HttpICLReadCallback.java:83)
    at com.ibm.ws.tcp.channel.impl.AioReadCompletionListener.futureCompleted(AioReadCompletionListener.java:165)
    at com.ibm.io.async.AbstractAsyncFuture.invokeCallback(AbstractAsyncFuture.java:217)
    at com.ibm.io.async.AsyncChannelFuture.fireCompletionActions(AsyncChannelFuture.java:161)
    at com.ibm.io.async.AsyncFuture.completed(AsyncFuture.java:138)
    at com.ibm.io.async.ResultHandler.complete(ResultHandler.java:204)
    at com.ibm.io.async.ResultHandler.runEventProcessingLoop(ResultHandler.java:775)
    at com.ibm.io.async.ResultHandler$2.run(ResultHandler.java:905)
    at com.ibm.ws.util.ThreadPool$Worker.run(ThreadPool.java:1563)
    Caused by: javax.faces.el.EvaluationException: java.lang.NullPointerException
    at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:102)
    at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:102)
    ... 44 more
   Caused by: java.lang.NullPointerException
    at mtech.beans.EmployeeBean.save(EmployeeBean.java:809)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:48)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:600)
    at org.apache.el.parser.AstValue.invoke(AstValue.java:159)
    at org.apache.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:276)
    at org.apache.jasper.el.JspMethodExpression.invoke(JspMethodExpression.java:67)
    at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:88)
    ... 45 more

需要采取什么措施来避免此错误。

Answer 1

if(this.employeeAge.toString() == "" || this.employeeAge == null ||    
  this.employeeAge  == 0)  // this is code line no 809 generating erro

你是第一个使用employeeAge值（ toString()并且要检查它是否经过 null 。

在if ，表达式按顺序求值。 而且，它们是短路的（如果您有||且左侧表达式为true ，则不会评估右侧表达式，因为true || anything -> true 。

只需更改订单

if (this.employeeAge == null || this.employeeAge.toString() == "" ||    
  this.employeeAge  == 0)  // this is code line no 809 generating erro

如果employeeAge为null，则第一个表达式将返回true并且其他任何一个都不被求值。