Question

我在Spring Webflow中遇到了奇怪的错误。

2019-06-07 15:04:39.026 ERROR 29470 --- [nio-8096-exec-8] o.a.c.c.C.[.[.[.[dispatcherServlet]      : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is java.lang.NullPointerException] with root cause

java.lang.NullPointerException: null
    at org.springframework.webflow.execution.repository.support.AbstractFlowExecutionRepository.getConversation(AbstractFlowExecutionRepository.java:170) ~[spring-webflow-2.4.4.RELEASE.jar:2.4.4.RELEASE]
    at org.springframework.webflow.execution.repository.support.AbstractFlowExecutionRepository.getLock(AbstractFlowExecutionRepository.java:125) ~[spring-webflow-2.4.4.RELEASE.jar:2.4.4.RELEASE]
    at org.springframework.webflow.executor.FlowExecutorImpl.launchExecution(FlowExecutorImpl.java:142) ~[spring-webflow-2.4.4.RELEASE.jar:2.4.4.RELEASE]
    at org.springframework.webflow.mvc.servlet.FlowHandlerAdapter.handle(FlowHandlerAdapter.java:263) ~[spring-webflow-2.4.4.RELEASE.jar:2.4.4.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:967) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:901) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:872) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:661) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:742) ~[tomcat-embed-core-8.5.23.jar:8.5.23]

这是在spring webflow库内部发生的，我完全不知道为什么。我的流程如下：

<action-state id="checkProductAvailable">
       <evaluate expression="knowledgeSourceService.test(requestParameters.productUUid, requestParameters._eventId)"/>
           <transition on="internet" to="validateAndProceedToSummary">
               <evaluate expression="knowledgeSourceService.extractCustomerSelectedSourceFromRequest(requestParameters)"
                         result="flowScope.customerSelectedSource"/>
               <evaluate expression="knowledgeSourceService.enhanceProductData(requestParameters.productUUid)"
                         result="conversationScope.selectedProduct"/>
           </transition>
           <transition on="requireProducts" to="products" />
   </action-state>


   <decision-state id="validateAndProceedToSummary">
    <if test="knowledgeSourceService.updateCustomerSelection(flowScope.customerSelectedSource, flowScope.productList.selectedProduct.customerSelectedSource)"
        then="proceedToSummary" else="invalidateFormState"/>
</decision-state>

当我从validateAndProceedToSummary切换回products时，它可以正常运行。但是，有了这个validateAndProceedToSummary决策状态，它就失败了。

products处于查看状态：

<view-state id="products" view="invest-flow-products" model="productList">

你能帮我吗？

knowledgeSourceService.updateCustomerSelection(flowScope.customerSelectedSource, flowScope.productList.selectedProduct.customerSelectedSource)

是调用方法：

public boolean updateCustomerSelection(String old, String new) {

但是据我所知，它并没有达到成功路径（proceedToSummary）的此方法（I'put Breakpoint）。它仅在执行失败路径（invalidateFormState）时到达。因此，一些先决条件没有得到满足。但不知道哪个。我们可以以某种方式调试它吗？

Answer 1

如果updateCustomerSelection（）返回的是包装器布尔值，那么我们需要检查是否为null值，因为包装器布尔值也可能也包含null值。

以下代码应解决NPE问题：

if (null != updateCustomerSelection() && updateCustomerSelection()) {
    //code
}

或者如果您正在使用apache commons库，则可以编写如下所示：

if (BooleanUtils.isTrue(updateCustomerSelection())) {
     //code
}

Spring Webflow中的NPE Nullpointer异常

1 个答案: