解决The following has evaluated to null or missing的问题
今天早上遇到了访问页面是，抛出的一个问题
The following has evaluated to null or missing: ==> optionItem[’’+parameters.listValue] [in template “template/haiyisoft/drop/drop.ftl” at line 112, column 58] —- Tip: It’s the final [] step that caused this error, not those before it. —- Tip: If the failing expression is known to legally refer to something that’s sometimes null or missing, either specify a default value like myOptionalVar!myDefault, or use <#if myOptionalVar??>when-present<#else>when-missing</#if>. (These only cover the last step of the expression; to cover the whole expression, use parenthesis: (myOptionalVar.foo)!myDefault, (myOptionalVar.foo)?? —- —- FTL stack trace (“~” means nesting-related): – Failed at: #assign itemValue = optionItem[“” + p… [in template “template/haiyisoft/drop/drop.ftl” at line 112, column 37] —- – Class: freemarker.core.InvalidReferenceException File: InvalidReferenceException.java Method: getInstance Line: 134 – freemarker/core/InvalidReferenceException.java:134:-1
首先我对这个错误进行分析，关键词:
- optionItem[’’+parameters.listValue]
- If the failing expression is known to legally refer to something that’s sometimes null or missing
-
[in template “template/haiyisoft/drop/drop.ftl” at line 112, column 37
看到这里，我一开始因为是前天jsp页面进行赋值是出现了错误，然后通过排查，发现jsp没有问题，然后就把注意力转向了drop.ftl,因为该项目是使用Freemarker模板技术进行赋值的，所以我就打开了drop.ftl文件，查看112行
看完恍然大悟，发现optionItem[’’+parameters.listValue]可能是为null，所以在赋值前需要进行检验，检查该值是否为空的判断
因此我就在112代码中添加了判断
就完美的解决了该问题