HTTP Status 500 - Unable to show problem report: freemarker.core.InvalidReferenceException: The following has evaluated to null or missing: ==> msg [in template "org/apache/struts2/dispatcher/error.ftl" at line 68, column 31] Tip: If the failing expression is known to be legally null/missing, either specify a default value with 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 parenthessis: (myOptionVar.foo)!myDefault, (myOptionVar.foo)?? The failing instruction: ==> ${msg[0]} [in template "org/apache/struts2/dispatcher/error.ftl" at line 68, column 29] Class: freemarker.core.InvalidReferenceException File: InvalidReferenceException.java Method: getInstance Line: 98 - freemarker/core/InvalidReferenceException.java:98:-1

解决办法：在struts.xml 将<constant name="struts.devMode" value="http://www.mamicode.com/true" />

改为<constant name="struts.devMode" value="http://www.mamicode.com/false" />  这只能让你看到你在什么地方出错，具体的错误得你自己解决。

解决 HTTP Status 500 - Unable to show problem report: freemarker.core.InvalidReferenceException: