Why <constant name = "struts. devmode" value = "true"/> is added to struts. xml?

Severe: exception starting filter struts2 Java. lang. nullpointerexception at com. opensymphony. xwork2.util. filemanager $ filerevision. needsreloading (filemanager. java: 209) at com. opensymphony. xwork2.util. filemanager. fileneedsreloading (filemanager. java: 60) at com. opensymphony. xwork2.config. providers. xmlconfigurationprovider. needsreload (xmlconfigurationprovider. java: 325) at Org. apache. struts2.config. strutsxmlconfigurationprovider. needsreload (strutsxmlconfigurationprovider. java: 168) at com. opensymphony. xwork2.config. configurationmanager. conditionalreload (configurationmanager. java: 220) at com. opensymphony. xwork2.config. configurationmanager. getconfiguration (configurationmanager. java: 61) at Org. apache. struts2.dispatcher. dispatcher. getcontainer (dispatcher. java: 774) at Org. apache. struts2.dispatcher. ng. initoperations. initstaticcontentloader (initoperations. java: 77) at Org. apache. struts2.dispatcher. ng. filter. strutsprepareandexecutefilter. init (strutsprepareandexecutefilter. java: 49) at Org. apache. catalina. core. applicationfilterconfig. getfilter (applicationfilterconfig. java: 275) at Org. apache. catalina. core. applicationfilterconfig. setfilterdef (applicationfilterconfig. java: 397) at Org. apache. catalina. core. applicationfilterconfig. <init> (applicationfilterconfig. java: 108) at Org. apache. catalina. core. standardcontext. filterstart (standardcontext. java: 3800) at Org. apache. catalina. core. standardcontext. start (standardcontext. java: 4450) at Org. apache. catalina. core. containerbase. addchildinternal (containerbase. java: 791) at Org. apache. catalina. core. containerbase. addchild (containerbase. java: 771) at Org. apache. catalina. core. standardhost. addchild (standardhost. java: 526) at Org. apache. catalina. startup. hostconfig. deploydirectory (hostconfig. java: 987) at Org. apache. catalina. startup. hostconfig. deploydirectories (hostconfig. java: 909) at Org. apache. catalina. startup. hostconfig. deployapps (hostconfig. java: 495) at Org. apache. catalina. startup. hostconfig. start (hostconfig. java: 1206) at Org. apache. catalina. startup. hostconfig. lifecycleevent (hostconfig. java: 314) at Org. apache. catalina. util. lifecyclesupport. firelifecycleevent (lifecyclesupport. java: 119) at Org. apache. catalina. core. containerbase. start (containerbase. java: 1053) at Org. apache. catalina. core. standardhost. start (standardhost. java: 722) at Org. apache. catalina. core. containerbase. start (containerbase. java: 1045) at Org. apache. catalina. core. standardengine. start (standardengine. java: 443) at Org. apache. catalina. core. standardservice. start (standardservice. java: 516) at Org. apache. catalina. core. standardserver. start (standardserver. java: 710) at Org. apache. catalina. startup. catalina. start (Catalina. java: 583) at Sun. reflect. nativemethodaccessorimpl. invoke0 (native method) at Sun. reflect. nativemethodaccessorimpl. invoke (nativemethodaccessorimpl. java: 39) at Sun. reflect. delegatingmethodaccessorimpl. invoke (delegatingmethodaccessorimpl. java: 25) at java. lang. reflect. method. invoke (method. java: 597) at Org. apache. catalina. startup. bootstrap. start (Bootstrap. java: 288) at Org. apache. catalina. startup. bootstrap. main (Bootstrap. java: 413) 22:26:44 Org. apache. catalina. core. serious standardcontext start: Error filterstart

　　

After diagnosis, This is a bug in myeclipse. This is a space in the tomcat installation directory, for example, Tomcat 6.0. Rename the directory as Tomcat 6.

Why <constant name = "struts. devmode" value = "true"/> is added to struts. xml?