关于Struts2中的struts.devMode

devMode模式是开发模式，开启它则默认开启了i18n.reload、configuration.xml.reload。
### when set to true, Struts will act much more friendly for developers. This
### includes:
### - struts.i18n.reload = true
### - struts.configuration.xml.reload = true
### - raising various debug or ignorable problems to errors
###   For example: normally a request to foo.action?someUnknownField=true should
###                be ignored (given that any value can come from the web and it
###                should not be trusted). However, during development, it may be
###                useful to know when these errors are happening and be told of
###                them right away.
下面是4个开发模式常用配置的简介---

开启使用开发模式，详细错误提示

<constant name="struts.devMode" value="true"/>

指定每次请求到达，重新加载资源文件

<constant name="struts.i18n.reload" value="true"/>

指定每次配置文件更改后，自动重新加载

<constant name="struts.configuration.xml.reload" value="true"/>

指定XSLT Result使用样式表缓存

<constant name="struts.xslt.nocache" value="true"/>

网上有一篇文章比较好，现在借鉴一下
当配置好如下信息的时候

<constant name="struts.devMode" value="true"/> 或者
<constant name="struts.configuration.xml.reload" value="true"/>

有时启动tomcat报错
org.apache.catalina.core.StandardContext filterStart
严重: 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.FilterDispatcher.init(FilterDispatcher.java:191)
    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:3709)
    at org.apache.catalina.core.StandardContext.start(StandardContext.java:4363)
    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:525)
    at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:926)
    at org.apache.catalina.startup.HostConfig.deployDirectories(HostConfig.java:889)
    at org.apache.catalina.startup.HostConfig.deployApps(HostConfig.java:492)
    at org.apache.catalina.startup.HostConfig.start(HostConfig.java:1149)
    at org.apache.catalina.startup.HostConfig.lifecycleEvent(HostConfig.java:311)
    at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:117)
    at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1053)
    at org.apache.catalina.core.StandardHost.start(StandardHost.java:719)
    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:578)
    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)
2009-2-4 22:40:54 org.apache.catalina.core.StandardContext start
严重: Error filterStart
2009-2-4 22:40:54 org.apache.catalina.core.StandardContext start
严重: Context [/Struts2Demo2] startup failed due to previous errors

可以先检查一下tomcat的安装路径是否包含空格