Missing message for key "index.title"

Missing message for key "index.title"

问题是找不ApplicationResources.properties
或者：Cannot find message resources under key org.apache.struts.action.MESSAGE
问题是找不ApplicationResources.properties
这个要在文件：struts-config 中设置
如：ApplicationResources.properties放在classes/book的文件下，就可以设如下：
</action-mappings>
<message-resources parameter="book/ApplicationResources"/>
</struts-config>

在web.xml中
<init-param>
<param-name>application</param-name>
<param-value>ApplicationResources</param-value>
</init-param>