I'm not sur it is the best way to do it,  but to ackieve it in AS7.0.2 , actually I've added a directory in  standalone/deployements/mydirectory.war  with an   web.xml in a WEB--INF subdirectory with expiredfilter to define cache-expired.

{code:xml}<?xml version="1.0"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
      version="3.0"> 
 <description>My static resources</description>
 <display-name>My static resources</display-name>
<filter>
 <filter-name>ExpiresFilter</filter-name>
 <filter-class>org.apache.catalina.filters.ExpiresFilter</filter-class> 
 <init-param>
    <param-name>ExpiresByType image</param-name>
    <param-value>access plus 1 month</param-value>
 </init-param>
</filter>
 
 
<filter-mapping>
 <filter-name>ExpiresFilter</filter-name>
 <url-pattern>/*</url-pattern>
 <dispatcher>REQUEST</dispatcher>
</filter-mapping>
</web-app>
{code}

To deploy it you 'll have to add a file of the war name suffixed by '.dodeploy'  at standalone/deployements/mydirectory.war.dodeploy

The you can access to resources like this http://localhost:8080/mydirectory/..../x.png

If you need to dynamically write in this dir from another .war/.ear then you can write in using

String pathSeparator = System.getProperty("file.separator");

String path =System.getProperties().get("jboss.server.base.dir") +pathSeparator+"deployments"+pathSeparator+"mydirectory.war"+pathSeparator+"photos"+pathSeparator;

If I clean standalone/data or your standaline.xml I need to recreate file mydirectory.war.dodeploy to redeploy it

If there is a best solution I'm also interessed to know how to do this.

May be an expert can tell us if it is the best way to store static resources?

Bests regards