To migrate to Struts 2.1 :

1. Follow instructions
http://cwiki.apache.org/S2WIKI/troubleshooting-guide-migrating-from-struts-20x-to-21x.html
just ignore change related to web.xml StrutsPrepareAndExecuteFilter usage - it will not work with Sitemesh as it will strap all attributes

2. Update web.xml with appropriate filters

2.a struts-cleanup filter is not required anymore and 2 struts filter instead of one before
BEFORE 2.1 :
    <filter>
        <filter-name>struts-cleanup</filter-name>
        <filter-class>org.apache.struts2.dispatcher.ActionContextCleanUp</filter-class>
    </filter>
    <filter>
        <filter-name>struts</filter-name>
        <filter-class>org.apache.struts2.dispatcher.FilterDispatcher</filter-class>
    </filter>
AFTER :
    <filter>
      <filter-name>struts2-prepare</filter-name>
      <filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareFilter</filter-class>
      <init-param>
        <param-name>actionPackages</param-name>
        <param-value>com.peak6.weseed.webapp.admin.action</param-value>
      </init-param>
    </filter>
    <filter>
      <filter-name>struts2-execute</filter-name>
      <filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsExecuteFilter</filter-class>
      <init-param>
        <param-name>actionPackages</param-name>
        <param-value>com.peak6.weseed.webapp.admin.action</param-value>
      </init-param>
    </filter>
2.b sitemesh filter should sit in the middle of two struts filters:
BEFORE 2.1 :
    <filter-mapping>
        <filter-name>struts-cleanup</filter-name>
        <url-pattern>/*</url-pattern>
        <dispatcher>REQUEST</dispatcher>
        <dispatcher>FORWARD</dispatcher>
    </filter-mapping>
    <filter-mapping>
        <filter-name>sitemesh</filter-name>
        <url-pattern>/*</url-pattern>
        <dispatcher>REQUEST</dispatcher>
        <dispatcher>FORWARD</dispatcher>
        <dispatcher>INCLUDE</dispatcher>
    </filter-mapping>
    <filter-mapping>
        <filter-name>struts</filter-name>
        <url-pattern>/*</url-pattern>
        <dispatcher>REQUEST</dispatcher>
        <dispatcher>FORWARD</dispatcher>
    </filter-mapping>
AFTER :
    <filter-mapping>
        <filter-name>struts2-prepare</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>
    <filter-mapping>
        <filter-name>sitemesh</filter-name>
        <url-pattern>/*</url-pattern>
        <dispatcher>FORWARD</dispatcher>
        <dispatcher>REQUEST</dispatcher>
        <dispatcher>INCLUDE</dispatcher>
    </filter-mapping>
    <filter-mapping>
        <filter-name>struts2-execute</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

3. You may remove Codebehind Plugin (optional) as since 2.1 this plugin has been deprecated in favor of the Convention Plugin

Patch for doing the upgrade. I tried, but it fails b/c users have to login for each page request. Also, signup fails with the following error:

Signup:
WARN [btpool0-3] VisitorFieldValidator.warn(45) | The visited object is null, VisitorValidator will not be able to handle validation properly. Please make sure the visited object is not null for VisitorValidator to function properly
WARN [btpool0-3] Dispatcher.warn(49) | Could not find action or result
No result defined for action org.appfuse.webapp.action.SignupAction and result input

I posted the following question on the Struts mailing list - no solution yet.

http://www.mail-archive.com/user@struts.apache.org/msg87713.html

Integration tests now pass on web/struts. However, integration tests still test when creating an archetype. Not sure why.

     [exec] PasswordHint:
     [exec] DEBUG [btpool0-3] PasswordHintAction.execute(45) | Processing Password Hint...
     [exec] WARN [btpool0-3] Dispatcher.warn(49) | Could not find action or result
     [exec] No result defined for action com.mycompany.webapp.action.PasswordHintAction and result success
     [exec] at com.opensymphony.xwork2.DefaultActionInvocation.executeResult(DefaultActionInvocation.java:363)

Archetypes now work thanks to Dustin Pearce's help. Still need to refactor to use the convention plugin and change AMP to generate convention-friendly code.

Did you manage to solve the issue you mentioned on April 25th?:

"I tried, but it fails b/c users have to login for each page request."

I'm currently facing the same problem and would love to know what causes it.

If you look at the FishEye tab on this issue, you should see all the changes related to it. Hopefully that'll help:

http://issues.appfuse.org/browse/APF-1130?page=com.atlassian.jira.ext.fisheye:fisheye-issuepanel

Thanks, I wasn't sure whether it was solved, but I understand it was. Now I also understand the response on the Struts mailing list: I missed the switch from struts2-codebehind-plugin to struts2-convention-plugin in the pom.

Hi Matt,
I vote for it because JSON plugin bundled with Strus 2.1.7+ and by JSON plugin I'll use jQuery.
BTW it's possible to plug JSON plugin to earlier version.
Good luck.