WebLogic information extraction

Yikes, I see your confusion -- I left out the extraction of the server details needed to build the array. Sorry about that. I think this is more what you are after:

when HTTP_RESPONSE {
  if { [HTTP::header exists "X-WebLogic-Cluster-List"] }{
    set server_mappings [split [HTTP::header "X-WebLogic-Cluster-List"] "|" ]
    init array if non-existent
    array set ::ServerList { }
    clear pre-existing array entries
    (re-initializing as blank array doesn't seem to do it)
    array unset ::ServerList
    foreach servermap $server_mappings {
      set serverID [getfield $servermap "!" 1]
      set serverName [getfield $servermap "!" 2]
      set ::ServerList($serverID) [getfield [findclass $serverName $::server_name_to_IP] " " 2]
    }
  }
}

or to eliminate setting those 2 extra variables, inline substitution gives you:

when HTTP_RESPONSE {
  if { [HTTP::header exists "X-WebLogic-Cluster-List"] }{
    set server_mappings [split [HTTP::header "X-WebLogic-Cluster-List"] "|" ]
    init array if non-existent
    array set ::ServerList { }
    clear pre-existing array entries
    (re-initializing as blank array doesn't seem to do it)
    array unset ::ServerList
    foreach servermap $server_mappings {
      set ::ServerList([getfield $servermap "!" 1]) [getfield [findclass [getfield $servermap "!" 2] $::server_name_to_IP] " " 2]
    }
  }
}

Clear as mud, now, eh?

(getfield starts indexing @ 1, while lindex starts @ 0.)