How to get value from a map stored on a httpsession when running on Tomcat

Question

With Tomcat, it is possible to dump a pile of interesting information to the a logfile by configuring the appropriate valve.

For example:

       <Valve className="org.apache.catalina.valves.AccessLogValve" 
        directory="logs"  
        prefix="localhost." 
        suffix=".txt" 
        pattern='%s %b %I %{myname}s' 
        resolveHosts="false"/>

means:

• %s - output HTTP status code of the response
• %b - output Bytes sent,excluding HTTP headers, or '-' if zero
• %I - threadId

and %{myname}s meaning output the value of the attribute myname stored on the session.

All good. If I have a hashmap stored on my session, I can output by doing something like:

%{mymap}s

See http://tomcat.apache.org/tomcat-5.5-doc/config/valve.html for more info.

But, I want to just output a value for a specific key, not the entire map. I have tried:

%{mymap.myatt}s

But this does not work. Any ideas how to do this?

Answer 1

Looking in the source for AccessLogValve, search for the String SessionAttributeElement. This is what the value is doing to translate your %{mymap}s to a string, and it does not look like you can drill down into the map.

You could extend this class and override the createAccessLogElement method to add in another handler for a different pattern (lets say %{mymap.myatt}m), and then handle the logic in a similar fashion to the SessionAttributeElement class, but split the header into the session attribute name and map key.