[logback-user] Joran and variable substitution

[Ralph Goers]

If all you are looking for is variable replacement then you could look at commons-lang's StrSubstitutor class.  Commons Configuration's ConfigurationInterpolator provides an example of how it can be used to resolve variables from multiple StrLookup sources, including SLF4J's MDCLookup. 

Ralph

On Dec 30, 2010, at 1:18 PM, Oliver Geishuettner wrote:

> 
> Thanks for the hint, this lead me in the right direction !
> I found out that a simple context.subst in e.g. the begin part of the action is sufficient. To make things easier for me I created a small helper class: 
> 
> public final class VariableHelper {
> final static Logger log = LoggerFactory.getLogger(VariableHelper.class);
> 
> private InterpretationContext context = null;
> private Attributes attrs = null;
> 
> private VariableHelper( InterpretationContext context, Attributes attrs ) {
>  this.context = context;
>  this.attrs = attrs;  
> }
> 
> public static String replace(final InterpretationContext ic,
>   final String str) {
>  String ret = null;
>  log.debug("before subst '{}'", str);
>  ret = ic.subst(str);
>  log.debug("after subst: '{}'", ret);
> 
>  return ret;
> }
> 
> public static String replace(final InterpretationContext ic,
>   final Attributes attrs, final String attrName) {
>  return replace(ic, attrs.getValue(attrName));
> }
> 
> public String replace( String attrName ) {
>  return replace( context, attrs, attrName );
> }
> 
> public static VariableHelper createInstance( final InterpretationContext context, final Attributes attrs ) {
>  return new VariableHelper( context, attrs );
> }
> }
> 
> This class can be used like this:
> 
> public class FooBarAction extends Action {
> public void begin(InterpretationContext context, String arg1,
>   Attributes attributes) throws ActionException {
>  VariableHelper vh = VariableHelper.createInstance(context, attributes);
> 
>  String foo = vh.replace("foo");
>  String bar = vh.replace("sbar");
> ...
> 
> This is a replacement for:
> 
> String foo = attributes.getValue( "foo" );
> foo = context.subst("foo" );
> 
> Perhaps this is of help for somebody.
> -------- Original-Nachricht --------
>> Datum: Thu, 30 Dec 2010 13:35:37 +0100
>> Von: Ceki Gulcu <ceki at qos.ch>
>> An: logback users list <logback-user at qos.ch>
>> Betreff: Re: [logback-user] Joran and variable substitution
> 
>> Hi Marge,
>> 
>> Variable substitution is done by Joran actions on an individual
>> basis. Search for usages of the subst() method of the
>> InterpretationContext class.
> 
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