You can only use at most 2 placeholders like that. If you need 3 or more, you have to do it the old fashion way.
Unfortunately sfl4j doesn't support varargs.

slfj4 also has the following interface:

public void info(String format, Object[] argArray);

With this it's possible to get rid of the isXXXEnabled() statements.

I also found some log statements like this one:

if (log.isInfoEnabled()) {
    log.info("Loaded " + typeMappings.size() + " type converters in " + TimeUtils.printDuration(watch.stop()));
}

which we could refactor to

log.info("Loaded {} type converters in {}"), typeMappings.size(), TimeUtils.printDuration(watch.stop());

but I assume "TimeUtils.printDuration(watch.stop())" is an expensive operation which should only be executed if we want log this statement. Therefore I would refactor some similar parts of the code to

if (log.isInfoEnabled()) {
    log.info("Loaded {} type converters in {}"), typeMappings.size(), TimeUtils.printDuration(watch.stop());
}

Committed r1084858
removed the unnecessary isInfoEnabled() statements

Committed r1085587
removed the unnecessary isTraceEnabled() statements in camel-core

Committed r1086028
removed the unnecessary isTraceEnabled() statements in components

Committed r1089960
removed the unnecessary isDebugEnabled() statements in camel-core

Christian you cannot just do this everywhere. The single line is only possible if the parameters is not to be computed or creating new objects.

So the ones who creates a new Object[] for the parameters etc, should still be guarded with the isDebugEnabled etc.
Also some of the operations on the parameters may take time to compute, so its really not always a good idea.

IMHO the isXXX should be used when the parameters are not simple and if they invoke operations to get data (and the operation is not a simple getter, the compiler can inline).

That's exactly what I want/did. I will review my changes. May be I was to optimistic by some getters or ...

Christian is there any more work on this?

Unfortunately yes. At present I work on to remove the unnecessary isDebugEnabled() in the camel components. Afterwards I have to review my first commits as you suggested. I think I can finish this work until end of next week (5/29/2011).

Committed r1134194
removed the unnecessary isDebugEnabled() statements in components
Have to go through my previous commits and check they

Christian can you look into this, as we would like to be ready to cut Camel 2.8 later this month.