[slf4j-dev] Release of SLF4J version 1.6.0-RC0

[Joern Huxhorn]

On 26.04.2010, at 10:58, Ceki Gülcü wrote:

> On 24/04/2010 3:55 PM, Joern Huxhorn wrote:
> 
>> One of my goals in slf4j-n was to reduce the number of methods in the
>> Logger interface.
>> This was seemingly a bad idea since it would have a performance impact,
>> in the case where a message isn't actually logged, as Ralph reported.
>> 
>> Because of this, it would be very wise to keep all the methods that are
>> already present in the Logger interface and simply add
>> debug(Message)
>> debug(Message, Throwable)
>> debug(Marker, Message)
>> debug(Marker, Message, Throwable)
>> [same for other levels plus generic log(Level, ...)-methods]
>> 
>> The designer in me doesn't like the "bloated" (in the sense that some
>> methods could be dropped without losing functionality) interface, but
>> the realist in me accepts that performance is more important than
>> aesthetics ;)
> 
> Can't we coalesce debug(Message), debug(Message, Throwable), debug(Marker, Message) and debug(Marker, Message, Throwable) into a single variant?
> 
> Here is an idea:
> 
> try {
>  ...
> } catch(Throwable t) {
> Message m = new Message("hello{}").addParam("word").add(marker).add(t);
> logger.error(m);
> }
> 
> This approach incurs the cost of creating and building the Message object regardless of whether the request will be logged or not. I suspect that the bulk of the cost is due to the object creation incurred by new Message(...) and not due to the addition of extra data incurred in calling addParam() and the other add() methods. Thus, performance-wise we are in the same position as the original Message proposal but now we can get rid of all the overloaded variants dealing with Marker and throwable.
> 

Well, the idea of the Message interface (!) was to enable lazy initialization (in contrast to a simply toString) without adding too many additional requirements to it.

http://github.com/huxi/slf4j/blob/slf4j-redesign/slf4j-n-api/src/main/java/org/slf4j/core/Message.java

It would be much more work to implement a custom Message with the suggestion above. More work implies more chances of faulty implementation, for example in case of Marker support. The addParam() method would be quite a mistake, too, since a different implementation of Message might use key/value-pairs as parameters. (This is something that I'd really like to do since it would also enable easier translations)

I see that interface as the main extension point of SLF4J & Logback. The Message instance is supposed to end up in the appenders in case of Logback, so custom appenders could handle custom Message implementations in arbitrary ways without having to parse anything.

We could, however, add the Throwable to the Message interface. I left it out of the interface and added it only to the ParameterizedMessage implementation to keep the interface as clean as possible.

This would reduce the interface to debug(Message) and debug(Marker, Message), at least.

How about 

interface Message
{
	Message set(Throwable); // instead of setThrowable to be more concise?
	Throwable getThrowable();
}

in addition?

My problem is: I'm not really sure if I'll like this while using it ;)
Regardless of the way we'll implement it in the Message, it will always be less concise (concerning both brevity and readability) than code using the four methods...

Joern.