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From "Shai Erera (JIRA)" <>
Subject [jira] Commented: (LUCENE-1482) Replace infoSteram by a logging framework (SLF4J)
Date Thu, 11 Jun 2009 07:23:07 GMT


Shai Erera commented on LUCENE-1482:

I'm not even sure if this issue should be kept around, given the responses I got to it. The
question is - do we think logging should be improved in Lucene or not? If YES, then let's
keep the issue around and come back in 3.0. If NO, then let's cancel it. It hasn't been commented
on for ~6 months, so there's no point to keep it around unless we think it should be resolved
at some point

> Replace infoSteram by a logging framework (SLF4J)
> -------------------------------------------------
>                 Key: LUCENE-1482
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Index
>            Reporter: Shai Erera
>             Fix For: 3.0
>         Attachments: LUCENE-1482-2.patch, LUCENE-1482.patch, slf4j-api-1.5.6.jar, slf4j-nop-1.5.6.jar
> Lucene makes use of infoStream to output messages in its indexing code only. For debugging
purposes, when the search application is run on the customer side, getting messages from other
code flows, like search, query parsing, analysis etc can be extremely useful.
> There are two main problems with infoStream today:
> 1. It is owned by IndexWriter, so if I want to add logging capabilities to other classes
I need to either expose an API or propagate infoStream to all classes (see for example DocumentsWriter,
which receives its infoStream instance from IndexWriter).
> 2. I can either turn debugging on or off, for the entire code.
> Introducing a logging framework can allow each class to control its logging independently,
and more importantly, allows the application to turn on logging for only specific areas in
the code (i.e., org.apache.lucene.index.*).
> I've investigated SLF4J (stands for Simple Logging Facade for Java) which is, as it names
states, a facade over different logging frameworks. As such, you can include the slf4j.jar
in your application, and it recognizes at deploy time what is the actual logging framework
you'd like to use. SLF4J comes with several adapters for Java logging, Log4j and others. If
you know your application uses Java logging, simply drop slf4j.jar and slf4j-jdk14.jar in
your classpath, and your logging statements will use Java logging underneath the covers.
> This makes the logging code very simple. For a class A the logger will be instantiated
like this:
> public class A {
>   private static final logger = LoggerFactory.getLogger(A.class);
> }
> And will later be used like this:
> public class A {
>   private static final logger = LoggerFactory.getLogger(A.class);
>   public void foo() {
>     if (logger.isDebugEnabled()) {
>       logger.debug("message");
>     }
>   }
> }
> That's all !
> Checking for isDebugEnabled is very quick, at least using the JDK14 adapter (but I assume
it's fast also over other logging frameworks).
> The important thing is, every class controls its own logger. Not all classes have to
output logging messages, and we can improve Lucene's logging gradually, w/o changing the API,
by adding more logging messages to interesting classes.
> I will submit a patch shortly

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