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https://issues.apache.org/jira/browse/LUCENE-1482?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12848571#action_12848571
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Shai Erera commented on LUCENE-1482:
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Well ... since Mark hasn't closed it yet (thanks Mark :)), I thought to try
once more. Perhaps w/ the merge of Lucene/Solr this will look more reasonable
now? I personally feel that just setting InfoStream on IW is not enough. I
don't think we need to control logging per level either. I think it's important
to introduce this in at least one of the following modes:
# We add SLF4J and allow the application to control logging per package(s), but
the logging level won't matter - as long as it's not OFF, we log.
# We add a static factory LuceneLogger or something, which turns logging
on/off, in which case all components/packages either log or not.
I think (1) gives us greater flexibility (us as in the apps developers), but
(2) is also acceptable. As long as we can introduce logging messages from more
components w/o passing infoStream around ... On LUCENE-2339 for example, a
closeSafely method was added which suppresses IOExceptions that may be caused
by io.close(). You cannot print the stacktrace because that would be
unacceptable w/ products that are not allowed to print anything unless logging
has been enabled, but on the other hand suppressing the exception is not good
either ... in this case, a LuceneLogger could have helped because you could
print the stacktrace if logging was enabled.
> Replace infoSteram by a logging framework (SLF4J)
> -------------------------------------------------
>
> Key: LUCENE-1482
> URL: https://issues.apache.org/jira/browse/LUCENE-1482
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Index
> Reporter: Shai Erera
> Fix For: 3.1
>
> 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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