Grokbase Groups Lucene dev May 2010
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Shai Erera closed LUCENE-1482.

Resolution: Won't Fix

Closing this one as we clearly don't reach a consensus about it. And it introduces a static variable to each class that is interested in logging, which is a problem if Lucene is used inside the same JVM by several instances - turning the logging on for one application will affect all the rest as well.

Anyway, it's been open for too long and I don't see that we're anywhere near a consensus (perhaps rightfully), so no point keeping it open.
Replace infoSteram by a logging framework (SLF4J)

Key: LUCENE-1482
Project: Lucene - Java
Issue Type: Improvement
Components: Index
Reporter: Shai Erera
Fix For: 4.0

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()) {
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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postedMay 31, '10 at 6:18p
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