Replace infoSteram by a logging framework (SLF4J)
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Key: LUCENE-1482
URL: https://issues.apache.org/jira/browse/LUCENE-1482
Project: Lucene - Java
Issue Type: Improvement
Components: Index
Reporter: Shai Erera
Priority: Minor
Fix For: 2.4.1, 2.9
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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