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From "Uwe Schindler (Created) (JIRA)" <>
Subject [jira] [Created] (LUCENE-3598) Improve InfoStream class in trunk to be more consistent with logging-frameworks like slf4j/log4j/commons-logging
Date Sat, 26 Nov 2011 10:09:41 GMT
Improve InfoStream class in trunk to be more consistent with logging-frameworks like slf4j/log4j/commons-logging

                 Key: LUCENE-3598
             Project: Lucene - Java
          Issue Type: Improvement
          Components: core/index
    Affects Versions: 4.0
            Reporter: Uwe Schindler

Followup on a [thread by Shai Erea on java-dev@lao|]:
I already discussed with Robert about that, that there is one thing missing. Currently the
IW only checks if the infoStream!=null and then passes the message to the method, and that
*may* ignore it. For your requirement it is the case that this is enabled or disabled dynamically.
Unfortunately if the construction of the message is heavy, then this wastes resources.

I would like to add another method to this class: abstract boolean isMessageEnabled() that
can also be implemented. I would then replace all null checks in IW by this method. The default
config in IW would be changed to use a NoOutputInfoStream that returns false here and ignores
the message.

A simple logger wrapper for e.g. log4j / slf4j then could look like (ignoring component, could
be enabled):

Loger log = YourLoggingFramework.getLogger(IndexWriter.class);

public void message(String component, String message) {
  log.debug(component + ": " + message);

public boolean isMessageEnabled(String component) {
  return log.isDebugEnabled();

Using this you could enable/disable logging live by e.g. the log4j management console of your
app server by enabling/disabling IndexWriter.class logging.

The changes are really simple:
- PrintStreamInfoStream returns true, always, mabye make it dynamically enable/disable to
allow Shai's request
- infoStream.getDefault() is never null and can never be set to null. Instead the default
is a singleton NoOutputInfoStream that returns false of isMessageEnabled().
- All null checks on infoStream should be replaced by infoStream.isMessageEanbled(component),
this is possible as always != null. There are no slowdowns by this - it's like Collections.emptyList()
instead stupid null checks.

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