[slf4j-dev] [GIT] SLF4J: Simple Logging Facade for Java branch, master, updated. v1.5.9.RC1-16-gcfb117d
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- Log -----------------------------------------------------------------
http://git.qos.ch/gitweb/?p=slf4j.git;a=commit;h=cfb117d9e4c0fc44313328e8a8f9b74ad9bbf622
http://github.com/ceki/slf4j/commit/cfb117d9e4c0fc44313328e8a8f9b74ad9bbf622
commit cfb117d9e4c0fc44313328e8a8f9b74ad9bbf622
Author: Ceki Gulcu <ceki at qos.ch>
Date: Sun Dec 27 00:54:37 2009 +0100
- added "In the presence of an exception/throwable, is it possible to
parametizere a logging statement?"
- mentioning provided scope as a convenient method for excluding
commons-logging
diff --git a/slf4j-site/src/site/pages/faq.html b/slf4j-site/src/site/pages/faq.html
index 7e1223c..7da0d9d 100644
--- a/slf4j-site/src/site/pages/faq.html
+++ b/slf4j-site/src/site/pages/faq.html
@@ -130,6 +130,9 @@
without going through the static methods in
<code>LoggerFactory</code>? </a></li>
+ <li><a href="#paramException">In the presence of an
+ exception/throwable, is it possible to parametizere a logging
+ statement?</a></li>
</ol>
@@ -543,16 +546,37 @@ org.slf4j.impl.StaticLoggerBinder.SINGLETON from class org.slf4j.LoggerFactory
</dt>
<dd>
- <p>A large number of Maven projects declare commons-logging
- as a dependency. Thus, if you wish to migrate to SLF4J or use
+ <p>A large number of Maven projects declare commons-logging as a
+ dependency. Thus, if you wish to migrate to SLF4J or use
jcl-over-slf4j, you would need to declare a commons-logging
- exclusion in all of your dependencies which transitively
- depend on commons-logging. This can be an error prone
- process. To alleviate the pain, Erik van Oosten has developed
- a <a
+ exclusion in all of your dependencies which transitively depend
+ on commons-logging. This can be an error prone process. To
+ alleviate the pain, Erik van Oosten has developed a <a
href="http://day-to-day-stuff.blogspot.com/2007/10/announcement-version-99-does-not-exist.html">clever
hack around this problem.</a>
</p>
+
+ <p>Alternatively, commons-logging can be rather simply and
+ conveniently excluded as a dependency by declaring it in the
+ <em>provided</em> scope within the pom.xml file of your
+ project. The actual commons-logging classes would be provided by
+ jcl-over-slf4j. This translates into the following pom file
+ snippet:</p>
+
+ <pre class="prettyprint source"><dependency>
+ <groupId>commons-logging</groupId>
+ <artifactId>commons-logging</artifactId>
+ <version>1.1.1</version>
+ <scope>provided</scope>
+</dependency>
+
+<dependency>
+ <groupId>org.slf4j</groupId>
+ <artifactId>jcl-over-slf4j</artifactId>
+ <version>${project.version}</version>
+</dependency></pre>
+
+
</dd>
@@ -980,11 +1004,62 @@ logger.debug("The new entry is {}.", entry);</pre>
<code>ILoggerFactory</code> interface as an alternative to
inventing your own logging API.</p>
</dd>
+
+ <dt><a name="paramException" href="#paramException">In the presence of an
+ exception/throwable, is it possible to parametizere a logging
+ statement?</a></dt>
+
+
+ <dd>
+ <p>No. The SLF4J API does not support parametization in the
+ presence of an exception. Thus,
+ </p>
+ <pre class="prettyprint">String s = "Hello world";
+try {
+ throw new NumberFormatException("...");
+} catch (NumberFormatException e) {
+ logger.error("Failed to format {}", s, e);
+}</pre>
+ <p>will <b>NOT</b> print the <code>NumberFormatException</code> nor its
+ stack trace. The java compiler will invoke the <a
+ href="http://www.slf4j.org/apidocs/org/slf4j/Logger.html#error%28java.lang.String,%20java.lang.Object,%20java.lang.Object%29">error
+ method taking a String and two Object arguments</a>, which,
+ contrary to the programmer's most probable intention, will cause
+ the <code>NumberFormatException</code> to be ignored. This is one
+ of the unfortunate warts present in the SLF4J API.
+ </p>
+ <p>The only way to have the exception treated properly, is to
+ invoke the <a
+ href="http://www.slf4j.org/apidocs/org/slf4j/Logger.html#error%28java.lang.String,%20java.lang.Throwable%29">error
+ method taking a String and a Throwable</a>. The correct code is
+ then,</p>
+
+ <pre class="prettyprint">String s = "Hello world";
+try {
+ throw new NumberFormatException("...");
+} catch (NumberFormatException e) {
+ // concatenation instead of parametrization!
+ <b>logger.error("Failed to format "+ s, e);</b>
+}</pre>
- </dl>
+ <p>The second form MUST be employed in the presence of
+ exceptions. Given that exceptions are rare by definition, the cost
+ of concatenating "Failed format " and <em>s</em> should be
+ negligible in pracice.
+ </p>
+ <p>If you are user of the SLF4J API, and do not understand the
+ explanations in this question, you are advised to dwell on the
+ matter until it becomes clear. You have been warned.
+ </p>
+
+ </dd>
+
+
+
+ </dl>
-----------------------------------------------------------------------
Summary of changes:
slf4j-site/src/site/pages/faq.html | 89 +++++++++++++++++++++++++++++++++---
1 files changed, 82 insertions(+), 7 deletions(-)
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