Modified: websites/production/logging/content/log4cxx/0.10.0/usage.html
==============================================================================
--- websites/production/logging/content/log4cxx/0.10.0/usage.html (original)
+++ websites/production/logging/content/log4cxx/0.10.0/usage.html Thu Nov 22
09:01:01 2018
@@ -15,11 +15,11 @@
See the License for the specific language governing permissions and
limitations under the License.
-->
-<!-- Generated by Apache Maven Doxia at 2018-01-27 -->
+<!-- Generated by Apache Maven Doxia at 2018-11-22 -->
<html xmlns="http://www.w3.org/1999/xhtml"; xml:lang="en" lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html;
charset=UTF-8" />
- <title>log4cxx -
+ <title>log4cxx -
How to use Apache log4cxx - Apache log4cxx</title>
<link rel="stylesheet" href="./css/bootstrap.min.css"
type="text/css" />
<link rel="stylesheet" href="./css/site.css" type="text/css" />
@@ -27,9 +27,9 @@
<script type="text/javascript"
src="./js/bootstrap.min.js"></script>
<script type="text/javascript"
src="./js/prettify.min.js"></script>
<script type="text/javascript" src="./js/site.js"></script>
- <meta name="Date-Revision-yyyymmdd" content="20180127" />
+ <meta name="Date-Revision-yyyymmdd" content="20181122" />
<meta http-equiv="Content-Language" content="en" />
-
+
</head>
<body class="composite">
<a href="https://logging.apache.org/";>
@@ -44,31 +44,31 @@
<a class="brand"
href="http://logging.apache.org/log4cxx";>Apache log4cxx ™</a>
<ul class="nav">
<li>
-
-
+
+
<a href="https://wiki.apache.org/logging";
class="external" target="_blank" title="Logging Wiki">Logging Wiki</a>
</li>
<li>
-
-
+
+
<a href="https://www.apache.org/";
class="external" target="_blank" title="Apache">Apache</a>
</li>
<li>
-
-
+
+
<a href="https://logging.apache.org/";
class="external" target="_blank" title="Logging Services">Logging Services</a>
</li>
<li>
-
-
+
+
<a
href="https://github.com/apache/logging-log4cxx"; class="external"
target="_blank" title="GitHub">GitHub</a>
</li>
</ul>
<div class="pull-right">
-
-
- <span id="publishDate">Last
Published: 2018-01-27</span>
+
+
+ <span id="publishDate">Last
Published: 2018-11-22</span>
<span
class="divider">|</span> <span id="projectVersion">Version: 0.10.0</span>
</div>
</div>
@@ -125,8 +125,8 @@
<a
href="issue-tracking.html" title="Issue Tracking">Issue Tracking</a>
</li>
<li class="none">
-
-
+
+
<a
href="http://wiki.apache.org/logging-log4cxx"; class="external" target="_blank"
title="Wiki">Wiki</a>
</li>
</ul>
@@ -162,23 +162,23 @@
<ul class="nav nav-list">
<li class="nav-header"><i
class="icon-info-sign"></i>Apache</li>
<li class="none">
-
-
+
+
<a href="http://www.apache.org";
class="external" target="_blank" title="Home">Home</a>
</li>
<li class="none">
-
-
+
+
<a
href="http://www.apache.org/foundation/sponsorship.html"; class="external"
target="_blank" title="Sponsorship">Sponsorship</a>
</li>
<li class="none">
-
-
+
+
<a
href="http://www.apache.org/foundation/thanks.html"; class="external"
target="_blank" title="Thanks">Thanks</a>
</li>
<li class="none">
-
-
+
+
<a href="http://www.apachecon.com";
class="external" target="_blank" title="Conferences">Conferences</a>
</li>
</ul>
@@ -204,10 +204,10 @@
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License. -->
-
+
<div class="section">
<h2>Loggers<a name="Loggers"></a></h2>
-
+
<p>
Log4cxx has three main components:
<i>loggers</i>,
<i>appenders</i> and <i>layouts</i>. These
three types of
@@ -216,10 +216,10 @@
messages are formatted and where they are
reported.
</p>
-
+
<div class="section">
<h3>Hierarchy<a name="Hierarchy"></a></h3>
-
+
<p>
The first and foremost advantage of any
logging API over plain
<tt>std::cout</tt> resides in its
ability to disable
@@ -229,17 +229,17 @@
developer-chosen criteria.
</p>
-
+
<p>
Loggers are named entities. Logger
names are case-sensitive and
they follow the hierarchical naming
rule:
</p>
-
+
<dl>
-
+
<dt><b>Named Hierarchy</b></dt>
-
+
<dd>
A logger is said to be an
<i>ancestor</i> of another
logger if its name followed by
a dot is a prefix of the
@@ -249,7 +249,7 @@
</dd>
</dl>
-
+
<p>
For example, the logger named
<tt>"com.foo"</tt> is a parent
of the logger named
<tt>"com.foo.Bar"</tt>. Similarly,
@@ -258,21 +258,21 @@
should be familiar to most developers.
</p>
-
+
<p>
The root logger resides at the top of
the logger hierarchy. It
is exceptional in two ways:
</p>
-
+
<ol style="list-style-type: decimal">
-
+
<li> it always exists,</li>
-
+
<li> it cannot be retrieved by name.</li>
</ol>
-
+
<p>
Invoking the class static <a
href="apidocs/classlog4cxx_1_1_logger.html#afc0e4d99cab7c38a2851d41e6edc1dee">log4cxx::Logger::getRootLogger</a>
method retrieves it. All other loggers
are instantiated and retrieved with the class static
@@ -281,7 +281,7 @@
class are listed below.
</p>
-
+
<div>
<pre class="prettyprint linenums">
namespace log4cxx {
@@ -308,10 +308,10 @@ namespace log4cxx {
#define LOG4CXX_FATAL(logger, expression) ...</pre></div>
</div>
-
+
<div class="section">
<h3>Levels<a name="Levels"></a></h3>
-
+
<p>
Loggers <i>may</i> be assigned levels.
The pre-defined
levels: TRACE, DEBUG, INFO, WARN, ERROR
and FATAL are defined in the
@@ -319,19 +319,19 @@ namespace log4cxx {
class which provides accessor functions.
</p>
-
+
<p>
If a given logger is not assigned a
level, then it inherits
one from its closest ancestor with an
assigned level. More
formally:
</p>
-
+
<dl>
-
+
<dt><b>Level Inheritance</b></dt>
-
+
<dd>
The <i>inherited level</i> for
a given logger <i>C</i>, is equal to the
first non-null level in the
logger hierarchy, starting at <i>C</i> and
@@ -339,69 +339,69 @@ namespace log4cxx {
</dd>
</dl>
-
+
<p>
To ensure that all loggers can
eventually inherit a level,
the root logger always has an assigned
level.
</p>
-
+
<p>
Below are four tables with various
assigned level values and the
resulting inherited levels according to
the above rule.
</p>
-
+
<table class="bodyTable" border="1"><caption align="bottom">Example 1</caption>
-
+
<tr class="a">
-
+
<th>Logger name</th>
-
+
<th>Assigned level</th>
-
+
<th>Inherited level</th>
</tr>
-
+
<tr class="b" align="left">
-
+
<td>root</td>
-
+
<td>Proot</td>
-
+
<td>Proot</td>
</tr>
-
+
<tr class="a" align="left">
-
+
<td>X </td>
-
+
<td>none</td>
-
+
<td>Proot</td>
</tr>
-
+
<tr class="b" align="left">
-
+
<td>X.Y </td>
-
+
<td>none</td>
-
+
<td>Proot</td>
</tr>
-
+
<tr class="a" align="left">
-
+
<td>X.Y.Z</td>
-
+
<td>none</td>
-
+
<td>Proot</td>
</tr>
-
+
</table>
-
+
<p>
In example 1 above, only the root
logger is assigned a
level. This level value,
<tt>Proot</tt>, is inherited by the
@@ -409,113 +409,113 @@ namespace log4cxx {
<tt>X.Y.Z</tt>.
</p>
-
+
<table class="bodyTable" border="1"><caption align="bottom">Example 2</caption>
-
+
<tr class="a">
-
+
<th>Logger name</th>
-
+
<th>Assigned level</th>
-
+
<th>Inherited level</th>
</tr>
-
+
<tr class="b" align="left">
-
+
<td>root</td>
-
+
<td>Proot</td>
-
+
<td>Proot</td>
</tr>
-
+
<tr class="a" align="left">
-
+
<td>X </td>
-
+
<td>Px</td>
-
+
<td>Px</td>
</tr>
-
+
<tr class="b" align="left">
-
+
<td>X.Y </td>
-
+
<td>Pxy</td>
-
+
<td>Pxy</td>
</tr>
-
+
<tr class="a" align="left">
-
+
<td>X.Y.Z</td>
-
+
<td>Pxyz</td>
-
+
<td>Pxyz</td>
</tr>
-
+
</table>
-
+
<p>
In example 2, all loggers have an
assigned level value. There
is no need for level inheritence.
</p>
-
+
<table class="bodyTable" border="1"><caption align="bottom">Example 3</caption>
-
+
<tr class="a">
-
+
<th>Logger name</th>
-
+
<th>Assigned level</th>
-
+
<th>Inherited level</th>
</tr>
-
+
<tr class="b" align="left">
-
+
<td>root</td>
-
+
<td>Proot</td>
-
+
<td>Proot</td>
</tr>
-
+
<tr class="a" align="left">
-
+
<td>X </td>
-
+
<td>Px</td>
-
+
<td>Px</td>
</tr>
-
+
<tr class="b" align="left">
-
+
<td>X.Y </td>
-
+
<td>none</td>
-
+
<td>Px</td>
</tr>
-
+
<tr class="a" align="left">
-
+
<td>X.Y.Z</td>
-
+
<td>Pxyz</td>
-
+
<td>Pxyz</td>
</tr>
-
+
</table>
-
+
<p>
In example 3, the loggers
<tt>root</tt>, <tt>X</tt> and
<tt>X.Y.Z</tt> are assigned the levels
<tt>Proot</tt>,
@@ -524,57 +524,57 @@ namespace log4cxx {
<tt>X</tt>.
</p>
-
+
<table class="bodyTable" border="1"><caption align="bottom">Example 4</caption>
-
+
<tr class="a">
-
+
<th>Logger name</th>
-
+
<th>Assigned level</th>
-
+
<th>Inherited level</th>
</tr>
-
+
<tr class="b" align="left">
-
+
<td>root</td>
-
+
<td>Proot</td>
-
+
<td>Proot</td>
</tr>
-
+
<tr class="a" align="left">
-
+
<td>X </td>
-
+
<td>Px</td>
-
+
<td>Px</td>
</tr>
-
+
<tr class="b" align="left">
-
+
<td>X.Y </td>
-
+
<td>none</td>
-
+
<td>Px</td>
</tr>
-
+
<tr class="a" align="left">
-
+
<td>X.Y.Z</td>
-
+
<td>none</td>
-
+
<td>Px</td>
</tr>
-
+
</table>
-
+
<p>
In example 4, the loggers <tt>root</tt>
and <tt>X</tt>
and are assigned the levels
<tt>Proot</tt> and <tt>Px</tt>
@@ -584,10 +584,10 @@ namespace log4cxx {
</p>
</div>
-
+
<div class="section">
<h3>Requests<a name="Requests"></a></h3>
-
+
<p>
Logging requests are made by invoking a
method of
a logger instance, preferrably through
the use of LOG4CXX_INFO or similar
@@ -595,7 +595,7 @@ namespace log4cxx {
and use of the insertion operator
(<<) in the message parameter.
</p>
-
+
<div>
<pre class="prettyprint linenums">
log4cxx::LoggerPtr
logger(log4cxx::Logger::getLogger(<b>"com.foo"</b>));
@@ -609,7 +609,7 @@ LOG4CXX_DEBUG(logger, "e^10 = "
//
LOG4CXX_WARN(logger, L"" << i << L" is the number
of the iteration.")</pre></div>
-
+
<p>
A logging request is said to be
<i>enabled</i> if its level is
higher than or equal to the level of
its logger. Otherwise, the
@@ -618,12 +618,12 @@ LOG4CXX_WARN(logger, L"" <&
summarized below.
</p>
-
+
<dl>
-
+
<dt><b>Basic Selection Rule</b></dt>
-
+
<dd>
A log request of level <i>p</i>
in a logger with (either assigned or
inherited, whichever is
appropriate) level <i>q</i>, is enabled if
@@ -631,19 +631,19 @@ LOG4CXX_WARN(logger, L"" <&
</dd>
</dl>
-
+
<p>
This rule is at the heart of log4cxx.
It assumes that levels are
ordered. For the standard levels, we
have <tt>TRACE < DEBUG < INFO
< WARN < ERROR < FATAL</tt>.
</p>
-
+
<p>
Here is an example of this rule.
</p>
-
+
<div>
<pre class="prettyprint linenums">
// get a logger instance named "com.foo"
@@ -671,28 +671,28 @@ LOG4CXX_INFO(barlogger. "Located ne
// This request is disabled, because <b>DEBUG</b> < <b>INFO</b>.
LOG4CXX_DEBUG(barlogger, "Exiting gas station search")</pre></div>
-
+
<p>
Calling the <tt>getLogger</tt> method
with the same name will
always return a reference to the exact
same logger object.
</p>
-
+
<p>
For example, in
</p>
-
+
<div>
<pre class="prettyprint linenums">
log4cxx::LoggerPtr x = log4cxx::Logger::getLogger("wombat");
log4cxx::LoggerPtr y =
log4cxx::Logger::getLogger("wombat");</pre></div>
-
+
<p>
<tt>x</tt> and <tt>y</tt> refer to
<i>exactly</i> the same logger object.
</p>
-
+
<p>
Thus, it is possible to configure a
logger and then to retrieve
the same instance somewhere else in the
code without passing around
@@ -703,14 +703,14 @@ log4cxx::LoggerPtr y = log4cxx::Logger::
instantiated after them.
</p>
-
+
<p>
Configuration of the log4cxx
environment is typically done at
application initialization. The
preferred way is by reading a
configuration file. This approach will
be discussed shortly.
</p>
-
+
<p>
Log4cxx makes it easy to name loggers
by <i>software
component</i>. This can be
accomplished by statically instantiating
@@ -724,7 +724,7 @@ log4cxx::LoggerPtr y = log4cxx::Logger::
loggers as desired.
</p>
-
+
<p>
Nevertheless, naming loggers after the
class where they are
located seems to be the best strategy
known so far.
@@ -732,10 +732,10 @@ log4cxx::LoggerPtr y = log4cxx::Logger::
</div>
</div>
-
+
<div class="section">
<h2>Appenders and Layouts<a name="Appenders_and_Layouts"></a></h2>
-
+
<p>
The ability to selectively enable or disable
logging requests based
on their logger is only part of the picture.
Log4cxx allows logging
@@ -749,10 +749,10 @@ log4cxx::LoggerPtr y = log4cxx::Logger::
daemons. It is also possible to log <a
href="apidocs/classlog4cxx_1_1_async_appender.html">asynchronously</a>.
</p>
-
+
<p>More than one appender can be attached to a logger.</p>
-
+
<p>
The <a
href="apidocs/classlog4cxx_1_1_logger.html#a7c0629acee8dbd1251474bea15d7c9e2">addAppender</a>
method adds an appender to a given logger.
@@ -771,15 +771,15 @@ log4cxx::LoggerPtr y = log4cxx::Logger::
<tt>false</tt>.
</p>
-
+
<p>The rules governing appender additivity are summarized below.</p>
-
+
<dl>
-
+
<dt><b>Appender Additivity</b></dt>
-
+
<dd>
The output of a log statement of logger
<i>C</i> will go to all the appenders
in <i>C</i> and its ancestors. This is
the meaning of the term "appender
@@ -792,108 +792,108 @@ log4cxx::LoggerPtr y = log4cxx::Logger::
</dd>
</dl>
-
+
<p>The table below shows an example:</p>
-
+
<table class="bodyTable" align="center" border="3" cellpadding="10">
-
+
<tr class="a">
-
+
<th>Logger Name </th>
-
+
<th>Added Appenders</th>
-
+
<th>Additivity Flag</th>
-
+
<th>Output Targets</th>
-
+
<th>Comment</th>
</tr>
-
+
<tr class="b">
-
+
<td>root</td>
-
+
<td>A1</td>
-
+
<td>not applicable</td>
-
+
<td>A1</td>
-
+
<td>
The root logger is anonymous
but can be accessed with the
log4cxx::Logger::getRootLogger() method. There is no default appender
attached to root.
</td>
</tr>
-
+
<tr class="a">
-
+
<td>x</td>
-
+
<td>A-x1, A-x2</td>
-
+
<td>true</td>
-
+
<td>A1, A-x1, A-x2</td>
-
+
<td>Appenders of "x" and root.</td>
</tr>
-
+
<tr class="b">
-
+
<td>x.y</td>
-
+
<td>none</td>
-
+
<td>true</td>
-
+
<td>A1, A-x1, A-x2</td>
-
+
<td>Appenders of "x" and root.</td>
</tr>
-
+
<tr class="a">
-
+
<td>x.y.z</td>
-
+
<td>A-xyz1</td>
-
+
<td>true</td>
-
+
<td>A1, A-x1, A-x2, A-xyz1</td>
-
+
<td>Appenders in "x.y.z", "x" and root.</td>
</tr>
-
+
<tr class="b">
-
+
<td>security</td>
-
+
<td>A-sec</td>
-
+
<td>
<span
class="activity-flag-highlight">false</span>
</td>
-
+
<td>A-sec</td>
-
+
<td>
No appender accumulation since
the additivity flag is set to <tt>false</tt>.
</td>
</tr>
-
+
<tr class="a">
-
+
<td>security.access</td>
-
+
<td>none</td>
-
+
<td>true</td>
-
+
<td>A-sec</td>
-
+
<td>
Only appenders of
"security" because the additivity flag in "security" is
set to <tt>false</tt>.
@@ -901,7 +901,7 @@ log4cxx::LoggerPtr y = log4cxx::Logger::
</tr>
</table>
-
+
<p>
More often than not, users wish to customize
not only the output
destination but also the output format. This is
accomplished by
@@ -911,7 +911,7 @@ log4cxx::LoggerPtr y = log4cxx::Logger::
to its destination.
</p>
-
+
<p>
The <a
href="apidocs/classlog4cxx_1_1_pattern_layout.html">PatternLayout</a>, part
of the standard log4cxx distribution, lets the
user specify the output
@@ -919,18 +919,18 @@ log4cxx::LoggerPtr y = log4cxx::Logger::
<tt>printf</tt> function.
</p>
-
+
<p>
For example, the PatternLayout with the
conversion pattern "%r [%t]
%-5p %c - %m%n" will output something akin
to:
</p>
-
+
<div>
<pre class="prettyprint linenums">
176 [main] INFO org.foo.Bar - Located nearest gas station.</pre></div>
-
+
<p>
The first field is the number of milliseconds
elapsed since the
start of the program. The second field is the
thread making the log
@@ -940,10 +940,10 @@ log4cxx::LoggerPtr y = log4cxx::Logger::
</p>
</div>
-
+
<div class="section">
<h2>Configuration<a name="Configuration"></a></h2>
-
+
<p>
Inserting log requests into the application
code requires a fair
amount of planning and effort. Observation
shows that approximately 4
@@ -953,7 +953,7 @@ log4cxx::LoggerPtr y = log4cxx::Logger::
manage these log statements without the need to
modify them manually.
</p>
-
+
<p>
The log4cxx environment is fully configurable
programmatically.
However, it is far more flexible to configure
log4cxx using
@@ -961,13 +961,13 @@ log4cxx::LoggerPtr y = log4cxx::Logger::
XML or in Java properties (key=value) format.
</p>
-
+
<p>
Let us give a taste of how this is done with
the help of an
imaginary application <tt>MyApp</tt> that uses
log4cxx.
</p>
-
+
<div>
<pre class="prettyprint linenums">
#include "com/foo/bar.h"
@@ -1004,7 +1004,7 @@ int main(int argc, char **argv)
return result;
}</pre></div>
-
+
<p>
<tt>MyApp</tt> begins by including log4cxx
headers. It
then defines a static logger variable with the
name <tt>MyApp</tt>
@@ -1012,13 +1012,13 @@ int main(int argc, char **argv)
class.
</p>
-
+
<p>
<tt>MyApp</tt> uses the <tt>Bar</tt> class
defined in header
file <tt>com/foo/bar.h</tt>.
</p>
-
+
<div>
<pre class="prettyprint linenums">
// file com/foo/bar.h
@@ -1035,7 +1035,7 @@ namespace com {
}
}</pre></div>
-
+
<div>
<pre class="prettyprint linenums">
// file bar.cpp
@@ -1050,7 +1050,7 @@ void Bar::doIt() {
LOG4CXX_DEBUG(logger, "Did it again!")
}</pre></div>
-
+
<p>
The invocation of the <a
href="apidocs/classlog4cxx_1_1_basic_configurator.html#a4f96a09e1372664e3556ce94ace4a70c">BasicConfigurator::configure</a>
method creates a rather simple log4cxx setup.
This method is hardwired
@@ -1060,25 +1060,25 @@ void Bar::doIt() {
to the pattern "%-4r [%t] %-5p %c %x -
%m%n".
</p>
-
+
<p>
Note that by default, the root logger is
assigned to
<tt>Level::getDebug()</tt>.
</p>
-
+
<p>
The output of MyApp is:
</p>
-
+
<div>
<pre class="prettyprint linenums">
0 [12345] INFO MyApp - Entering application.
36 [12345] DEBUG com.foo.Bar - Did it again!
51 [12345] INFO MyApp - Exiting application.</pre></div>
-
+
<p>
The previous example always outputs the same
log information.
Fortunately, it is easy to modify
<tt>MyApp</tt> so that the log
@@ -1086,7 +1086,7 @@ void Bar::doIt() {
version.
</p>
-
+
<div>
<pre class="prettyprint linenums">
// file MyApp2.cpp
@@ -1134,20 +1134,20 @@ int main(int argc, char **argv)
return result;
}</pre></div>
-
+
<p>
This version of <tt>MyApp</tt> instructs
<tt>PropertyConfigurator</tt> to parse a
configuration file and
set up logging accordingly.
</p>
-
+
<p>
Here is a sample configuration file that
results in exactly same
output as the previous
<tt>BasicConfigurator</tt> based example.
</p>
-
+
<div>
<pre class="prettyprint linenums">
# Set root logger level to DEBUG and its only appender to A1.
@@ -1160,19 +1160,19 @@ log4j.appender.A1=org.apache.log4j.Conso
log4j.appender.A1.layout=org.apache.log4j.PatternLayout
log4j.appender.A1.layout.ConversionPattern=%-4r [%t] %-5p %c %x -
%m%n</pre></div>
-
+
<p>
It can be noticed that the PropertyConfigurator
file format is the same as log4j.
</p>
-
+
<p>
Suppose we are no longer interested in seeing
the output of any
component belonging to the <tt>com::foo</tt>
package. The following
configuration file shows one possible way of
achieving this.
</p>
-
+
<div>
<pre class="prettyprint linenums">
log4j.rootLogger=DEBUG, A1
@@ -1185,18 +1185,18 @@ log4j.appender.A1.layout.ConversionPatte
# Print only messages of level WARN or above in the package com.foo.
<b>log4j.logger.com.foo=WARN</b></pre></div>
-
+
<p>
The output of <tt>MyApp</tt> configured with
this file is shown below.
</p>
-
+
<div>
<pre class="prettyprint linenums">
<b>2000-09-07 14:07:41,508</b> [12345] INFO MyApp - Entering application.
<b>2000-09-07 14:07:41,529</b> [12345] INFO MyApp - Exiting
application.</pre></div>
-
+
<p>
As the logger <tt>com.foo.Bar</tt> does not
have an assigned
level, it inherits its level from
<tt>com.foo</tt>, which
@@ -1206,12 +1206,12 @@ log4j.appender.A1.layout.ConversionPatte
request is suppressed.
</p>
-
+
<p>
Here is another configuration file that uses
multiple appenders.
</p>
-
+
<div>
<pre class="prettyprint linenums">
log4j.rootLogger=debug, <b>stdout, R</b>
@@ -1232,20 +1232,20 @@ log4j.appender.R.MaxBackupIndex=1
log4j.appender.R.layout=org.apache.log4j.PatternLayout
log4j.appender.R.layout.ConversionPattern=%p %t %c - %m%n</pre></div>
-
+
<p>
Calling the enhanced MyApp with the this
configuration file will
output the following on the console.
</p>
-
+
<div>
<pre class="prettyprint linenums">
INFO [12345] <b>(MyApp2.cpp:31)</b> - Entering application.
DEBUG [12345] (Bar.h:16) - Doing it again!
INFO [12345] (MyApp2.cpp:34) - Exiting application.</pre></div>
-
+
<p>
In addition, as the root logger has been
allocated a second
appender, output will also be directed to the
<tt>example.log</tt>
@@ -1254,7 +1254,7 @@ INFO [12345] (MyApp2.cpp:34) - Exiting a
automatically moved to <tt>example.log.1</tt>.
</p>
-
+
<p>
Note that to obtain these different logging
behaviors we did not
need to recompile code. We could just as easily
have logged to a UNIX
@@ -1265,10 +1265,10 @@ INFO [12345] (MyApp2.cpp:34) - Exiting a
</p>
</div>
-
+
<div class="section">
<h2>Default Initialization Procedure<a
name="Default_Initialization_Procedure"></a></h2>
-
+
<p>
The log4cxx library does not make any
assumptions about its
environment. In particular, there are no
default log4cxx
@@ -1277,16 +1277,16 @@ INFO [12345] (MyApp2.cpp:34) - Exiting a
automatically configure log4cxx.
</p>
-
+
<p>
The exact default initialization algorithm is
defined as follows:
</p>
-
+
<ol style="list-style-type: decimal">
-
+
<li>
-
+
<p>
Set the configurationOptionStr
string variable to the value of the
<b>LOG4CXX_CONFIGURATION</b>
environment variable if set, otherwise
@@ -1298,9 +1298,9 @@ INFO [12345] (MyApp2.cpp:34) - Exiting a
If configurationOptionStr has
not been set, then disable logging.
</p>
</li>
-
+
<li>
-
+
<p>
Unless a custom configurator is
specified using the
<b>LOG4CXX_CONFIGURATOR_CLASS</b> or <b>log4j.configuratorClass</b>
@@ -1315,10 +1315,10 @@ INFO [12345] (MyApp2.cpp:34) - Exiting a
</ol>
</div>
-
+
<div class="section">
<h2>Nested Diagnostic Contexts<a name="Nested_Diagnostic_Contexts"></a></h2>
-
+
<p>
Most real-world systems have to deal with
multiple clients
simultaneously. In a typical multithreaded
implementation of such a
@@ -1330,7 +1330,7 @@ INFO [12345] (MyApp2.cpp:34) - Exiting a
increases the management overhead of logging.
</p>
-
+
<p>
A lighter technique is to uniquely stamp each
log request initiated
from the same client interaction. Neil Harrison
described this method
@@ -1339,14 +1339,14 @@ INFO [12345] (MyApp2.cpp:34) - Exiting a
and F. Buschmann (Addison-Wesley, 1997).
</p>
-
+
<p>
To uniquely stamp each request, the
user pushes contextual information into the
NDC, the abbreviation of
<i>Nested Diagnostic Context</i>. The NDC class
is shown below.
</p>
-
+
<div>
<pre class="prettyprint linenums">
namespace log4cxx {
@@ -1365,7 +1365,7 @@ namespace log4cxx {
}
}</pre></div>
-
+
<p>
The NDC is managed per thread as a <i>stack</i>
of contextual
information. Note that all methods of the
<tt>log4cxx::NDC</tt>
@@ -1379,7 +1379,7 @@ namespace log4cxx {
approach commands extensive changes in the code.
</p>
-
+
<p>
To illustrate this point, let us take the
example of a servlet
delivering content to numerous clients. The
servlet can build the NDC
@@ -1394,7 +1394,7 @@ namespace log4cxx {
exercised during the client's request.
</p>
-
+
<p>
Nevertheless, some sophisticated applications,
such as virtual
hosting web servers, must log differently
depending on the virtual
@@ -1405,10 +1405,10 @@ namespace log4cxx {
</p>
</div>
-
+
<div class="section">
<h2>Performance<a name="Performance"></a></h2>
-
+
<p>
One of the often-cited arguments against
logging is its
computational cost. This is a legitimate
concern as even moderately
@@ -1417,21 +1417,21 @@ namespace log4cxx {
claims to be fast and flexible: speed first,
flexibility second.
</p>
-
+
<p>
The user should be aware of the following
performance issues.
</p>
-
+
<ol style="list-style-type: decimal">
-
+
<li>
-
+
<p>
<b>Logging performance when
logging is turned off.</b>
</p>
-
+
<p>
When logging is turned off
entirely or just for a set
of levels, the cost of a log
request consists of a method
@@ -1441,14 +1441,14 @@ namespace log4cxx {
</p>
</li>
-
+
<li>
-
+
<p>
<b>The performance of deciding
whether to log or not to log when logging is turned on.</b>
</p>
-
+
<p>
This is essentially the
performance of walking the logger
hierarchy. When logging is
turned on, log4cxx still needs to compare
@@ -1459,7 +1459,7 @@ namespace log4cxx {
ancestors.
</p>
-
+
<p>
There has been a serious effort
to make this hierarchy walk to
be as fast as possible. For
example, child loggers link only to
@@ -1471,20 +1471,20 @@ namespace log4cxx {
hierarchies.
</p>
-
+
<p>
The cost of walking the
hierarchy is typically 3
times slower than when logging
is turned off entirely.
</p>
</li>
-
+
<li>
-
+
<p>
<b>Actually outputting log
messages</b>
</p>
-
+
<p>
This is the cost of formatting
the log output and sending it to
its target destination. Here
again, a serious effort was made to
@@ -1495,10 +1495,10 @@ namespace log4cxx {
</ol>
</div>
-
+
<div class="section">
<h2>Conclusions<a name="Conclusions"></a></h2>
-
+
<p>
Apache Log4cxx is a popular logging package
written in C++. One of its
distinctive features is the notion of
inheritance in loggers. Using
@@ -1507,7 +1507,7 @@ namespace log4cxx {
logged output and minimize the cost of logging.
</p>
-
+
<p>
One of the advantages of the log4cxx API is its
manageability. Once
the log statements have been inserted into the
code, they can be
@@ -1518,7 +1518,7 @@ namespace log4cxx {
performance cost.
</p>
</div>
-
+
</td>
</tr>
