Author: ceki
Date: Wed Mar 14 22:32:01 2007
New Revision: 1429
Modified:
logback/trunk/logback-site/src/site/pages/manual/layouts.html
Log:
improved text, ongoing work
Modified: logback/trunk/logback-site/src/site/pages/manual/layouts.html
==============================================================================
--- logback/trunk/logback-site/src/site/pages/manual/layouts.html
(original)
+++ logback/trunk/logback-site/src/site/pages/manual/layouts.html Wed Mar
14 22:32:01 2007
@@ -22,6 +22,14 @@
<h1>Chapter 5: Layouts</h1>
+ <div class="quote">
+ <p>TCP implementations will follow a general principle of
+ robustness: be conservative in what you do, be liberal in what
+ you accept from others.
+ </p>
+ <p>-- JON POSTEL, RFC 793</p>
+ </div>
+
<script src="../templates/creative.js"></script>
<div class="highlight">
@@ -935,23 +943,26 @@
</tr>
</table>
- <p>Here are some examples of the format modifier truncation:</p>
+ <p>The table below list examples for format modifier
+ truncation. Please note that the brackets, i.e the pair of "[]"
+ characters, are not part of the output. They are used to delimit
+ the width of output.</p>
<table class="bodyTable" BORDER="0" CELLPADDING="8">
<th>Format modifier</th>
<th>Logger name</th>
- <th>Result</th>
- <tr class="a">
- <td align="center">[%-20.20logger]</td>
- <td align="center">main.Name</td>
- <td align="center"><pre>[main.Name
]</pre></td>
- </tr>
+ <th>Result</th>
<tr class="b">
<td align="center">[%20.20logger]</td>
<td align="center">main.Name</td>
<td align="center"><pre>[
main.Name]</pre></td>
</tr>
+ <tr class="a">
+ <td align="center">[%-20.20logger]</td>
+ <td align="center">main.Name</td>
+ <td align="center"><pre>[main.Name
]</pre></td>
+ </tr>
<tr class="a">
<td align="center">[%10.10logger]</td>
<td align="center">main.foo.foo.bar.Name</td>
@@ -964,18 +975,20 @@
</tr>
</table>
- <h3>Option handling</h3>
+ <h3>Options</h3>
<p>
- A conversion specifier can be followed by options
between
- braces. We have already seen some of the
- possibilities offered by logback's option handling
with, for
- example, the MDC conversion specifier:
+ A conversion specifier can be followed by options. The
are
+ always declared between braces. We have already seen
some of the
+ possibilities offered by options, for instance in
conjunction
+ with the MDC conversion specifier, as in:
<em>%mdc{someKey}</em>.
</p>
- <p>A conversion specifier might have more than one options. For
example,
- a conversion specifier that uses evaluators, which we will
cover very soon,
- simply adds the evaluator names to the option list, as shown
below:</p>
+
+ <p>A conversion specifier might have more than one option. For
+ example, a conversion specifier that makes use of evaluators,
+ which will be covered soon, may add evaluator names to the option
+ list, as shown below:</p>
<div class="source"><pre>
<appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
@@ -986,43 +999,30 @@
</appender></pre></div>
- XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
+ <h3>Evaluators</h3>
- <h4>Evaluators</h4>
- <p>
- Another use case for adding options to a conversion
- specifier is when
- <code>PatternLayout</code>
- is used with
- <a
href="../xref/ch/qos/logback/core/boolex/EventEvaluator.html">
- <code>EventEvaluator</code></a> objects.
- </p>
- <p>
- <code>EventEvaluator</code> objects
- have the responsability to check wether a given event
- matches a given criteria.
- </p>
- <p>
- Let's look at an example using
- <code>EventEvaluator</code> objects.
- The following configuration file outputs the logging
- events to the console, displaying date, thread, level,
- message and caller data.
- </p>
- <p>
- Since displaying the caller data of a logging event is
rather
- expensive, this information will be displayed only when
the
- logging request comes from a specific logger, and whose
- message contains a certain string. By doing that, we
make
- sure that only the specific logging requests will have
- their caller information generated and displayed,
without
- penalizing application performance.
+ <p>As mentioned above, option lists come in handy when a
+ conversion specifier is required to behave dynamically based on
+ one or more
+ <a
href="../xref/ch/qos/logback/core/boolex/EventEvaluator.html">
+ <code>EventEvaluator</code></a> objects.
+ <code>EventEvaluator</code> objects have the responsibility to
+ determine whether a given logging event matches the criteria of
the
+ evaluator.
+ </p>
+
+ <p>Let us review an example with <code>EventEvaluator</code>
+ objects. The following configuration file outputs the logging
+ events to the console, displaying date, thread, level, message and
+ caller data. Given that extracting the caller data of a logging
+ event is on expensive side, we will do so only when the logging
+ request originates from a specific logger, and whose message
+ contains a certain string. Thus, we make sure that only specific
+ logging requests will have their caller information generated and
+ displayed. In other cases, where the caller data is superfluous,
+ we will not penalize application performance.
</p>
- <p>
- Here is how to configure logback to behave like we
- described:
- </p>
<em>
Example 5.2: Sample usage of EventEvaluators
(logback-examples/src/main/java/chapter5/callerEvaluatorConfig.xml)
@@ -1045,14 +1045,19 @@
<appender-ref ref="STDOUT" />
</root>
</configuration></pre></div>
- <p>Please note that the & value cannot be written like one
would do in a java
- class, because of XML encoding rules.</p>
- <p>Let us test this configuration with the following code.</p>
- <em>
+
+ <p>Due to XML encoding rules, the & character cannot be
+ written as is, and needs to be escaped as &amp;.</p>
+
+ <p>The above configuration file is designed to be accompanied by
+ the following custom-tailored code.</p>
+
+ <p><em>
Example 5.2: Sample usage of EventEvaluators
<a href="../xref/chapter5/CallerEvaluatorExample.html">
(logback-examples/src/main/java/chapter5/CallerEvaluatorExample.java)</a>
</em>
+ </p>
<div class="source"><pre>package chapter5;
import org.slf4j.Logger;
@@ -1087,51 +1092,58 @@
}
}</pre></div>
<p>
- The above application does nothing too fancy. Five
logging
- requests are issued, the third one being different from
the
- others.
+ The <em>CallerEvaluatorExample</em> application does
nothing particularly
+ fancy. Five logging requests are issued, the third one
being
+ different from the others.
</p>
<p>
- When a logging request is sent, the corresponding
logging event
- will pass through the evaluation process. Here, the
third
- request will match the evaluation criteria, causing its
caller
- data to be displayed.
+ When a logging request is issued, the corresponding
logging
+ event goes through the evaluation process. The third
request
+ matches the evaluation criteria, causing its caller
data to be
+ displayed.
</p>
+
<p>
Here is the output of the
<code>CallerEvaluatorExample</code>
class.
</p>
+
<div class="source"><pre>0 [main] DEBUG - I know me 0
0 [main] DEBUG - I know me 1
0 [main] DEBUG - I know me 2
0 [main] DEBUG - who calls thee?
Caller+0 at
chapter5.CallerEvaluatorExample.main(CallerEvaluatorExample.java:28)
-
0 [main] DEBUG - I know me 4</pre></div>
- <p>One can change the expression to match a real world
- situation. An expression testing logger name and request level
- could also be meaningful: all logging requests of level
- <em>WARN</em> and up, coming from a sensible part of an
- application like a financial transaction module, would have
their
- caller data displayed.
+ <p>One can change the expression to correspond a real world
+ scenario. For instance, one could combine the logger name and
+ request level. Thus, logging requests of level <em>WARN</em> and
+ up, originating from a sensitive part of an application, e.g. a
+ financial transaction module, would have their caller data
+ displayed.
</p>
<p><b>Important:</b> With the <em>caller</em> conversion
specifier, the data is displayed when <em>the expression
evaluates
to <b>true</b>.</em></p>
- <p>Now, let us look at a different situation. When exceptions
are
+ <p>Let us consider at a different situation. When exceptions are
included in a logging request, their stack trace is usually
displayed. However, in some cases, one might want to supress the
- stack trace of specific exception.
+ stack trace of some specific exception.
</p>
- <p>The java code shown below creates five log requests, each one
- with an exception. However, we do not want to have the stack
trace
- of the third request to be output.</p>
+ <p>The java code shown below creates five log requests, each
with
+ an exception. However, it so happends that we do not wish the
+ stack trace of the third request to be output.</p>
+ <p><em>
+ Example 5.2: Sample usage of EventEvaluators
+ <a
href="../xref/chapter5/ExceptionEvaluatorExample.html">
+
(logback-examples/src/main/java/chapter5/ExceptionEvaluatorExample.java)</a>
+ </em>
+ </p>
<div class="source"><pre>package chapter5;
import org.slf4j.Logger;
@@ -1166,7 +1178,8 @@
}
}</pre></div>
- <p>The following configuration will allow that.</p>
+ <p>The following configuration will supress the stack trace of
the
+ third logging request.</p>
<em>
Example 5.3: Sample usage of EventEvaluators
(logback-examples/src/main/java/chapter5/exceptionEvaluatorConfig.xml)
@@ -1193,31 +1206,38 @@
</root>
</configuration></pre></div>
- <p>
- With this configuration, each time an instance of the
- <em>chapter5.TestException</em>
- is included within a logging request, no stack trace
will be displayed.
+ <p>With this configuration, each time an instance of the
+ <em>chapter5.TestException</em> is included within a logging
+ request, the stack trace will be suppressed.
</p>
- <p><b>Important:</b> With the <b><em>%ex</em></b> conversion
specifier, the data is
- displayed when <em>the expression evaluates to
<b>false</b>.</em></p>
+
+ <p><b>Important:</b> With the <b><em>%ex</em></b> conversion
+ specifier, the stack trace is displayed when <em>the expression
+ evaluates to <b>false</b>.</em></p>
<h3>Creating a custom conversion specifier</h3>
- <p>We've seen up to here quite a lot of possibilities with
conversion specifier and
- <code>PatternLayout</code> objects. But what if somebody wants
to make her own conversion
- specifier?</p>
-
- <p>In that case, two steps are needed.</p>
-
- <p>First, one must implement her own <code>Converter</code>
- class. <a
href="../xref/ch/qos/logback/core/pattern/Converter.html">
- <code>Converter</code></a> objects are responsible to extract a
specific information out of
- a <code>LoggingEvent</code>. When <em>%logger</em> is used, a
- <a
href="../xref/ch/qos/logback/classic/pattern/LoggerConverter.html">
- <code>LoggerConverter</code></a>
- is called to extract the name of the logger from the
<code>LoggingEvent</code>.</p>
+
+ <p>Up to this point we have presented the built-inconversion
+ specifiers of <code>PatternLayout</code>. But it is also
possible
+ to use a conversion specifier of your own making.</p>
+
+ <p>Building a custom conversion specifier consists of two steps.
+ </p>
- <p>Let us say that our customized <code>Converter</code> will
output the level of the logging
- event, colored following ANSI rules. Here is the necessary
implementation:</p>
+ <p>First, you must sub-class the <code>Converter</code> class.
<a
+ href="../xref/ch/qos/logback/core/pattern/Converter.html">
+ <code>Converter</code></a> objects are responsible for
extracting
+ information out of <code>LoggingEvent</code> objects and
returning
+ it as String. For example, the
+ <a
href="../xref/ch/qos/logback/classic/pattern/LoggerConverter.html">
+ <code>LoggerConverter</code></a>, the converter underlying the
+ %logger conversion word, extracts the name of the logger from
the
+ <code>LoggingEvent</code> and returns it as a String. It might
+ abbreviate the logger name in the process.</p>
+
+ <p>Let us say that our customized <code>Converter</code> colors
+ the level of the logging event, according to ANSI terminal
+ conventions. Here is a possible implementation:</p>
<em> Example 5.4: Sample Converter Example
<a href="../xref/chapter5/MySampleConverter.html">
@@ -1261,14 +1281,19 @@
}
</pre></div>
- <p>This implementation is quite straightforward. The
<code>MySampleConverter</code> class
- extends <code>ClassicConverter</code>, and implements the
<code>convert</code> method.
- In that method, all it has to do is return the appropriate
information.
+
+java chapter5.SampleLogging src/main/java/chapter5/mySampleConverterConfig.xml
+
+ <p>This implementation is relatively straightforward. The
+ <code>MySampleConverter</code> class extends
+ <code>ClassicConverter</code>, and implements the
+ <code>convert</code> method where it returns a level string
+ decorated with ANSI coloring codes.
</p>
- <p>The second step, once the <code>Converter</code> class done,
is to let logback know about
- the new <code>Converter</code>. For this task, we just need to
declare the new
- conversion word in the configuration file, as shown below:</p>
+ <p>In the second step, we must let logback know about the new
+ <code>Converter</code>. For this purpose, we need to declare the
+ new conversion word in the configuration file, as shown
below:</p>
<em> Example 5.4: Sample Converter Example
(src/main/java/chapter5/mySampleConverterConfig.xml)</em>
<div class="source"><pre><configuration>
@@ -1288,17 +1313,37 @@
</root>
</configuration></pre></div>
- <p>In this configuration file, once the new conversion word has
been declared, we
- just use it within a <code>PatternLayout</code> pattern
element, as if
- our custom conversion word had always been here.</p>
-
- <p>The intersted reader might want to take a look at other
<code>Converter</code> implementations
- like
+ <p>In this configuration file, once the new conversion word has
+ been declared, we can refert to it within a
+ <code>PatternLayout</code> pattern, as if the custom conversion
+ word had always been here.</p>
+
+ <p>Given that ANSI terminal codes do not work on Windows, you can
+ view the results on non-Windows platforms such as Linux or
+ Mac. The following command:</p>
+
+ <div class="source">java chapter5.SampleLogging
src/main/java/chapter5/mySampleConverterConfig.xml </div>
+
+ <p>should yield:</p>
+
+<div class="source">0 [main] DEBUG - Everything's going well
+3 [main] <span class="red">ERROR</span> - maybe not quite... </div>
+
+XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXxxxx
+
+ <p>Please note that the string "ERROR" is highlighted in red,
+ which is basically the whole point of the exercise.</p>
+
+ <p>The intersted reader might want to take a look at other
+ <code>Converter</code> implementations such as
<a
href="../xref/ch/qos/logback/classic/pattern/MDCConverter.html">
- <code>MDCConverter</code></a> to learn how to implement more
complex behaviours, involving
- the use of options, in her custom <code>Converter</code>
objects.
+ <code>MDCConverter</code></a> to learn how to implement more
+ complex behaviour, such as option handling.
</p>
+
+
+
<a name="ClassicHTMLLayout"></a>
<h3>HTMLLayout</h3>
<p><a
href="../xref/ch/qos/logback/classic/html/HTMLLayout.html">
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