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Needle Version: <strong>1.3.0</strong><br />
Manual Last Updated: <strong>2005-12-24 15:20 UTC</strong>
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Logging
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<h1>7. Logging</h1>
<h2>
<a name="s1"></a>
7.1. Overview
</h2>
<div class="section">
<p>Logging is a pretty common activity in many applications. Because it is so common, Needle provides a powerful framework for logging messages in a consistent manner.</p>
<p>Needle’s logging framework is built on top of the standard Ruby <code>Logger</code> library. However, it extends that library to add additional functionality, including customizable message formats and a centralized location for obtaining logger instances.</p>
<p>This centralized location is the LogFactory.</p>
</div>
<h2>
<a name="s2"></a>
7.2. LogFactory
</h2>
<div class="section">
<p>The LogFactory is available as a service, so that any component that needs a logger instance can gain easy access to one. The factory’s service name is <code>:logs</code>.</p>
<div class='figure'>
<span class='caption'>Accessing the LogFactory service [ruby]</span>
<div class='body'><link rel='stylesheet' type='text/css' href='stylesheets/ruby.css' /><div class='ruby'><pre><span class="ident">factory</span> <span class="punct">=</span> <span class="ident">reg</span><span class="punct">.</span><span class="ident">logs</span></pre></div></div></div>
<p>You obtain logger instances from the factory by passing a logger name to <code>#get</code>:</p>
<div class='figure'>
<span class='caption'>Getting a named logger instance [ruby]</span>
<div class='body'><link rel='stylesheet' type='text/css' href='stylesheets/ruby.css' /><div class='ruby'><pre><span class="ident">logger</span> <span class="punct">=</span> <span class="ident">reg</span><span class="punct">.</span><span class="ident">logs</span><span class="punct">.</span><span class="ident">get</span> <span class="punct">"</span><span class="string">a logger name</span><span class="punct">"</span></pre></div></div></div>
<p>Subsequent calls to <code>#get</code> will return the same logger instance for the given logger name.</p>
<h3>Loggers for Services</h3>
<p>Typically, you’ll use this to assign a logger instance to a service when it is constructed. In that case, the name of the logger is the fully-qualified name of the service:</p>
<div class='figure'>
<span class='caption'>Getting a logger for a service [ruby]</span>
<div class='body'><table border='0' cellpadding='0' cellspacing='0'><tr><td class='lineno'>1<br />2<br />3<br /></td><td width='100%'><link rel='stylesheet' type='text/css' href='stylesheets/ruby.css' /><div class='ruby'><pre><span class="ident">reg</span><span class="punct">.</span><span class="ident">register</span><span class="punct">(</span> <span class="symbol">:foo</span> <span class="punct">)</span> <span class="keyword">do</span> <span class="punct">|</span><span class="ident">c</span><span class="punct">,</span><span class="ident">p</span><span class="punct">|</span>
<span class="constant">Foo</span><span class="punct">.</span><span class="ident">new</span><span class="punct">(</span> <span class="ident">c</span><span class="punct">.</span><span class="ident">logs</span><span class="punct">.</span><span class="ident">get</span><span class="punct">(</span> <span class="ident">p</span><span class="punct">.</span><span class="ident">fullname</span> <span class="punct">)</span> <span class="punct">)</span>
<span class="keyword">end</span></pre></div></td></tr></table></div></div>
<p>As a convenience, if the value passed to <code>#get</code> responds to either <code>fullname</code> or <code>name</code>, the return value of that message will be used as the name. Thus, you can do the following:</p>
<div class='figure'>
<span class='caption'>Getting a logger for a service (simplified) [ruby]</span>
<div class='body'><table border='0' cellpadding='0' cellspacing='0'><tr><td class='lineno'>1<br />2<br />3<br /></td><td width='100%'><link rel='stylesheet' type='text/css' href='stylesheets/ruby.css' /><div class='ruby'><pre><span class="ident">reg</span><span class="punct">.</span><span class="ident">register</span><span class="punct">(</span> <span class="symbol">:foo</span> <span class="punct">)</span> <span class="keyword">do</span> <span class="punct">|</span><span class="ident">c</span><span class="punct">,</span><span class="ident">p</span><span class="punct">|</span>
<span class="constant">Foo</span><span class="punct">.</span><span class="ident">new</span><span class="punct">(</span> <span class="ident">c</span><span class="punct">.</span><span class="ident">logs</span><span class="punct">.</span><span class="ident">get</span><span class="punct">(</span> <span class="ident">p</span> <span class="punct">)</span> <span class="punct">)</span>
<span class="keyword">end</span></pre></div></td></tr></table></div></div>
<p>As a further convenience, there is a <code>:log_for</code> service that is parameterized. Just pass the name of the log to retreive (or the service point instance) and it will return the log handle directly:</p>
<div class='figure'>
<span class='caption'>Getting a logger for a service (simplified further) [ruby]</span>
<div class='body'><table border='0' cellpadding='0' cellspacing='0'><tr><td class='lineno'>1<br />2<br />3<br /></td><td width='100%'><link rel='stylesheet' type='text/css' href='stylesheets/ruby.css' /><div class='ruby'><pre><span class="ident">reg</span><span class="punct">.</span><span class="ident">register</span><span class="punct">(</span> <span class="symbol">:foo</span> <span class="punct">)</span> <span class="keyword">do</span> <span class="punct">|</span><span class="ident">c</span><span class="punct">,</span><span class="ident">p</span><span class="punct">|</span>
<span class="constant">Foo</span><span class="punct">.</span><span class="ident">new</span><span class="punct">(</span> <span class="ident">c</span><span class="punct">.</span><span class="ident">log_for</span><span class="punct">(</span> <span class="ident">p</span> <span class="punct">)</span> <span class="punct">)</span>
<span class="keyword">end</span></pre></div></td></tr></table></div></div>
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<h2>
<a name="s3"></a>
7.3. Configuration
</h2>
<div class="section">
<p>You can configure the LogFactory when you create the registry by passing a hash as the <code>:logs</code> option to <code>Registry.new</code>. The hash may have the following properties:</p>
<table>
<tr>
<td style="vertical-align:top;"><code>:device</code></td>
<td>Should refer to an IO or pseudo-IO object that will receive <code>#write</code> and <code>#close</code> messages.</td>
</tr>
<tr>
<td style="vertical-align:top;"><code>:filename</code></td>
<td>The name of the file to write log messages to.</td>
</tr>
<tr>
<td style="vertical-align:top;"><code>:roll_age</code></td>
<td>The number of days before the log should be rolled.</td>
</tr>
<tr>
<td style="vertical-align:top;"><code>:roll_frequency</code></td>
<td>Either ‘daily’, ‘weekly’, or ‘monthly’, indicating how often the log should be rolled.</td>
</tr>
<tr>
<td style="vertical-align:top;"><code>:roll_size</code></td>
<td>The maximum size that a log file may grow to before it is rolled.</td>
</tr>
<tr>
<td style="vertical-align:top;"><code>:default_date_format</code></td>
<td>A <code>strftime</code>-formatted string to use for formatting message dates and times.</td>
</tr>
<tr>
<td style="vertical-align:top;"><code>:default_message_format</code></td>
<td>A printf-styled format string to use when formatting messages. It’s format is reminiscent of Log4r, but differs in some options. See the <span class="caps">API</span> documentation for Needle::Logger for details.</td>
</tr>
<tr>
<td style="vertical-align:top;"><code>:default_level</code></td>
<td>One of <code>:debug</code>, <code>:info</code>, <code>:warn</code>, <code>:error</code>, or <code>:fatal</code>, indicating the default level of logging detail to use.</td>
</tr>
<tr>
<td style="vertical-align:top;"><code>:levels</code></td>
<td>Another hash of pattern/level or pattern/hash pairs, where the pattern is a string describing the logger name (or names) that it matches. If the corresponding value of a key is a symbol or a string, then it describes the logging level to use for loggers that match it. If the value is a hash, then it may contain <code>:level</code>, <code>:date_format</code>, or <code>:message_format</code> keys that apply to matching logs.</td>
</tr>
</table>
<p>By default, the filename is ”./needle.log”, and the roll_size is one megabyte. The default level is <code>:debug</code>. If you wanted to specify a different filename and default level of <code>:warn</code>, you could do:</p>
<div class='figure'>
<span class='caption'>Configuring the loggers [ruby]</span>
<div class='body'><table border='0' cellpadding='0' cellspacing='0'><tr><td class='lineno'>1<br />2<br />3<br />4<br />5<br /></td><td width='100%'><link rel='stylesheet' type='text/css' href='stylesheets/ruby.css' /><div class='ruby'><pre><span class="ident">reg</span> <span class="punct">=</span> <span class="constant">Needle</span><span class="punct">::</span><span class="constant">Registry</span><span class="punct">.</span><span class="ident">new</span><span class="punct">(</span>
<span class="symbol">:logs</span> <span class="punct">=></span> <span class="punct">{</span>
<span class="symbol">:filename</span> <span class="punct">=></span> <span class="punct">"</span><span class="string">./my-app.log</span><span class="punct">",</span>
<span class="symbol">:default_level</span> <span class="punct">=></span> <span class="symbol">:warn</span> <span class="punct">}</span>
<span class="punct">)</span></pre></div></td></tr></table></div></div>
<p>Alternatively, you can easily put the logging configuration in a <span class="caps">YAML</span> file and read it in, like so:</p>
<div class='figure'>
<span class='caption'>Configuring the loggers from a YAML file [ruby]</span>
<div class='body'><table border='0' cellpadding='0' cellspacing='0'><tr><td class='lineno'>1<br />2<br />3<br />4<br /></td><td width='100%'><link rel='stylesheet' type='text/css' href='stylesheets/ruby.css' /><div class='ruby'><pre><span class="ident">require</span> <span class="punct">'</span><span class="string">yaml</span><span class="punct">'</span>
<span class="ident">reg</span> <span class="punct">=</span> <span class="constant">Needle</span><span class="punct">::</span><span class="constant">Registry</span><span class="punct">.</span><span class="ident">new</span><span class="punct">(</span>
<span class="symbol">:logs</span> <span class="punct">=></span> <span class="constant">YAML</span><span class="punct">.</span><span class="ident">load</span><span class="punct">(</span> <span class="constant">File</span><span class="punct">.</span><span class="ident">read</span><span class="punct">(</span> <span class="punct">"</span><span class="string">log-conf.yml</span><span class="punct">"</span> <span class="punct">)</span> <span class="punct">)</span>
<span class="punct">)</span></pre></div></td></tr></table></div></div>
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