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| |
| <a name="top"></a> |
| <div class="section"><h2>Custom Log Levels<a name="Custom_Log_Levels"></a></h2> |
| <p> |
| Log4J 2 supports custom log levels. The <tt>Level.forName()</tt> method creates a new |
| level for the specified name. By calling the Logger.log() method and passing this |
| custom log level you can log messages at this level: |
| </p> |
| <div class="prettyprint"><pre> |
| final Logger logger = LogManager.getLogger(); |
| final Level VERBOSE = Level.forName("VERBOSE", 550); |
| |
| logger.log(VERBOSE, "a verbose message"); |
| logger.log(VERBOSE, "another message");</pre></div> |
| <p>When defining a custom log level, the <tt>intLevel</tt> parameter (550 in the example above) determines |
| where the custom level exists in relation to the standard levels built-in to Log4J 2. |
| For reference, the table below shows the <tt>intLevel</tt> of the built-in log levels. |
| </p> |
| <table border="0" class="bodyTable" style="width: 30%"><caption align="top">Standard log levels built-in to Log4J</caption> |
| |
| <tr class="a"> |
| <th>Standard Level</th> |
| <th>intLevel</th> |
| </tr> |
| <tr class="b"> |
| <td>OFF</td> |
| <td align="right">0</td> |
| </tr> |
| <tr class="a"> |
| <td>FATAL</td> |
| <td align="right">100</td> |
| </tr> |
| <tr class="b"> |
| <td>ERROR</td> |
| <td align="right">200</td> |
| </tr> |
| <tr class="a"> |
| <td>WARN</td> |
| <td align="right">300</td> |
| </tr> |
| <tr class="b"> |
| <td>INFO</td> |
| <td align="right">400</td> |
| </tr> |
| <tr class="a"> |
| <td>DEBUG</td> |
| <td align="right">500</td> |
| </tr> |
| <tr class="b"> |
| <td>TRACE</td> |
| <td align="right">600</td> |
| </tr> |
| <tr class="a"> |
| <td>ALL</td> |
| <td align="right"><tt>Integer.MAX_VALUE</tt></td> |
| </tr> |
| </table> |
| |
| <a name="StandardLoggerInterface"></a> |
| <div class="section"><h3>Convenience Methods for the Built-in Log Levels<a name="Convenience_Methods_for_the_Built-in_Log_Levels"></a></h3> |
| <p> |
| The built-in log levels have a set of convenience methods on the Logger |
| interface that makes them easier to use. For example, the Logger interface |
| has fourteen <tt>debug()</tt> methods that support the DEBUG level: |
| </p> |
| <div class="prettyprint"><pre> |
| // convenience methods for the built-in DEBUG level |
| debug(Marker, Message) |
| debug(Marker, Message, Throwable) |
| debug(Marker, Object) |
| debug(Marker, Object, Throwable) |
| debug(Marker, String) |
| debug(Marker, String, Object...) |
| debug(Marker, String, Throwable) |
| debug(Message) |
| debug(Message, Throwable) |
| debug(Object) |
| debug(Object, Throwable) |
| debug(String) |
| debug(String, Object...) |
| debug(String, Throwable)</pre></div> |
| <p> |
| Similar methods exist for the other built-in levels. |
| </p> |
| <p>It would be nice to have the same ease of use with custom levels, |
| so that after declaring a custom VERBOSE level, we could |
| use code like this: |
| </p> |
| <div class="prettyprint"><pre> |
| logger.verbose("a verbose message"); // no need to pass the VERBOSE level as a parameter |
| logger.verbose("another message");</pre></div> |
| </div> |
| <a name="AddingOrReplacingLevels"></a> |
| <div class="section"><h3>Adding or Replacing Log Levels<a name="Adding_or_Replacing_Log_Levels"></a></h3> |
| <p>In the above example, a convenience method was <i>added</i> to the Logger interface, |
| in addition to the existing trace(), debug(), info(), ... methods for the built-in log levels. |
| </p> |
| <p>There is another use case, Domain Specific Language loggers, where we want to <i>replace</i> |
| the existing trace(), debug(), info(), ... methods with all-custom methods. |
| </p> |
| <p> |
| For example, for medical devices we could have only <tt>critical()</tt>, <tt>warning()</tt>, |
| and <tt>advisory()</tt> methods. |
| Another example could be a game that has only <tt>defcon1()</tt>, <tt>defcon2()</tt>, |
| and <tt>defcon3()</tt> levels. |
| </p> |
| <p> |
| If it were possible to hide existing log levels, users could customize the |
| Logger interface to match their requirements. Some people may not want to |
| have a FATAL or a TRACE level, for example. They would like to be able to |
| create a custom Logger that only has debug(), info(), warn() and error() methods. |
| </p> |
| </div> |
| <a name="CustomLoggers"></a> |
| <div class="section"><h3>Generating Source Code for a Custom Logger Wrapper<a name="Generating_Source_Code_for_a_Custom_Logger_Wrapper"></a></h3> |
| <p> |
| Common Log4J usage is to get an instance of the <tt>Logger</tt> interface from the |
| <tt>LogManager</tt> and call the methods on this interface. |
| However, the custom log Levels are not known in advance, so Log4J cannot provide |
| an interface with convenience methods for these custom log Levels. |
| </p> |
| <p> |
| To solve this, Log4J ships with a tool that generates source code for a |
| Logger wrapper. The generated wrapper class has convenience methods for each |
| custom log level, making custom levels just as easy to use as the built-in levels. |
| </p> |
| <p> |
| There are two flavors of wrappers: ones that <i><b>extend</b></i> the Logger |
| API (adding methods to the built-in levels) and ones that <i><b>customize</b></i> |
| the Logger API (replacing the built-in methods). |
| </p> |
| <p>When generating the source code for a wrapper class, you need to specify:</p> |
| <ul> |
| <li>the fully qualified name of the class to generate |
| </li> |
| <li>the list of custom levels to support and their <tt>intLevel</tt> relative strength |
| </li> |
| <li>whether to extend <tt>Logger</tt> (and keep the existing built-in methods) |
| or have only methods for the custom log levels |
| </li> |
| </ul> |
| <p>You would then include the generated source code in the project |
| where you want to use custom log levels.</p> |
| </div> |
| <a name="ExampleUsage"></a> |
| <div class="section"><h3>Example Usage of a Generated Logger Wrapper<a name="Example_Usage_of_a_Generated_Logger_Wrapper"></a></h3> |
| <p> |
| Here is an example of how one would use a generated logger wrapper with |
| custom levels DIAG, NOTICE and VERBOSE: |
| </p> |
| <div class="prettyprint linenums"><pre> |
| // ExtLogger is a generated logger wrapper |
| import com.mycompany.myproject.ExtLogger; |
| |
| public class MyService { |
| // instead of Logger logger = LogManager.getLogger(MyService.class): |
| private static final ExtLogger logger = ExtLogger.create(MyService.class); |
| |
| public void someMethod() { |
| // ... |
| logger.trace("the built-in TRACE level"); |
| logger.verbose("a custom level: a VERBOSE message"); |
| logger.debug("the built-in DEBUG level"); |
| logger.notice("a custom level: a NOTICE message"); |
| logger.info("the built-in INFO level"); |
| logger.diag("a custom level: a DIAG message"); |
| logger.warn("the built-in WARN level"); |
| logger.error("the built-in ERROR level"); |
| logger.fatal("the built-in FATAL level"); |
| // ... |
| } |
| ... |
| }</pre></div> |
| </div> |
| <a name="CodeGen"></a> |
| <div class="section"><h3>Generating Extended Loggers<a name="Generating_Extended_Loggers"></a></h3> |
| <p> |
| Use the following command to generate a logger wrapper that adds methods to the built-in ones: |
| </p> |
| <div class="prettyprint"><pre> |
| java -cp log4j-core-2.0.2.jar org.apache.logging.log4j.core.tools.Generate$ExtendedLogger \ |
| com.mycomp.ExtLogger DIAG=350 NOTICE=450 VERBOSE=550 > com/mycomp/ExtLogger.java</pre></div> |
| <p> |
| This will generate source code for a logger wrapper that has the convenience methods |
| for the built-in levels <i>as well as</i> the specified custom levels. The tool prints the |
| generated source code to the console. |
| By appending " > <i>filename</i>" the output can be redirected to a file. |
| </p> |
| </div> |
| <div class="section"><h3>Generating Custom Loggers<a name="Generating_Custom_Loggers"></a></h3> |
| <p> |
| Use the following command to generate a logger wrapper that hides the built-in levels and has only custom levels: |
| </p> |
| <div class="prettyprint"><pre> |
| java -cp log4j-core-2.0.2.jar org.apache.logging.log4j.core.tools.Generate$CustomLogger \ |
| com.mycomp.MyLogger DEFCON1=350 DEFCON2=450 DEFCON3=550 > com/mycomp/MyLogger.java</pre></div> |
| <p> |
| This will generate source code for a logger wrapper that <i>only</i> has convenience |
| methods for the specified custom levels, <i>not</i> for the built-in levels. |
| The tool prints the generated source code to the console. |
| By appending " > <i>filename</i>" the output can be redirected to a file. |
| </p> |
| </div> |
| </div> |
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