动态改变log4j的级别(level)

朱雀 2022-07-14 01:27 54阅读 0赞

转载：http://stackoverflow.com/questions/4598702/dynamically-changing-log4j-log-level

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     <p style="margin-top:0px; margin-bottom:1em; padding-top:0px; padding-bottom:0px; border:0px; clear:both"> Changing the log level is simple; modifying other portions of the configuration will pose a more in depth approach.</p> 
     <pre style="margin-top:0px; margin-bottom:1em; padding:5px; border:0px; font-size:13px; width:auto; max-height:600px; overflow:auto; font-family:Consolas,Menlo,Monaco,&quot;Lucida Console&quot;,&quot;Liberation Mono&quot;,&quot;DejaVu Sans Mono&quot;,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,monospace,sans-serif; background-color:rgb(239,240,241); word-wrap:normal"><code style="margin:0px; padding:0px; border:0px; font-family:Consolas,Menlo,Monaco,&quot;Lucida Console&quot;,&quot;Liberation Mono&quot;,&quot;DejaVu Sans Mono&quot;,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,monospace,sans-serif; white-space:inherit">LogManager.getRootLogger().setLevel(Level.DEBUG);
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     <p style="margin-top:0px; margin-bottom:1em; padding-top:0px; padding-bottom:0px; border:0px; clear:both"> The changes are permanent through the life cyle of the&nbsp;<code style="margin:0px; padding:1px 5px; border:0px; font-size:13px; font-family:Consolas,Menlo,Monaco,&quot;Lucida Console&quot;,&quot;Liberation Mono&quot;,&quot;DejaVu Sans Mono&quot;,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,monospace,sans-serif; background-color:rgb(239,240,241); white-space:pre-wrap">Logger</code>. On reinitialization the configuration will be read and used as setting the level at runtime does not persist the level change.</p> 
     <p style="margin-top:0px; margin-bottom:1em; padding-top:0px; padding-bottom:0px; border:0px; clear:both"> <span style="margin:0px; padding:0px; border:0px">UPDATE:</span>&nbsp;If you are using Log4j 2 you should remove the calls to&nbsp;<code style="margin:0px; padding:1px 5px; border:0px; font-size:13px; font-family:Consolas,Menlo,Monaco,&quot;Lucida Console&quot;,&quot;Liberation Mono&quot;,&quot;DejaVu Sans Mono&quot;,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,monospace,sans-serif; background-color:rgb(239,240,241); white-space:pre-wrap">setLevel</code>&nbsp;per the&nbsp;<a href="http://logging.apache.org/log4j/2.x/manual/migration.html" style="margin:0px; padding:0px; border:0px; color:rgb(0,89,153); text-decoration:none" rel="nofollow">documentation</a>as this can be achieved via implementation classes.</p> 
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      <p style="margin-top:0px; margin-bottom:0px; padding-top:0px; padding-bottom:0px; border:0px; clear:both"> Calls to logger.setLevel() or similar methods are not supported in the API. Applications should remove these. Equivalent functionality is provided in the Log4j 2 implementation classes but may leave the application susceptible to changes in Log4j 2 internals.</p> 
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           answered&nbsp; 
          <span title="2011-01-04 21:51:53Z" style="margin:0px; padding:0px; border:0px">Jan 4 '11 at 21:51</span> 
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            <td style="margin:0px; padding:0px; border:0px; font-size:13px"> <span title="number of 'useful comment' votes received" style="margin:0px; padding:0px 4px 0px 0px; border:0px; color:rgb(145,153,161)">3</span></td> 
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          <span style="margin:0px; padding:0px; border:0px">For only runtime dependencies&nbsp;<code style="margin:0px; padding:1px 5px; border:0px; font-family:Consolas,Menlo,Monaco,&quot;Lucida Console&quot;,&quot;Liberation Mono&quot;,&quot;DejaVu Sans Mono&quot;,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,monospace,sans-serif; background-color:rgb(239,240,241)">LogManager.getLogger(Class.forName("org.hibernate.util.JDBCE‌xceptionReporter")).‌setLevel(Level.FATAL‌);</code></span>&nbsp;–&nbsp; 
          <a href="http://stackoverflow.com/users/393046/celinhc" title="657 reputation" style="margin:0px; padding:0px; border:0px; color:rgb(0,119,204); text-decoration:none; white-space:nowrap" rel="nofollow">CelinHC</a>&nbsp; 
          <span style="margin:0px; padding:0px; border-top:0px; border-right:0px; border-bottom:none; border-left:0px; color:rgb(145,153,161)"><span title="2011-10-16 18:38:32Z" style="margin:0px; padding:0px; border:0px">Oct 16 '11 at 18:38</span></span> 
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            <td style="margin:0px; padding:0px; border:0px; font-size:13px"> <span title="number of 'useful comment' votes received" style="margin:0px; padding:0px 4px 0px 0px; border:0px; color:rgb(145,153,161)">2</span></td> 
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          <span style="margin:0px; padding:0px; border:0px">Note that the log4j 2 API does not provide a "setLevel" method.</span>&nbsp;–&nbsp; 
          <a href="http://stackoverflow.com/users/875449/chriscantrell" title="2,053 reputation" style="margin:0px; padding:0px; border:0px; color:rgb(0,119,204); text-decoration:none; white-space:nowrap" rel="nofollow">ChrisCantrell</a>&nbsp; 
          <span style="margin:0px; padding:0px; border-top:0px; border-right:0px; border-bottom:none; border-left:0px; color:rgb(145,153,161)"><span title="2013-10-29 20:36:12Z" style="margin:0px; padding:0px; border:0px">Oct 29 '13 at 20:36</span></span> 
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            <td style="margin:0px; padding:0px; border:0px; font-size:13px"> <span title="number of 'useful comment' votes received" style="margin:0px; padding:0px 4px 0px 0px; border:0px; color:rgb(145,153,161)">2</span></td> 
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          <span style="margin:0px; padding:0px; border:0px">But this only sets the root logger , isn't it? If individual levels are set for loggers under root, setting the root logger will have no effect on those LOGGER's. Wouldn't we have to do something like root.getLoggerRepository().getCurrentCategories(), iterate over each instance of the logger and set LEVELs for each logger? @AaronMcIver</span>&nbsp;–&nbsp; 
          <a href="http://stackoverflow.com/users/3185056/vishal-p" title="438 reputation" style="margin:0px; padding:0px; border:0px; color:rgb(0,119,204); text-decoration:none; white-space:nowrap" rel="nofollow">Vishal P</a>&nbsp; 
          <span style="margin:0px; padding:0px; border-top:0px; border-right:0px; border-bottom:none; border-left:0px; color:rgb(145,153,161)"><span title="2014-07-11 09:17:34Z" style="margin:0px; padding:0px; border:0px">Jul 11 '14 at 9:17</span></span> 
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          <span style="margin:0px; padding:0px; border:0px">@ChrisCantrell Log4j 2&nbsp;<a href="http://stackoverflow.com/questions/23434252/programmatically-change-log-level-in-log4j2" style="margin:0px; padding:0px; border:0px; color:rgb(0,89,153); text-decoration:none" rel="nofollow">does provide a way to do this</a>, although it's not as simple.</span>&nbsp;–&nbsp; 
          <a href="http://stackoverflow.com/users/1313268/coraythan" title="5,236 reputation" style="margin:0px; padding:0px; border:0px; color:rgb(0,119,204); text-decoration:none; white-space:nowrap" rel="nofollow">CorayThan</a>&nbsp; 
          <span style="margin:0px; padding:0px; border-top:0px; border-right:0px; border-bottom:none; border-left:0px; color:rgb(145,153,161)"><span title="2014-07-21 17:38:59Z" style="margin:0px; padding:0px; border:0px">Jul 21 '14 at 17:38</span></span> 
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            <td style="margin:0px; padding:0px; border:0px; font-size:13px"> <span title="number of 'useful comment' votes received" style="margin:0px; padding:0px 4px 0px 0px; border:0px; color:rgb(145,153,161)">1</span></td> 
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          <span style="margin:0px; padding:0px; border:0px">Log4j2 can be configured to refresh its configuration by scanning the log4j2.xml file (or equivalent) at given intervals. E.g. &lt;Configuration status="warn" monitorInterval="5" name="tryItApp" packages=""&gt;</span>&nbsp;–&nbsp; 
          <a href="http://stackoverflow.com/users/116810/kimball-robinson" title="1,994 reputation" style="margin:0px; padding:0px; border:0px; color:rgb(0,119,204); text-decoration:none; white-space:nowrap" rel="nofollow">Kimball Robinson</a>&nbsp; 
          <span style="margin:0px; padding:0px; border-top:0px; border-right:0px; border-bottom:none; border-left:0px; color:rgb(145,153,161)"><span title="2015-08-31 16:56:58Z" style="margin:0px; padding:0px; border:0px">Aug 31 '15 at 16:56</span></span> 
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     <h1 style="margin:0px 0px 1em; padding:0px; border:0px; font-size:21px; line-height:1.3; word-wrap:break-word"> File Watchdog</h1> 
     <p style="margin-top:0px; margin-bottom:1em; padding-top:0px; padding-bottom:0px; border:0px; clear:both"> Log4j is able to watch the&nbsp;<code style="margin:0px; padding:1px 5px; border:0px; font-size:13px; font-family:Consolas,Menlo,Monaco,&quot;Lucida Console&quot;,&quot;Liberation Mono&quot;,&quot;DejaVu Sans Mono&quot;,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,monospace,sans-serif; background-color:rgb(239,240,241); white-space:pre-wrap">log4j.xml</code>&nbsp;file for configuration changes. If you change the log4j file, log4j will automatically refresh the log levels according to your changes. See the documentation of&nbsp;<code style="margin:0px; padding:1px 5px; border:0px; font-size:13px; font-family:Consolas,Menlo,Monaco,&quot;Lucida Console&quot;,&quot;Liberation Mono&quot;,&quot;DejaVu Sans Mono&quot;,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,monospace,sans-serif; background-color:rgb(239,240,241); white-space:pre-wrap">org.apache.log4j.xml.DOMConfigurator.configureAndWatch(String,long</code>) for details. The default wait time between checks is 60 seconds. These changes would be persistent, since you directly change the configuration file on the filesystem. All you need to do is to invoke DOMConfigurator.configureAndWatch() once.</p> 
     <p style="margin-top:0px; margin-bottom:1em; padding-top:0px; padding-bottom:0px; border:0px; clear:both"> <span style="margin:0px; padding:0px; border:0px">Caution: configureAndWatch method is unsafe for use in J2EE environments due to a Thread leak</span></p> 
     <h1 style="margin:0px 0px 1em; padding:0px; border:0px; font-size:21px; line-height:1.3; word-wrap:break-word"> JMX</h1> 
     <p style="margin-top:0px; margin-bottom:1em; padding-top:0px; padding-bottom:0px; border:0px; clear:both"> Another way to set the log level (or reconfiguring in general) log4j is by using JMX. Log4j registers its loggers as JMX MBeans. Using the application servers MBeanServer consoles (or JDK's jconsole.exe) you can reconfigure each individual loggers. These changes are not persistent and would be reset to the config as set in the configuration file after you restart your application (server).</p> 
     <h1 style="margin:0px 0px 1em; padding:0px; border:0px; font-size:21px; line-height:1.3; word-wrap:break-word"> Self-Made</h1> 
     <p style="margin-top:0px; margin-bottom:1em; padding-top:0px; padding-bottom:0px; border:0px; clear:both"> As described by Aaron, you can set the log level programmatically. You can implement it in your application in the way you would like it to happen. For example, you could have a GUI where the user or admin changes the log level and then call the&nbsp;<code style="margin:0px; padding:1px 5px; border:0px; font-size:13px; font-family:Consolas,Menlo,Monaco,&quot;Lucida Console&quot;,&quot;Liberation Mono&quot;,&quot;DejaVu Sans Mono&quot;,&quot;Bitstream Vera Sans Mono&quot;,&quot;Courier New&quot;,monospace,sans-serif; background-color:rgb(239,240,241); white-space:pre-wrap">setLevel()</code>&nbsp;methods on the logger. Whether you persist the settings somewhere or not is up to you.</p> 
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          <a href="http://stackoverflow.com/posts/4599083/revisions" title="show all edits to this post" style="margin:0px; padding:0px; border:0px; color:rgb(0,119,204); text-decoration:none" rel="nofollow">edited&nbsp;<span title="2012-12-06 15:30:18Z" style="margin:0px; padding:0px; border:0px">Dec 6 '12 at 15:30</span></a> 
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           answered&nbsp; 
          <span title="2011-01-04 22:22:42Z" style="margin:0px; padding:0px; border:0px">Jan 4 '11 at 22:22</span> 
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   <td style="margin:0px; padding:0px 15px 0px 0px; border:0px; font-size:13px; vertical-align:top"> &nbsp;</td> 
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            <td style="margin:0px; padding:0px; border:0px; font-size:13px"> <span title="number of 'useful comment' votes received" style="margin:0px; padding:0px 4px 0px 0px; border:0px; color:rgb(155,118,79)">6</span></td> 
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         <div style="margin:0px; padding:0px; border:0px"> 
          <span style="margin:0px; padding:0px; border:0px">A word of caution regarding log4j watchdog approach: "Because the configureAndWatch launches a separate watchdog thread, and because there is no way to stop this thread in log4j 1.2, the configureAndWatch method is unsafe for use in J2EE envrironments where applications are recycled". Reference:&nbsp;<a href="http://logging.apache.org/log4j/1.2/faq.html#a3.6" style="margin:0px; padding:0px; border:0px; color:rgb(0,89,153); text-decoration:none" rel="nofollow">Log4J FAQ</a></span>&nbsp;–&nbsp; 
          <a href="http://stackoverflow.com/users/389489/somu" title="1,137 reputation" style="margin:0px; padding:0px; border:0px; color:rgb(0,119,204); text-decoration:none; white-space:nowrap" rel="nofollow">Somu</a>&nbsp; 
          <span style="margin:0px; padding:0px; border-top:0px; border-right:0px; border-bottom:none; border-left:0px; color:rgb(145,153,161)"><span title="2011-11-29 19:29:08Z" style="margin:0px; padding:0px; border:0px">Nov 29 '11 at 19:29</span></span> 
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          <span style="margin:0px; padding:0px; border:0px">If i was to use configureAndWatch functionality of Log4j I could stop that watchdog thread in an EJB's @PostDestroy method (that's a good enough indicator of when the container is shutting down) That's it ? Or is there more to it that I am missing..!</span>&nbsp;–&nbsp; 
          <a href="http://stackoverflow.com/users/278938/robin-bajaj" title="450 reputation" style="margin:0px; padding:0px; border:0px; color:rgb(0,119,204); text-decoration:none; white-space:nowrap" rel="nofollow">robin bajaj</a>&nbsp; 
          <span style="margin:0px; padding:0px; border-top:0px; border-right:0px; border-bottom:none; border-left:0px; color:rgb(145,153,161)"><span title="2013-09-27 20:08:48Z" style="margin:0px; padding:0px; border:0px">Sep 27 '13 at 20:08</span></span>&nbsp; 
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          <span style="margin:0px; padding:0px; border:0px">sorry I meant @PreDestroy method</span>&nbsp;–&nbsp; 
          <a href="http://stackoverflow.com/users/278938/robin-bajaj" title="450 reputation" style="margin:0px; padding:0px; border:0px; color:rgb(0,119,204); text-decoration:none; white-space:nowrap" rel="nofollow">robin bajaj</a>&nbsp; 
          <span style="margin:0px; padding:0px; border-top:0px; border-right:0px; border-bottom:none; border-left:0px; color:rgb(145,153,161)"><span title="2013-09-27 20:14:20Z" style="margin:0px; padding:0px; border:0px">Sep 27 '13 at 20:14</span></span>&nbsp; 
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          <span style="margin:0px; padding:0px; border:0px">"<span style="margin:0px; padding:0px; border:0px">Log4j registers its loggers as JMX MBeans.</span>". My servlet uses log4j 1.2 I don't see any log4j MBeans.</span>&nbsp;–&nbsp; 
          <a href="http://stackoverflow.com/users/923560/abdull" title="6,643 reputation" style="margin:0px; padding:0px; border:0px; color:rgb(0,119,204); text-decoration:none; white-space:nowrap" rel="nofollow">Abdull</a>&nbsp; 
          <span style="margin:0px; padding:0px; border-top:0px; border-right:0px; border-bottom:none; border-left:0px; color:rgb(145,153,161)"><span title="2016-01-18 13:39:38Z" style="margin:0px; padding:0px; border:0px">Jan 18 at 13:39</span></span> 
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          <span style="margin:0px; padding:0px; border:0px"><span style="margin:0px; padding:0px; border:0px">All you need to do is to invoke DOMConfigurator.configureAndWatch() once.</span>&nbsp;How can I achieve this ?</span>&nbsp;–&nbsp; 
          <a href="http://stackoverflow.com/users/2674303/gstackoverflow" title="6,281 reputation" style="margin:0px; padding:0px; border:0px; color:rgb(0,119,204); text-decoration:none; white-space:nowrap" rel="nofollow">gstackoverflow</a>&nbsp; 
          <span style="margin:0px; padding:0px; border-top:0px; border-right:0px; border-bottom:none; border-left:0px; color:rgb(145,153,161)"><span title="2016-09-05 10:22:00Z" style="margin:0px; padding:0px; border:0px">Sep 5 at 10:22</span></span> 
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     <a title="Use comments to ask for more information or suggest improvements. Avoid comments like “+1” or “thanks”." style="margin:0px; padding:0px 3px 2px; border:0px; color:rgb(132,141,149)" rel="nofollow">add a comment</a> 
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&lt;Appenders&gt;
        &lt;RollingFile name="MY_TRY_IT"
                     fileName="/var/log/tryIt.log"
                     filePattern="/var/log/tryIt-%i.log.gz"&gt;
            &lt;Policies&gt;
                &lt;SizeBasedTriggeringPolicy size="25 MB"/&gt;
            &lt;/Policies&gt;
            ...
        &lt;/RollingFile&gt;
    &lt;/Appenders&gt;

&lt;Loggers&gt;
        &lt;Root level="error"&gt;
            &lt;AppenderRef ref="MY_TRY_IT"/&gt;
        &lt;/Root&gt;
    &lt;/Loggers&gt;

&lt;/Configuration&gt;
</code></pre> 
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         <div style="margin:1px 0px 4px; padding:0px; border:0px; font-size:12px; white-space:nowrap">
           answered&nbsp; 
          <span title="2015-08-31 16:58:14Z" style="margin:0px; padding:0px; border:0px">Aug 31 '15 at 16:58</span> 
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          </div> 
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         <div style="margin:0px 0px 0px 8px; padding:0px; border:0px; line-height:17px; word-wrap:break-word; float:left"> 
          <a href="http://stackoverflow.com/users/116810/kimball-robinson" style="margin:0px; padding:0px; border:0px; color:rgb(0,119,204); text-decoration:none" rel="nofollow">Kimball Robinson</a> 
          <div style="margin:0px; padding:0px; border:0px"> 
           <span title="reputation score " style="margin:0px 2px 0px 0px; padding:0px; border:0px; font-size:12px; font-weight:bold">1,994</span> 
           <span title="5 gold badges" style="margin:0px 3px 0px 2px; padding:0px; border:0px"><span style="margin:0px 3px 0px 2px; padding:0px; border:0px; display:inline-block; overflow:hidden; line-height:inherit; vertical-align:text-bottom; width:6px; height:14px"></span><span style="margin:0px; padding:0px; border:0px; font-size:12px">5</span></span> 
           <span title="27 silver badges" style="margin:0px 3px 0px 2px; padding:0px; border:0px"><span style="margin:0px 3px 0px 2px; padding:0px; border:0px; display:inline-block; overflow:hidden; line-height:inherit; vertical-align:text-bottom; width:6px; height:14px"></span><span style="margin:0px; padding:0px; border:0px; font-size:12px">27</span></span> 
           <span title="46 bronze badges" style="margin:0px 3px 0px 2px; padding:0px; border:0px"><span style="margin:0px 3px 0px 2px; padding:0px; border:0px; display:inline-block; overflow:hidden; line-height:inherit; vertical-align:text-bottom; width:6px; height:14px"></span><span style="margin:0px; padding:0px; border:0px; font-size:12px">46</span></span> 
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  <tr style="margin:0px; padding:0px; border:0px"> 
   <td style="margin:0px; padding:0px 15px 0px 0px; border:0px; font-size:13px; vertical-align:top"> &nbsp;</td> 
   <td style="margin:0px; padding:0px; border:0px; font-size:13px"> 
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     <table style="margin:0px; padding:0px; border:0px; font-size:13px; border-spacing:0px; border-collapse:collapse; width:660px"> 
      <tbody style="margin:0px; padding:0px; border:0px"> 
       <tr style="margin:0px; padding:0px; border:0px"> 
        <td style="margin:0px; padding:6px 6px 6px 0px; border-width:0px 0px 1px; border-top-style:initial; border-right-style:initial; border-bottom-style:solid; border-left-style:initial; border-top-color:initial; border-right-color:initial; border-bottom-color:rgb(239,240,241); border-left-color:initial; font-size:13px; vertical-align:top; line-height:1.3"> 
         <table style="margin:0px; padding:0px; border:0px; font-size:13px; border-spacing:0px; border-collapse:collapse"> 
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            <td style="margin:0px; padding:0px; border:0px; font-size:13px"> </td> 
            <td style="margin:0px; padding:0px; border:0px; font-size:13px">&nbsp;</td> 
           </tr> 
          </tbody> 
         </table> </td> 
        <td style="margin:0px; padding:6px 6px 6px 0px; border-width:0px 0px 1px; border-top-style:initial; border-right-style:initial; border-bottom-style:solid; border-left-style:initial; border-top-color:initial; border-right-color:initial; border-bottom-color:rgb(239,240,241); border-left-color:initial; font-size:13px; vertical-align:top; line-height:1.3"> 
         <div style="margin:0px; padding:0px; border:0px"> 
          <span style="margin:0px; padding:0px; border:0px">Does not seem to work in log4j2</span>&nbsp;–&nbsp; 
          <a href="http://stackoverflow.com/users/156522/vsingh" title="2,037 reputation" style="margin:0px; padding:0px; border:0px; color:rgb(0,119,204); text-decoration:none; white-space:nowrap" rel="nofollow">vsingh</a>&nbsp; 
          <span style="margin:0px; padding:0px; border-top:0px; border-right:0px; border-bottom:none; border-left:0px; color:rgb(145,153,161)"><span title="2016-03-03 18:53:29Z" style="margin:0px; padding:0px; border:0px">Mar 3 at 18:53</span></span> 
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     <a title="Use comments to ask for more information or suggest improvements. Avoid comments like “+1” or “thanks”." style="margin:0px; padding:0px 3px 2px; border:0px; color:rgb(132,141,149)" rel="nofollow">add a comment</a> 
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if (Log4jReconfigurator.class.getResource("/" + name) != null) {
      String logConfigPath = Log4jReconfigurator.class.getResource("/" + name).getPath();
      logger.warn("Using log4j configuration: " + logConfigPath);
      try (InputStream defaultIs = Log4jReconfigurator.class.getResourceAsStream("/" + name)) {
        new DOMConfigurator().doConfigure(defaultIs, LogManager.getLoggerRepository());
      } catch (IOException e) {
        logger.error("Failed to reconfigure log4j configuration, could not find file " + logConfigPath + " on the classpath", e);
      } catch (FactoryConfigurationError e) {
        logger.error("Failed to reconfigure log4j configuration, could not load file " + logConfigPath, e);
      }
    } else {
      logger.error("Could not find log4j configuration file " + name + ".xml on classpath");
    }
  }
</code></pre> 
     <p style="margin-top:0px; margin-bottom:1em; padding-top:0px; padding-bottom:0px; border:0px; clear:both"> Just call this with the appropriate config name, and make sure that you put the templates on the classpath.</p> 
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       <td style="margin:0px; padding:0px; border:0px; font-size:13px; vertical-align:top"> 
        <div style="margin:0px; padding:2px 0px 0px; border:0px"> 
         <a href="http://stackoverflow.com/a/35083184" title="short permalink to this answer" style="margin:0px; padding:0px 3px 2px; border:0px; color:rgb(132,141,149); text-decoration:none; display:inline-block" rel="nofollow">share</a> 
         <span style="margin:0px; padding:0px; border:0px; font-size:1px; color:rgb(27,64,114); visibility:hidden; display:inline-block"></span> 
         <a href="http://stackoverflow.com/posts/35083184/edit" title="" style="margin:0px; padding:0px 3px 2px; border:0px; color:rgb(132,141,149); text-decoration:none; display:inline-block" rel="nofollow">improve this answer</a> 
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       <td align="right" style="margin:0px; padding:0px; border:0px; font-size:13px; vertical-align:top; width:200px"> 
        <div style="margin:0px; padding:5px 6px 7px 7px; border:0px; width:200px; color:rgb(106,115,124)"> 
         <div style="margin:1px 0px 4px; padding:0px; border:0px; font-size:12px; white-space:nowrap">
           answered&nbsp; 
          <span title="2016-01-29 11:17:16Z" style="margin:0px; padding:0px; border:0px">Jan 29 at 11:17</span> 
         </div> 
         <div style="margin:0px; padding:0px; border:0px; float:left; width:32px; height:32px"> 
          <a href="http://stackoverflow.com/users/4452578/ian-sparkes" style="margin:0px; padding:0px; border:0px; color:rgb(0,119,204); text-decoration:none" rel="nofollow"></a> 
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           <img src="https://lh4.googleusercontent.com/-2lZPCMwlbeY/AAAAAAAAAAI/AAAAAAAAAAA/7huvVCISupc/photo.jpg?sz=32" alt="" width="32" height="32" style="margin:0px auto; padding:0px; border:0px; width:32px; height:32px"> 
          </div> 
         </div> 
         <div style="margin:0px 0px 0px 8px; padding:0px; border:0px; line-height:17px; word-wrap:break-word; float:left"> 
          <a href="http://stackoverflow.com/users/4452578/ian-sparkes" style="margin:0px; padding:0px; border:0px; color:rgb(0,119,204); text-decoration:none" rel="nofollow">Ian Sparkes</a> 
          <div style="margin:0px; padding:0px; border:0px"> 
           <span title="reputation score " style="margin:0px 2px 0px 0px; padding:0px; border:0px; font-size:12px; font-weight:bold">356</span> 
           <span title="2 silver badges" style="margin:0px 3px 0px 2px; padding:0px; border:0px"><span style="margin:0px 3px 0px 2px; padding:0px; border:0px; display:inline-block; overflow:hidden; line-height:inherit; vertical-align:text-bottom; width:6px; height:14px"></span><span style="margin:0px; padding:0px; border:0px; font-size:12px">2</span></span> 
           <span title="7 bronze badges" style="margin:0px 3px 0px 2px; padding:0px; border:0px"><span style="margin:0px 3px 0px 2px; padding:0px; border:0px; display:inline-block; overflow:hidden; line-height:inherit; vertical-align:text-bottom; width:6px; height:14px"></span><span style="margin:0px; padding:0px; border:0px; font-size:12px">7</span></span> 
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  <tr style="margin:0px; padding:0px; border:0px"> 
   <td style="margin:0px; padding:0px 15px 0px 0px; border:0px; font-size:13px; vertical-align:top"> &nbsp;</td> 
   <td style="margin:0px; padding:0px; border:0px; font-size:13px"> 
    <div style=""> 
     <table style="margin:0px; padding:0px; border:0px; font-size:13px; border-spacing:0px; border-collapse:collapse; width:660px"> 
      <tbody style="margin:0px; padding:0px; border:0px"> 
       <tr style="margin:0px; padding:0px; border:0px"> 
        <td style="margin:0px; padding:6px 6px 6px 0px; border-width:0px 0px 1px; border-top-style:initial; border-right-style:initial; border-bottom-style:solid; border-left-style:initial; border-top-color:initial; border-right-color:initial; border-bottom-color:rgb(239,240,241); border-left-color:initial; font-size:13px; vertical-align:top; line-height:1.3"> 
         <table style="margin:0px; padding:0px; border:0px; font-size:13px; border-spacing:0px; border-collapse:collapse"> 
          <tbody style="margin:0px; padding:0px; border:0px"> 
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            <td style="margin:0px; padding:0px; border:0px; font-size:13px"> </td> 
            <td style="margin:0px; padding:0px; border:0px; font-size:13px">&nbsp;</td> 
           </tr> 
          </tbody> 
         </table> </td> 
        <td style="margin:0px; padding:6px 6px 6px 0px; border-width:0px 0px 1px; border-top-style:initial; border-right-style:initial; border-bottom-style:solid; border-left-style:initial; border-top-color:initial; border-right-color:initial; border-bottom-color:rgb(239,240,241); border-left-color:initial; font-size:13px; vertical-align:top; line-height:1.3"> 
         <div style="margin:0px; padding:0px; border:0px"> 
          <span style="margin:0px; padding:0px; border:0px">what is the triggering point of this method? how does it know this method has to be invoked whenever there's a change in the log4j config?</span>&nbsp;–&nbsp; 
          <a href="http://stackoverflow.com/users/282345/asgs" title="2,718 reputation" style="margin:0px; padding:0px; border:0px; color:rgb(0,119,204); text-decoration:none; white-space:nowrap" rel="nofollow">asgs</a>&nbsp; 
          <span style="margin:0px; padding:0px; border-top:0px; border-right:0px; border-bottom:none; border-left:0px; color:rgb(145,153,161)"><span title="2016-03-31 20:24:12Z" style="margin:0px; padding:0px; border:0px">Mar 31 at 20:24</span></span> 
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        <td style="margin:0px; padding:6px 6px 6px 0px; border-width:0px 0px 1px; border-top-style:initial; border-right-style:initial; border-bottom-style:solid; border-left-style:initial; border-top-color:initial; border-right-color:initial; border-bottom-color:rgb(239,240,241); border-left-color:initial; font-size:13px; vertical-align:top; line-height:1.3"> 
         <table style="margin:0px; padding:0px; border:0px; font-size:13px; border-spacing:0px; border-collapse:collapse"> 
          <tbody style="margin:0px; padding:0px; border:0px"> 
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            <td style="margin:0px; padding:0px; border:0px; font-size:13px"> </td> 
            <td style="margin:0px; padding:0px; border:0px; font-size:13px">&nbsp;</td> 
           </tr> 
          </tbody> 
         </table> </td> 
        <td style="margin:0px; padding:6px 6px 6px 0px; border-width:0px 0px 1px; border-top-style:initial; border-right-style:initial; border-bottom-style:solid; border-left-style:initial; border-top-color:initial; border-right-color:initial; border-bottom-color:rgb(239,240,241); border-left-color:initial; font-size:13px; vertical-align:top; line-height:1.3"> 
         <div style="margin:0px; padding:0px; border:0px"> 
          <span style="margin:0px; padding:0px; border:0px">No, it is on demand.</span>&nbsp;–&nbsp; 
          <a href="http://stackoverflow.com/users/4452578/ian-sparkes" title="356 reputation" style="margin:0px; padding:0px; border:0px; color:rgb(0,119,204); text-decoration:none; white-space:nowrap" rel="nofollow">Ian Sparkes</a>&nbsp; 
          <span style="margin:0px; padding:0px; border-top:0px; border-right:0px; border-bottom:none; border-left:0px; color:rgb(145,153,161)"><span title="2016-04-01 20:45:55Z" style="margin:0px; padding:0px; border:0px">Apr 1 at 20:45</span></span> 
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        <td style="margin:0px; padding:6px 6px 6px 0px; border-width:0px 0px 1px; border-top-style:initial; border-right-style:initial; border-bottom-style:solid; border-left-style:initial; border-top-color:initial; border-right-color:initial; border-bottom-color:rgb(239,240,241); border-left-color:initial; font-size:13px; vertical-align:top; line-height:1.3"> 
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            <td style="margin:0px; padding:0px; border:0px; font-size:13px"> </td> 
            <td style="margin:0px; padding:0px; border:0px; font-size:13px">&nbsp;</td> 
           </tr> 
          </tbody> 
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        <td style="margin:0px; padding:6px 6px 6px 0px; border-width:0px 0px 1px; border-top-style:initial; border-right-style:initial; border-bottom-style:solid; border-left-style:initial; border-top-color:initial; border-right-color:initial; border-bottom-color:rgb(239,240,241); border-left-color:initial; font-size:13px; vertical-align:top; line-height:1.3"> 
         <div style="margin:0px; padding:0px; border:0px"> 
          <span style="margin:0px; padding:0px; border:0px">I still don't get what you mean "on demand". Can you please show a snippet where you hook this method up?</span>–&nbsp; 
          <a href="http://stackoverflow.com/users/282345/asgs" title="2,718 reputation" style="margin:0px; padding:0px; border:0px; color:rgb(0,119,204); text-decoration:none; white-space:nowrap" rel="nofollow">asgs</a>&nbsp; 
          <span style="margin:0px; padding:0px; border-top:0px; border-right:0px; border-bottom:none; border-left:0px; color:rgb(145,153,161)"><span title="2016-04-02 05:42:41Z" style="margin:0px; padding:0px; border:0px">Apr 2 at 5:42</span></span> 
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        <td style="margin:0px; padding:6px 6px 6px 0px; border-width:0px 0px 1px; border-top-style:initial; border-right-style:initial; border-bottom-style:solid; border-left-style:initial; border-top-color:initial; border-right-color:initial; border-bottom-color:rgb(239,240,241); border-left-color:initial; font-size:13px; width:15px; vertical-align:top; line-height:1.3"> 
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            <td style="margin:0px; padding:0px; border:0px; font-size:13px"> <span title="number of 'useful comment' votes received" style="margin:0px; padding:0px 4px 0px 0px; border:0px; color:rgb(145,153,161)">1</span></td> 
            <td style="margin:0px; padding:0px; border:0px; font-size:13px">&nbsp;</td> 
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        <td style="margin:0px; padding:6px 6px 6px 0px; border-width:0px 0px 1px; border-top-style:initial; border-right-style:initial; border-bottom-style:solid; border-left-style:initial; border-top-color:initial; border-right-color:initial; border-bottom-color:rgb(239,240,241); border-left-color:initial; font-size:13px; vertical-align:top; line-height:1.3"> 
         <div style="margin:0px; padding:0px; border:0px"> 
          <span style="margin:0px; padding:0px; border:0px">Here you go: This is a snippet from the Controller where we use it. We have an admin page with some links to dynamically reconfigure logging, which then makes a GET to the link&nbsp;<span style="margin:0px; padding:0px; border:0px">/admin/setLogLevel?level=Error</span>&nbsp;and then we catch this in the controller like this&nbsp;<span style="margin:0px; padding:0px; border:0px">@RequestMapping(value = "setLogLevel", method = RequestMethod.GET) public ModelAndView setLogLevel(@RequestParam(value = "level", required = true) String level) { Log4jReconfigurator.reconfigureExisting(level);</span></span>&nbsp;–&nbsp; 
          <a href="http://stackoverflow.com/users/4452578/ian-sparkes" title="356 reputation" style="margin:0px; padding:0px; border:0px; color:rgb(0,119,204); text-decoration:none; white-space:nowrap" rel="nofollow">Ian Sparkes</a>&nbsp; 
          <span style="margin:0px; padding:0px; border-top:0px; border-right:0px; border-bottom:none; border-left:0px; color:rgb(145,153,161)"><span title="2016-04-05 09:49:42Z" style="margin:0px; padding:0px; border:0px">Apr 5 at 9:49</span></span>&nbsp; 
          <span title="this comment was edited 2 times" style="margin:0px; padding:0px; border:0px; overflow:hidden; display:inline-block; vertical-align:text-bottom; line-height:12px; height:15px; width:16px"></span> 
         </div> </td> 
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        <td style="margin:0px; padding:6px 6px 6px 0px; border-width:0px 0px 1px; border-top-style:initial; border-right-style:initial; border-bottom-style:solid; border-left-style:initial; border-top-color:initial; border-right-color:initial; border-bottom-color:rgb(239,240,241); border-left-color:initial; font-size:13px; vertical-align:top; line-height:1.3"> 
         <table style="margin:0px; padding:0px; border:0px; font-size:13px; border-spacing:0px; border-collapse:collapse"> 
          <tbody style="margin:0px; padding:0px; border:0px"> 
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            <td style="margin:0px; padding:0px; border:0px; font-size:13px"> </td> 
            <td style="margin:0px; padding:0px; border:0px; font-size:13px">&nbsp;</td> 
           </tr> 
          </tbody> 
         </table> </td> 
        <td style="margin:0px; padding:6px 6px 6px 0px; border-width:0px 0px 1px; border-top-style:initial; border-right-style:initial; border-bottom-style:solid; border-left-style:initial; border-top-color:initial; border-right-color:initial; border-bottom-color:rgb(239,240,241); border-left-color:initial; font-size:13px; vertical-align:top; line-height:1.3"> 
         <div style="margin:0px; padding:0px; border:0px"> 
          <span style="margin:0px; padding:0px; border:0px">So, "on demand" means "when the user clicks the button" in my case</span>&nbsp;–&nbsp; 
          <a href="http://stackoverflow.com/users/4452578/ian-sparkes" title="356 reputation" style="margin:0px; padding:0px; border:0px; color:rgb(0,119,204); text-decoration:none; white-space:nowrap" rel="nofollow">Ian Sparkes</a>&nbsp; 
          <span style="margin:0px; padding:0px; border-top:0px; border-right:0px; border-bottom:none; border-left:0px; color:rgb(145,153,161)"><span title="2016-04-05 09:55:18Z" style="margin:0px; padding:0px; border:0px">Apr 5 at 9:55</span></span> 
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    <div style="margin:0px; padding:0px; border:0px"> 
     <a title="expand to show all comments on this post" href="http://stackoverflow.com/questions/4598702/dynamically-changing-log4j-log-level#" style="margin:0px; padding:0px 3px 2px; border:0px; color:rgb(0,119,204); text-decoration:none" rel="nofollow">show&nbsp;<span style="margin:0px; padding:0px; border:0px">2</span>&nbsp;more comments</a> 
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&lt;dependency&gt;
    &lt;groupId&gt;log4j&lt;/groupId&gt;
    &lt;artifactId&gt;apache-log4j-extras&lt;/artifactId&gt;
    &lt;version&gt;1.2.17&lt;/version&gt;
&lt;/dependency&gt;
</code></pre> 
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           answered&nbsp; 
          <span title="2016-05-05 17:16:27Z" style="margin:0px; padding:0px; border:0px">May 5 at 17:16</span> 
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          <span style="margin:0px; padding:0px; border:0px">Whatever you mentioned seems to be fine, but the question is about dynamically changing the logging level.</span>–&nbsp; 
          <a href="http://stackoverflow.com/users/2452417/azim" title="682 reputation" style="margin:0px; padding:0px; border:0px; color:rgb(0,119,204); text-decoration:none; white-space:nowrap" rel="nofollow">Azim</a>&nbsp; 
          <span style="margin:0px; padding:0px; border-top:0px; border-right:0px; border-bottom:none; border-left:0px; color:rgb(145,153,161)"><span title="2016-07-13 12:11:27Z" style="margin:0px; padding:0px; border:0px">Jul 13 at 12:11</span></span> 
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