动态改变log4j的级别(level)

Changing the log level is simple; modifying other portions of the configuration will pose a more in depth approach.

RootLogger().setLevel(Level.DEBUG);

The changes are permanent through the life cyle of the Logger. On reinitialization the configuration will be read and used as setting the level at runtime does not persist the level change.

UPDATE: If you are using Log4j 2 you should remove the calls to setLevel per the documentationas this can be achieved via implementation classes.

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.

File Watchdog

Log4j is able to watch the l 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 org.figureAndWatch(String,long) 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 figureAndWatch() once.

Caution: configureAndWatch method is unsafe for use in J2EE environments due to a Thread leak

JMX

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') 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).

Self-Made

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 setLevel() methods on the logger. Whether you persist the settings somewhere or not is up to you.

Log4j2 can be configured to refresh its configuration by scanning l file (or equivalent) at given intervals. Just add the "monitorInterval" parameter to your configuration tag. See line 2 of the l file, which tells log4j to to re-scan its configuration if more than 5 seconds have passed since the last log event.

<?xml version="1.0" encoding="UTF-8" ?>
<Configuration status="warn" monitorInterval="5" name="tryItApp" packages=""><Appenders><RollingFile name="MY_TRY_IT"fileName="/var/log/tryIt.log"filePattern="/var/log/tryIt-%"><Policies><SizeBasedTriggeringPolicy size="25 MB"/></Policies>...</RollingFile></Appenders><Loggers><Root level="error"><AppenderRef ref="MY_TRY_IT"/></Root></Loggers></Configuration>

With log4j 1.x I find the best way is to use a DOMConfigurator to submit one of a predefined set of XML log configurations (say, one for normal use and one for debugging).

Making use of these can be done with something like this:

  public static void reconfigurePredefined(String newLoggerConfigName) {String name = LowerCase();if ("default".equals(name)) {name = &#l";} else {name = "log4j-" + name + ".xml";}if (Resource("/" + name) != null) {String logConfigPath = Resource("/" + name).getPath();logger.warn("Using log4j configuration: " + logConfigPath);try (InputStream defaultIs = ResourceAsStream("/" + name)) {new DOMConfigurator().doConfigure(defaultIs, LoggerRepository());} catch (IOException e) {("Failed to reconfigure log4j configuration, could not find file " + logConfigPath + " on the classpath", e);} catch (FactoryConfigurationError e) {("Failed to reconfigure log4j configuration, could not load file " + logConfigPath, e);}} else {("Could not find log4j configuration file " + name + ".xml on classpath");}}

Just call this with the appropriate config name, and make sure that you put the templates on the classpath.

I did this to dynamically Change log4j log level and it worked for me, I have n't referred any document. I used this system property value to set my logfile name. I used the same technique to set logging level as well, and it worked

passed this as JVM parameter (I use Java 1.7)

java -Dlogging.level=DEBUG -cp xxxxxx.jar  xxxxx.java

in the log4j.properties file, I added this entry

Logger=${logging.level},file,stdout

I tried

 java -Dlogging.level=DEBUG -cp xxxxxx.jar  xxxxx.javajava -Dlogging.level=INFO-cp xxxxxx.jar  xxxxx.javajava -Dlogging.level=OFF -cp xxxxxx.jar  xxxxx.java

It all worked. hope this helps!

I have these following dependencies in l

<dependency><groupId>log4j</groupId><artifactId>log4j</artifactId><version>1.2.17</version>
</dependency><dependency><groupId>log4j</groupId><artifactId>apache-log4j-extras</artifactId><version>1.2.17</version>
</dependency>