The way log4j 1 worked and how log4j 2 works are a bit different. Log4j 1 only 
had Loggers. When you wanted to configure a Logger you obtained a Logger and 
added an appender to it or set its logging level. If you created a Logger that 
didn’t have a logging level it would go to its parent Logger and get it from 
there. So setting a Logger’s logging level to null basically said “look at your 
parent”.  When an application wants to log something it also obtains a Logger. 
So the Loggers used for logging and configuration were the same. In order to 
reconfigure, Log4j 1 would clear everything from the Loggers and then start 
adding configuration back to them as it processed the configuration. During the 
time that the Loggers are cleared and before configuration is added back events 
are ignored.

Log4j 2 doesn’t work this way at all. When the configuration is read a set of 
LoggerConfig objects is created. These all contain the same information that is 
in the configuration file. When an application wants to log it gets a Logger. 
The Logger looks for a LoggerConfig with its name or, if one isn’t found, one 
of its ancestors. The Logger then is set with a reference to the LoggerConfig 
that provides its configuration and it copies that LoggerConfig’s logging level 
into it to improve performance. Thus, when you want to  change a logging level 
you need to locate the LoggerConfig for the Logger, update its logging level, 
and then call updateLoggers to cause all Loggers to reevaluate which 
LoggerConfig they should be using and what their current logging level is.

There are several ways to deal with changes. 
You add a listener to handle configuration changes. This would allow you to 
reinsert changes to the configuration.
You can create your own Configuration and combine it with the user’s 
configuration using a CompositeConfiguration. Your configuration can be created 
with a config file or via the ConfigurationBuilder.
You can extend XMLConfiguration and/or PropertiesConfiguration and add your own 
definitions to it.

I am sure there are other ways this can all be done depending on what you are 
trying to achieve. If you modify the logging level of a LoggerConfig and then a 
reconfigure occurs Log4j will automatically handle resetting the configuration. 
You don’t have to do anything. If you want to reinsert changes to the user’s 
configuration then you have to use one of the techniques I noted above.


> On Dec 17, 2017, at 3:40 PM, Paladox <> 
> wrote:
> "You didn’t answer what logging level you are setting to null and why."
> Im not really sure why it was set to null as this was done long before i 
> started contributing to gerrit.
> I can presume it was done because PropertyConfiguator would reload the file 
> but wouldn't discard anything else so if we set loggers through java then 
> reloading the file would not affect them. So i guess they wanted to make sure 
> everything goes back to the way it was.
> More explementation, because we have a ssh command that can set log levels 
> for either all or specific loggers we want to be able to remove the levels to 
> put it back to how it was done when the application was started. So ie if we 
> set debug on then that will be added to the loggers as
> but when the application was started that was not in the loggers so we did 
> not get any debug in the output.
> But we want to set it to the default by removing as loggers in 
> have different levels. IE in the file we have
> which is set to WARN
> but now because we did @ debug 
> will be debug and everything else 
> under class path that uses loggers.
> But users would not know every logger under so they wouldn't be 
> able to put them all back to the default so we set the log level to null and 
> reloaded the file without loosing any java appenders. But with log4j2 it 
> seems to restart as new.
>    On Sunday, 17 December 2017, 22:25:28 GMT, Ralph Goers 
> <> wrote:  
> You didn’t answer what logging level you are setting to null and why.
> I’m still not getting a clear picture of what the real requirements are. "we 
> use java to add appenders and other things because we want users to customise 
> the behavour through a config” tells me you want users to be able to use 
> their own configuration but not why you want to add appenders and “other 
> things” or what requirement you are trying to solve with them. What I need 
> here is some sort of “user story definition” like - “As a user of Gerrit I 
> need to be able to provide my own logging configuration while Gerrit makes 
> sure that error conditions are always logged even if my configuration doesn’t 
> specify it” or something like that. We can tell you how to implement 
> something once we understand what you are really trying to achieve. You 
> probably have done this before, but in case you haven’t done that before you 
> can look at 
> <>. Also, you might 
> have a definition of what you want the experience for a user of Gerrit to be 
> vs that of a developer. If so, tell me what they both are.
> Ralph
>> On Dec 17, 2017, at 1:58 PM, Paladox <> wrote:
>> for "“Then loads the property file” - what property file? The log4j 2 
>> configuration file?  Why would you set the log sell to null before reloaded 
>> the configuration? "
>> We doin't, we would load it after we set the log level to null.
>> Also for the "what". Well we use java to add appenders and other things 
>> because we want users to customise the behavour through a config. For 
>> example some users want log4j to log with json instead of the pattern 
>> layout. Though if users want to modify it more then a config they use the 
>> system property to override the default log4j configuation file and use 
>> there own.
>> On Sunday, 17 December 2017, 20:44:09 GMT, Ralph Goers 
>> <> wrote:
>> "Sets the log level to null” - which log level? The root, a particular 
>> logger, or a Threshold Filter on a particular appender? FWIW, in Log4j 1 
>> setting the log level to null on a Logger just means it will inherit from 
>> its parent. That is not necessarily the case in Log4j 2.
>> “Then loads the property file” - what property file? The log4j 2 
>> configuration file?  Why would you set the log sell to null before reloaded 
>> the configuration? 
>> “Without losing any appenders created with Java” - How are the appenders 
>> created with Java and why are they created with Java? You could use a 
>> composite configuration that adds your the “standard” configuration to what 
>> a user provides or you could extend XMLConfiguratoin with your own extra 
>> configuration.
>> In short, you still haven’t described what you want the resultant behavior 
>> to be. You are still describing “How?” instead of “What?”.  In other words - 
>> something like - “We want to require that a specific logger is always logged 
>> at error and those logs are always routed to a file named xxxx, regardless 
>> of what other things the user might configure”. 
>> Ralph
>>> On Dec 17, 2017, at 11:22 AM, Paladox < 
>>> <>> wrote:
>>> Im trying to migrate gerrit from log4j1 to log4j2.
>>> With this we have a ssh command that resets log levels (ie sets the log 
>>> level to null then loads the Property file without restarting from fresh 
>>> and loosing any appenders that were created with java).
>>>     On Sunday, 17 December 2017, 17:56:42 GMT, Ralph Goers 
>>> < <>> wrote:  
>>> Why are you trying to do this? What problem are you trying to solve? Simply 
>>> trying to port code from Log4j 1 to Log4j 2 without evaluating what the 
>>> best way is to achieve the desired results is not an approach I recommend.
>>> Ralph 
>>>> On Dec 16, 2017, at 1:18 PM, Paladox < 
>>>> <>> wrote:
>>>> Would like to add more to this question.
>>>> Im wondering is it possible to also reset log levels?
>>>> In log4j1.x we did
>>>>   private static void reset() throws MalformedURLException {    for 
>>>> (Enumeration<Logger> logger = LogManager.getCurrentLoggers(); 
>>>> logger.hasMoreElements(); ) {      logger.nextElement().setLevel(null);    
>>>> }
>>>>     String path = System.getProperty(JAVA_OPTIONS_LOG_CONFIG);    if 
>>>> (Strings.isNullOrEmpty(path)) {      
>>>> PropertyConfigurator.configure(Loader.getResource(LOG_CONFIGURATION));    
>>>> } else {      PropertyConfigurator.configure(new URL(path));    }  }
>>>> in log4j2 i carn't find any good replacements. Setting setLevel results in 
>>>> null pointer same would be for setAllLevels. (Works in log4j1).
>>>> Then when i try to reload the properties file it just resets everything 
>>>> then loads the file. Thus if you used some java code it would be lost and 
>>>> you would have to restart your java application to get the appenders or 
>>>> anything added with java code.
>>>> In log4j1 you need PropertyConfigurator.configure which re added the log 
>>>> levels that were from the file without resetting anything.
>>>>   On Friday, 15 December 2017, 16:50:28 GMT, Paladox 
>>>> < 
>>>> <>> wrote:  
>>>> Hi, im wondering if i could have some help with migrating from log4j1 to 
>>>> log4j2 please?
>>>> Im trying to update gerrit to log4j2 but am stuck on some things. [1]
>>>> 1. How do i migrate from 
>>>> PropertyConfigurator.configure(Loader.getResource(LOG_CONFIGURATION)); to 
>>>> something log4j2 compatible please?
>>>> Im trying to migrate all the way without trying to use log4j1 compatible 
>>>> api log4j2. (Though im still pulling it in i am trying not to use it).
>>>> I found doing something like
>>>>     String path = System.getProperty(JAVA_OPTIONS_LOG_CONFIG);    if 
>>>> (Strings.isNullOrEmpty(path)) {      ConfigurationSource source = 
>>>> ConfigurationSource.fromResource(LOG_CONFIGURATION, null);      
>>>> Configurator.initialize(null, source);    } else {      URL in = new 
>>>> URL(path);      Configurator.initialize((String) null, null, in.toURI());  
>>>>   }
>>>> could work but then it wont reload the configuation without restarting the 
>>>> configuation as new (ie gets rid of everything). which .reconfigure() does.
>>>> Im trying to reset log levels to null so that we can reload the 
>>>> configuation but reconfigure gets rid of everything thus causing problems 
>>>> if you used java to add appenders or anything else. see [2]
>>>> Also how would i migrate from using removeAllAppenders to log4j2 
>>>> compatible code please?
>>>> [1] 
>>>> <>
>>>> [2] 
>>>> <>
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