How about log4j-core's Configurator class and its setLevel() methods?
Gary
On Tue, Feb 28, 2023, 14:04 Christopher Schultz <
ch...@christopherschultz.net> wrote:
> All,
>
> I'm coming from a log4j v1.x background where this was easy to do:
>
> String loggerName = "com.example.Class";
> Logger log = LogManager.exists(loggerName);
> if(null != log) {
> log.setLevel(targetLevel);
> }
>
> This appears no longer to be possible -- or at least easy -- and I've
> seen at least two techniques on StackOverflow which result in the same
> behavior: the log-level threshold for *every logger everywhere* gets set
> to the target level.
>
> For example, setting the log-level for the logger called "foo" to TRACE
> ends up filling my log with stuff from completely unrelated
> loggers/classes/etc.
>
> Here is one technique[1]
>
> String loggerName = "com.example.Class";
> LoggerContext ctx = (LoggerContext) LogManager.getContext(false);
> Configuration config = ctx.getConfiguration();
> LoggerConfig loggerConfig = config.getLoggerConfig(loggerName);
> loggerConfig.setLevel(level);
> ctx.updateLoggers(); // This causes all Loggers to refetch information
> from their LoggerConfig.
>
> I tried both with and without the ctx.updateLoggers() call.
>
> Here is another technique[2]:
>
> Configurator.setLevel(loggerName, level);
>
> This reconfigures everything just like the one above.
>
> The final technique (still in the same SO question) is this:
>
> final LoggerContext ctx = (LoggerContext)
> LogManager.getContext(false);
> final Configuration config = ctx.getConfiguration();
>
> LoggerConfig loggerConfig = config.getLoggerConfig(logger.getName());
> LoggerConfig specificConfig = loggerConfig;
>
> // We need a specific configuration for this logger,
> // otherwise we would change the level of all other loggers
> // having the original configuration as parent as well
>
> if (!loggerConfig.getName().equals(logger.getName())) {
> specificConfig = new LoggerConfig(logger.getName(), level, true);
> specificConfig.setParent(loggerConfig);
> config.addLogger(logger.getName(), specificConfig);
> }
> specificConfig.setLevel(level);
> ctx.updateLoggers();
>
> This does not seem to set the log level for all loggers to e.g. TRACE
> but it also doesn't seem to set the actual logger. (I can see e.g. DEBUG
> and TRACE logs from other loggers, so it's not an issue with the appender).
>
> What is the recommended technique for changing a single logger's
> threshold in log4j2? I realize that the best thing to do would be to
> "just configure it correctly the first time" but in reality, you
> sometimes just have to enable TRACE logging in production to figure out
> what the hell is happening.
>
> Thanks,
> -chris
>
>
> [1] Adapted from https://stackoverflow.com/a/23434603/276232
> [2] Adapted from https://stackoverflow.com/a/44678752/276232
>
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