log4j中同一日志文件中的多个日志级别

Question

How can multiple log levels added to the same log file in log4j? For example:

log4j.rootLogger=INFO,WARN,stdout,file

It gives the log4j error when application start as:

Could not instantiate appender named WARN.

Answer 1

The purpose of the threshold is to tell log4j to ignore all logging requests with a priority lower than what you specify. Specifying a given threshold does not limit you to logging with that threshold.

FileAppender fa = new FileAppender();
fa.setThreshold(Level.INFO);
fa.setAppend(true);
Logger.getRootLogger().addAppender(fa);

In the above code, the appender has been configured to operate with a threshold of INFO . This means that the following code will not log, because DEBUG is a lower priority than INFO :

Logger logger = Logger.getLogger(SomeClass.class);
logger.debug("This will not log");

But this code will log:

logger.warn("This debug message will log.");
logger.error("And this error message will also log.");

In this case, both WARN and ERROR have a higher priority than INFO .