java log4j

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### Logger hierarchy

  • Named Hierarchy
    A logger is said to be an ancestor of another logger if its name followed by a dot is a prefix of the descendant logger name. A logger is said to be a parent of a child logger if there are no ancestors between itself and the descendant logger.
  • root logger
  1. it always exists,
  2. it cannot be retrieved by name.
  • Level Inheritance
    The inherited level for a given logger C, is equal to the first non-null level in the logger hierarchy, starting at C and proceeding upwards in the hierarchy towards the root logger.
  • Basic Selection Rule
    A log request of level p in a logger with (either assigned or inherited, whichever is appropriate) level q, is enabled if p >= q.
    DEBUG < INFO < WARN < ERROR < FATAL.
// get a logger instance named "com.foo"
Logger  logger = Logger.getLogger("com.foo");

// Now set its level. Normally you do not need to set the
// level of a logger programmatically. This is usually done
// in configuration files.
logger.setLevel(Level.INFO);

Logger barlogger = Logger.getLogger("com.foo.Bar");

// This request is enabled, because WARN >= INFO.
logger.warn("Low fuel level.");

// This request is disabled, because DEBUG < INFO.
logger.debug("Starting search for nearest gas station.");

// The logger instance barlogger, named "com.foo.Bar",
// will inherit its level from the logger named
// "com.foo" Thus, the following request is enabled
// because INFO >= INFO.
barlogger.info("Located nearest gas station.");

// This request is disabled, because DEBUG < INFO.
barlogger.debug("Exiting gas station search");

### Appenders
More than one appender can be attached to a logger.
Each enabled logging request for a given logger will be forwarded to all the appenders in that logger as well as the appenders higher in the hierarchy.

  • Appender Additivity
    The output of a log statement of logger C will go to all the appenders in C and its ancestors. This is the meaning of the term "appender additivity".
However, if an ancestor of logger C, say P, has the additivity flag set to false, then C's output will be directed to all the appenders in C and its ancestors upto and including P but not the appenders in any of the ancestors of P.

Loggers have their additivity flag set to true by default.

log4j.additivity.logName = false
or

log.setAdditivity(false);

### PatternLayout

Each conversion specifier starts with a percent sign (%) and is followed by optional format modifiers and a conversion character.

  1. The conversion character specifies the type of data, e.g. category, priority, date, thread name.
  2. The format modifiers control such things as field width, padding, left and right justification.
    %-5p means the priority of the logging event should be left justified to a width of five characters
  • Conversion Character

Conversion Character
### Configuration

  • BasicConfigurator.configure();
  1. creates a rather simple log4j setup
  2. add to the root logger a ConsoleAppender
  3. The output will be formatted using a PatternLayout set to the pattern "%-4r [%t] %-5p %c %x - %m%n"
  4. by default, the root logger is assigned to Level.DEBUG
    ### Properties
    ${} from System.properties or Log4j.props
    ### threshold
    修改某个logger其中一个appender的level
    log4j.appender.R2.threshold=WARN

### example

log4j.rootLogger=INFO,R,stdout

log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=[%-5p] %d{yyyy-MM-dd HH:mm:ss,SSS} method:%l%n%m%n


log4j.appender.R=org.apache.log4j.RollingFileAppender
log4j.appender.R.File=${etl.log}/root.log
log4j.appender.R.MaxFileSize=25MB
log4j.appender.R.MaxBackupIndex=1
log4j.appender.R.layout=org.apache.log4j.PatternLayout
log4j.appender.R.layout.ConversionPattern=[%-5p] %d{yyyy-MM-dd HH:mm:ss,SSS} method:%l%n%m%n

log4j.logger.xdata.etl.kafka.consumer.Consumer=INFO,C1,C2

log4j.appender.C1=org.apache.log4j.RollingFileAppender
log4j.appender.C1.File=${etl.log}/consumer/info.log
log4j.appender.C1.MaxFileSize=25MB
log4j.appender.C1.MaxBackupIndex=1
log4j.appender.C1.layout=org.apache.log4j.PatternLayout
log4j.appender.C1.layout.ConversionPattern=[%-5p]\t[%d{yyyy-MM-dd HH:mm:ss,SSS}]\t[%r]\t%F\t%m%n

log4j.appender.C2.threshold=WARN
log4j.appender.C2=org.apache.log4j.RollingFileAppender
log4j.appender.C2.File=${etl.log}/consumer/error.log
log4j.appender.C2.MaxFileSize=25MB
log4j.appender.C2.MaxBackupIndex=1
log4j.appender.C2.layout=org.apache.log4j.PatternLayout
log4j.appender.C2.layout.ConversionPattern=[%-5p]\t[%d{yyyy-MM-dd HH:mm:ss,SSS}]\t[%r]\t%F\t%m%n