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176 [main] INFO  org.foo.Bar - Located nearest gas station.

    %c 輸出日誌訊息所屬的類別的全名
    %d 輸出日誌時間點的日期或時間，指定格式的方式：%d{yyy-MM-dd HH:mm:ss }。
    %l 輸出日誌事件的發生位置，即輸出日誌訊息的語句處於它所在的類別的第幾行。
    %m 輸出代碼中指定的訊息，如log(message)中的message。
    %n 輸出一個列尾符號。
    %p 輸出優先階層，即DEBUG，INFO，WARN，ERROR，FATAL。如果是調用debug()輸出的，則為DEBUG，依此類推。-5p 代表將此字串填滿至 5 個字元,以空白補不足處。
    %r 輸出自應用啟動到輸出該日誌訊息所耗費的毫秒數。
    %t 輸出產生該日誌事件的線程名。
    %f 輸出日誌訊息所屬的類別的類別名。

package yc.usingLog4j;

import org.apache.log4j.BasicConfigurator;
import org.apache.log4j.Logger;

public class UsingLog4j {
     private static Logger logger = Logger.getLogger(UsingLog4j.class);

     public static void main(String[] args) {
     BasicConfigurator.configure();

     logger.info("This is an info message.");
     logger.debug("This is a debug message.");
 }
}

#定義 Root Logger 的等級為 INFO,且為其指定一個 appender 名為 rootAppender.
log4j.rootLogger=info, rootAppender

#指定 rootAppender 的類型.
log4j.appender.rootAppender=org.apache.log4j.ConsoleAppender

#指定 rootAppender 的 Layout.
log4j.appender.rootAppender.layout=org.apache.log4j.PatternLayout

#指定 rootAppender Layout 的輸出格式.
log4j.appender.rootAppender.layout.ConversionPattern=%d [%t] %-5p %c - %m%n

#設定特定名稱的 Logger.
log4j.logger.yc.usingLog4j.UsingLog4jA=INFO, log4jaAppender
log4j.appender.log4jaAppender=org.apache.log4j.RollingFileAppender
log4j.appender.log4jaAppender.File=d:/tmp/usinglog4j.log
log4j.appender.log4jaAppender.MaxFileSize=100KB
log4j.appender.log4jaAppender.MaxBackupIndex=10
log4j.appender.log4jaAppender.layout=org.apache.log4j.PatternLayout
log4j.appender.log4jaAppender.layout.ConversionPattern=%c - %m%n

package yc.usingLog4j;

import org.apache.log4j.BasicConfigurator;
import org.apache.log4j.Level;
import org.apache.log4j.Logger;

public class UsingLog4j {
  private static Logger logger = Logger.getLogger(UsingLog4j.class);

  public static void main(String[] args) {
      BasicConfigurator.configure();

      /* 改變 Root Logger 的等級為 INFO */
      //Logger.getRootLogger().setLevel(Level.INFO);

      /* 鴨子類別庫的 client 只做 INFO 等級的 log;類別庫裡才使用 DEBUG 等級的 log. */
      logger.info("Create a Redhead Duck.");
      RedheadDuck rhd = new RedheadDuck(new FlyWithWings(), new Quack());
      logger.info("Play with the duck.");
      rhd.display();
      rhd.performFly();
      rhd.performQuack();

      logger.info("Create a RubberDuck.");
      RubberDuck rbd = new RubberDuck(new FlyWithRocket(), new Squeak());
      logger.info("Play with the duck.");
      rbd.display();
      rbd.performFly();
      rbd.performQuack();
      }
  }

  interface FlyBehavior {
      public void fly();
  }

  class FlyWithWings implements FlyBehavior {
      private static Logger logger = Logger.getLogger(FlyWithWings.class);

      public void fly() {
      logger.debug("Fly with wings...");
  }
}

class FlyWithRocket implements FlyBehavior {
  private static Logger logger = Logger.getLogger(FlyWithRocket.class);

  public void fly() {
      logger.debug("Fly with a rocket...");
  }
}

interface QuackBehavior {
  public void quack();
}

class Quack implements QuackBehavior {
  private static Logger logger = Logger.getLogger(Quack.class);

  public void quack() {
      logger.debug("Quack...");
  }
}

class Squeak implements QuackBehavior {
  private static Logger logger = Logger.getLogger(Squeak.class);

  public void quack() {
      logger.debug("Squeak...");
  }
}

abstract class Duck {
  private FlyBehavior flyBehavior;

  private QuackBehavior quackBehavior;

  public Duck(FlyBehavior flyBehavior, QuackBehavior quackBehavior) {
      this.flyBehavior = flyBehavior;
      this.quackBehavior = quackBehavior;
  }

  public void performQuack() {
      this.quackBehavior.quack();
  }

  public void performFly() {
   this.flyBehavior.fly();
  }

  public abstract void display();
}

class RedheadDuck extends Duck {
  private static Logger logger = Logger.getLogger(RedheadDuck.class);

  public RedheadDuck(FlyBehavior flyBehavior, QuackBehavior quackBehavior) {
      super(flyBehavior, quackBehavior);
  }

  @Override
  public void display() {
      logger.debug("A RedheadDuck is showing up...");
  }
}

class RubberDuck extends Duck {
  private static Logger logger = Logger.getLogger(RubberDuck.class);

  public RubberDuck(FlyBehavior flyBehavior, QuackBehavior quackBehavior) {
      super(flyBehavior, quackBehavior);
  }

  @Override
  public void display() {
      logger.debug("A RubberDuck is showing up...");
  }
}

0 [main] INFO yc.usingLog4j.UsingLog4j  - Create a Redhead Duck.
16 [main] INFO yc.usingLog4j.UsingLog4j  - Play with the duck.
16 [main] INFO yc.usingLog4j.UsingLog4j  - Create a RubberDuck.
16 [main] INFO yc.usingLog4j.UsingLog4j  - Play with the duck.

0 [main] INFO yc.usingLog4j.UsingLog4j  - Create a Redhead Duck.
109 [main] INFO yc.usingLog4j.UsingLog4j  - Play with the duck.
109 [main] DEBUG yc.usingLog4j.RedheadDuck  - A RedheadDuck is showing up...
109 [main] DEBUG yc.usingLog4j.FlyWithWings  - Fly with wings...
109 [main] DEBUG yc.usingLog4j.Quack  - Quack...
109 [main] INFO yc.usingLog4j.UsingLog4j  - Create a RubberDuck.
125 [main] INFO yc.usingLog4j.UsingLog4j  - Play with the duck.
125 [main] DEBUG yc.usingLog4j.RubberDuck  - A RubberDuck is showing up...
125 [main] DEBUG yc.usingLog4j.FlyWithRocket  - Fly with a rocket...
125 [main] DEBUG yc.usingLog4j.Squeak  - Squeak...