log4j源码阅读（一）之Logger

 1   /**
 2      Starting from this category, search the category hierarchy for a
 3      non-null level and return it. Otherwise, return the level of the
 4      root category.
 5 
 6      <p>The Category class is designed so that this method executes as
 7      quickly as possible.
 8    */
 9   public
10   Level getEffectiveLevel() {
11     for(Category c = this; c != null; c=c.parent) {
12       if(c.level != null) {
13         return c.level;
14     }
15     }
16     return null; // If reached will cause an NullPointerException.
17   }

  /**
     Add <code>newAppender</code> to the list of appenders of this
     Category instance.

     <p>If <code>newAppender</code> is already in the list of
     appenders, then it won‘t be added again.
  */
  synchronized
  public
  void addAppender(Appender newAppender) {
    if(aai == null) {
      aai = new AppenderAttachableImpl();
    }
    aai.addAppender(newAppender);
    repository.fireAddAppenderEvent(this, newAppender);
  }

  /**
     Attach an appender. If the appender is already in the list in
     won‘t be added again.
  */
  public
  void addAppender(Appender newAppender) {
    // Null values for newAppender parameter are strictly forbidden.
    if(newAppender == null) {
        return;
    }
    
    if(appenderList == null) {
      appenderList = new Vector(1);
    }
    if(!appenderList.contains(newAppender)) {
        appenderList.addElement(newAppender);
    }
  }

  public
  void debug(Object message) {
    if(repository.isDisabled(Level.DEBUG_INT)) {
        return;
    }
    if(Level.DEBUG.isGreaterOrEqual(this.getEffectiveLevel())) {
      forcedLog(FQCN, Level.DEBUG, message, null);
    }
  }

  /**
     This method creates a new logging event and logs the event
     without further checks.  */
  protected
  void forcedLog(String fqcn, Priority level, Object message, Throwable t) {
    callAppenders(new LoggingEvent(fqcn, this, level, message, t));
  }

  public
  void callAppenders(LoggingEvent event) {
    int writes = 0;

    for(Category c = this; c != null; c=c.parent) {
      // Protected against simultaneous call to addAppender, removeAppender,...
      synchronized(c) {
    if(c.aai != null) {
      writes += c.aai.appendLoopOnAppenders(event);
    }
    if(!c.additive) {
      break;
    }
      }
    }

    if(writes == 0) {
      repository.emitNoAppenderWarning(this);
    }
  }

  public
  void debug(Object message) {
    if(repository.isDisabled(Level.DEBUG_INT)) {
        return;
    }
...

  public
  boolean isDisabled(int level) {
    return thresholdInt > level;
  }

 public
  synchronized 
  void doAppend(LoggingEvent event) {
    if(closed) {
      LogLog.error("Attempted to append to closed appender named ["+name+"].");
      return;
    }
    
    if(!isAsSevereAsThreshold(event.getLevel())) {
      return;
    }

    Filter f = this.headFilter;
    
    FILTER_LOOP:
    while(f != null) {
      switch(f.decide(event)) {
      case Filter.DENY: return;
      case Filter.ACCEPT: break FILTER_LOOP;
      case Filter.NEUTRAL: f = f.getNext();
      }
    }
    
    this.append(event);    
  }

  static {
    // By default we use a DefaultRepositorySelector which always returns ‘h‘.
    Hierarchy h = new Hierarchy(new RootLogger(Level.DEBUG));
    repositorySelector = new DefaultRepositorySelector(h);
}

public static Logger LOG = LogManager.getLogger(TestMain.class);