聊聊logback的DuplicateMessageFilter

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本文主要研究一下logback的DuplicateMessageFilter

TurboFilter

ch/qos/logback/classic/turbo/TurboFilter.java

public abstract class TurboFilter extends ContextAwareBase implements LifeCycle {private String name;boolean start = false;/*** Make a decision based on the multiple parameters passed as arguments. The* returned value should be one of <code>{@link FilterReply#DENY}</code>,* <code>{@link FilterReply#NEUTRAL}</code>, or* <code>{@link FilterReply#ACCEPT}</code>.* * @param marker* @param logger* @param level* @param format* @param params* @param t* @return*/public abstract FilterReply decide(Marker marker, Logger logger, Level level, String format, Object[] params,Throwable t);public void start() {this.start = true;}public boolean isStarted() {return this.start;}public void stop() {this.start = false;}public String getName() {return name;}public void setName(String name) {this.name = name;}
}

TurboFilter继承了ContextAwareBase，声明实现LifeCycle接口，它定义了decide方法由子类实现

DuplicateMessageFilter

ch/qos/logback/classic/turbo/DuplicateMessageFilter.java

public class DuplicateMessageFilter extends TurboFilter {/*** The default cache size.*/public static final int DEFAULT_CACHE_SIZE = 100;/*** The default number of allows repetitions.*/public static final int DEFAULT_ALLOWED_REPETITIONS = 5;public int allowedRepetitions = DEFAULT_ALLOWED_REPETITIONS;public int cacheSize = DEFAULT_CACHE_SIZE;private LRUMessageCache msgCache;@Overridepublic void start() {msgCache = new LRUMessageCache(cacheSize);super.start();}@Overridepublic void stop() {msgCache.clear();msgCache = null;super.stop();}@Overridepublic FilterReply decide(Marker marker, Logger logger, Level level, String format, Object[] params, Throwable t) {int count = msgCache.getMessageCountAndThenIncrement(format);if (count <= allowedRepetitions) {return FilterReply.NEUTRAL;} else {return FilterReply.DENY;}}public int getAllowedRepetitions() {return allowedRepetitions;}/*** The allowed number of repetitions before* * @param allowedRepetitions*/public void setAllowedRepetitions(int allowedRepetitions) {this.allowedRepetitions = allowedRepetitions;}public int getCacheSize() {return cacheSize;}public void setCacheSize(int cacheSize) {this.cacheSize = cacheSize;}}

DuplicateMessageFilter继承了TurboFilter，它使用了LRUMessageCache(默认大小100)来缓存format，decide方法会执行getMessageCountAndThenIncrement，若超出allowedRepetitions(默认5)则返回FilterReply.DENY，否则返回FilterReply.NEUTRAL

LRUMessageCache

ch/qos/logback/classic/turbo/LRUMessageCache.java

class LRUMessageCache extends LinkedHashMap<String, Integer> {private static final long serialVersionUID = 1L;final int cacheSize;LRUMessageCache(int cacheSize) {super((int) (cacheSize * (4.0f / 3)), 0.75f, true);if (cacheSize < 1) {throw new IllegalArgumentException("Cache size cannot be smaller than 1");}this.cacheSize = cacheSize;}int getMessageCountAndThenIncrement(String msg) {// don't insert null elementsif (msg == null) {return 0;}Integer i;// LinkedHashMap is not LinkedHashMap. See also LBCLASSIC-255synchronized (this) {i = super.get(msg);if (i == null) {i = 0;} else {i = i + 1;}super.put(msg, i);}return i;}// called indirectly by get() or put() which are already supposed to be// called from within a synchronized blockprotected boolean removeEldestEntry(Map.Entry<String, Integer> eldest) {return (size() > cacheSize);}@Overridesynchronized public void clear() {super.clear();}
}

LRUMessageCache继承了LinkedHashMap，其初始size为cacheSize * (4.0f / 3)，getMessageCountAndThenIncrement方法内部通过synchronized加锁获取指定msg的次数，不存在则设置为0，存在则递增；其removeEldestEntry方法判断size() > cacheSize

小结

DuplicateMessageFilter继承了TurboFilter，它使用了LRUMessageCache(默认大小100)来缓存format，decide方法会执行getMessageCountAndThenIncrement，若超出allowedRepetitions(默认5)则返回FilterReply.DENY，否则返回FilterReply.NEUTRAL。