序

本文主要研究一下logback的DynamicThresholdFilter

DynamicThresholdFilter

public class DynamicThresholdFilter extends TurboFilter {private Map<String, Level> valueLevelMap = new HashMap<String, Level>();private Level defaultThreshold = Level.ERROR;private String key;private FilterReply onHigherOrEqual = FilterReply.NEUTRAL;private FilterReply onLower = FilterReply.DENY;//......
}    

DynamicThresholdFilter继承了TurboFilter，它定义了valueLevelMap、defaultThreshold为ERROR，onHigherOrEqual为NEUTRAL，onLower为DENY

addMDCValueLevelPair

    public void addMDCValueLevelPair(MDCValueLevelPair mdcValueLevelPair) {if (valueLevelMap.containsKey(mdcValueLevelPair.getValue())) {addError(mdcValueLevelPair.getValue() + " has been already set");} else {valueLevelMap.put(mdcValueLevelPair.getValue(), mdcValueLevelPair.getLevel());}}    

addMDCValueLevelPair方法可以根据MDCValueLevelPair往valueLevelMap添加配置

MDCValueLevelPair

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

public class MDCValueLevelPair {private String value;private Level level;public String getValue() {return value;}public void setValue(String name) {this.value = name;}public Level getLevel() {return level;}public void setLevel(Level level) {this.level = level;}
}

MDCValueLevelPair定义了value及level属性

decide

    public FilterReply decide(Marker marker, Logger logger, Level level, String s, Object[] objects,Throwable throwable) {String mdcValue = MDC.get(this.key);if (!isStarted()) {return FilterReply.NEUTRAL;}Level levelAssociatedWithMDCValue = null;if (mdcValue != null) {levelAssociatedWithMDCValue = valueLevelMap.get(mdcValue);}if (levelAssociatedWithMDCValue == null) {levelAssociatedWithMDCValue = defaultThreshold;}if (level.isGreaterOrEqual(levelAssociatedWithMDCValue)) {return onHigherOrEqual;} else {return onLower;}}

decide方法先从mdc获取key对应的mdcValue，然后根据mdcValue去valueLevelMap获取对应的level，如果获取不到则取defaultThreshold；如果要打印的level大于等于levelAssociatedWithMDCValue则返回NEUTRAL，否则返回DENY

示例

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration><configuration><turboFilter class="ch.qos.logback.classic.turbo.DynamicThresholdFilter"><Key>userId</Key><DefaultThreshold>ERROR</DefaultThreshold><MDCValueLevelPair><value>user1</value><level>INFO</level></MDCValueLevelPair><MDCValueLevelPair><value>user2</value><level>TRACE</level></MDCValueLevelPair></turboFilter><appender name="LIST"class="ch.qos.logback.core.read.ListAppender"></appender><root><level value="DEBUG" /><appender-ref ref="LIST" /></root>
</configuration>

小结

logback提供了DynamicThresholdFilter，它可以根据配置的key从MDC取值，再根据配置的MDCValueLevelPair去映射对应的level，达到动态log级别的效果。