聊聊logback的MDCFilter

序

本文主要研究一下logback的MDCFilter

MatchingFilter

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

public abstract class MatchingFilter extends TurboFilter {protected FilterReply onMatch = FilterReply.NEUTRAL;protected FilterReply onMismatch = FilterReply.NEUTRAL;final public void setOnMatch(String action) {if ("NEUTRAL".equals(action)) {onMatch = FilterReply.NEUTRAL;} else if ("ACCEPT".equals(action)) {onMatch = FilterReply.ACCEPT;} else if ("DENY".equals(action)) {onMatch = FilterReply.DENY;}}final public void setOnMismatch(String action) {if ("NEUTRAL".equals(action)) {onMismatch = FilterReply.NEUTRAL;} else if ("ACCEPT".equals(action)) {onMismatch = FilterReply.ACCEPT;} else if ("DENY".equals(action)) {onMismatch = FilterReply.DENY;}}
}

MatchingFilter继承了TurboFilter，它提供了setOnMatch及setOnMismatch方法，它们在action为NEUTRAL、ACCEPT、DENY时设置对应的onMatch、onMismatch

MDCFilter

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

public class MDCFilter extends MatchingFilter {String MDCKey;String value;@Overridepublic void start() {int errorCount = 0;if (value == null) {addError("\'value\' parameter is mandatory. Cannot start.");errorCount++;}if (MDCKey == null) {addError("\'MDCKey\' parameter is mandatory. Cannot start.");errorCount++;}if (errorCount == 0)this.start = true;}@Overridepublic FilterReply decide(Marker marker, Logger logger, Level level, String format, Object[] params, Throwable t) {if (!isStarted()) {return FilterReply.NEUTRAL;}String value = MDC.get(MDCKey);if (this.value.equals(value)) {return onMatch;}return onMismatch;}public void setValue(String value) {this.value = value;}public void setMDCKey(String MDCKey) {this.MDCKey = MDCKey;}}

MDCFilter继承了MatchingFilter，其start方法校验MDCKey及value属性是否有值，其decide方法跟从MDC获取指定key的值，然后判断该值域value是否相等，相等则返回onMatch，否则返回onMismatch

示例

<?xml version="1.0" encoding="UTF-8" ?><configuration><turboFilter class="ch.qos.logback.classic.turbo.MDCFilter"><MDCKey>username</MDCKey><Value>sebastien</Value><OnMatch>ACCEPT</OnMatch></turboFilter><turboFilter class="ch.qos.logback.classic.turbo.MarkerFilter"><Marker>billing</Marker><OnMatch>DENY</OnMatch></turboFilter><appender name="console" class="ch.qos.logback.core.ConsoleAppender"><layout class="ch.qos.logback.classic.PatternLayout"><Pattern>%date [%thread] %-5level %logger - %msg%n</Pattern></layout></appender><root level="info"><appender-ref ref="console" /></root>
</configuration>

小结

logback提供了MDCFilter，它可以根据指定的MDCKey从MDC取值，然后根据配置的value进行判断，然后执行onMatch或者onMismatch来决定是否打印日志。