logback使用MDCFilter日志过滤源码解读

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;
        }
    }
}

public class MDCFilter extends MatchingFilter {
    String MDCKey;
    String value;
    @Override
    public 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;
    }
    @Override
    public 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;
    }
}

<?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>