聊聊logback的addtivity属性

序

本文主要研究一下logback的addtivity属性

LoggerModel

ch/qos/logback/classic/model/LoggerModel.java

@PhaseIndicator(phase = ProcessingPhase.SECOND)
public class LoggerModel extends Model {

    private static final long serialVersionUID = 5326913660697375316L;

    String name;
    String level;
    String additivity;

    //......
}    

LoggerModel定义了additivity属性

LoggerAction

ch/qos/logback/classic/joran/action/LoggerAction.java

public class LoggerAction extends BaseModelAction {

    @Override
    protected boolean validPreconditions(SaxEventInterpretationContext ic, String name, Attributes attributes) {
        PreconditionValidator validator = new PreconditionValidator(this, ic, name, attributes);
        validator.validateNameAttribute();
        return validator.isValid();
    }

    @Override
    protected Model buildCurrentModel(SaxEventInterpretationContext interpretationContext, String name,
            Attributes attributes) {

        LoggerModel loggerModel = new LoggerModel();

        String nameStr = attributes.getValue(NAME_ATTRIBUTE);
        loggerModel.setName(nameStr);

        String levelStr = attributes.getValue(JoranConstants.LEVEL_ATTRIBUTE);
        loggerModel.setLevel(levelStr);

        String additivityStr = attributes.getValue(JoranConstants.ADDITIVITY_ATTRIBUTE);
        loggerModel.setAdditivity(additivityStr);

        return loggerModel;
    }
}

LoggerAction的buildCurrentModel方法会读取additivity属性，然后设置到loggerModel

LoggerModelHandler

ch/qos/logback/classic/model/processor/LoggerModelHandler.java

public class LoggerModelHandler extends ModelHandlerBase {

    Logger logger;
    boolean inError = false;

    //......

    @Override
    public void handle(ModelInterpretationContext mic, Model model) throws ModelHandlerException {
        inError = false;

        LoggerModel loggerModel = (LoggerModel) model;

        String finalLoggerName = mic.subst(loggerModel.getName());

        LoggerContext loggerContext = (LoggerContext) this.context;

        logger = loggerContext.getLogger(finalLoggerName);

        String levelStr = mic.subst(loggerModel.getLevel());
        if (!OptionHelper.isNullOrEmpty(levelStr)) {
            if (JoranConstants.INHERITED.equalsIgnoreCase(levelStr) || NULL.equalsIgnoreCase(levelStr)) {
                if(Logger.ROOT_LOGGER_NAME.equalsIgnoreCase(finalLoggerName)) {
                    addError(ErrorCodes.ROOT_LEVEL_CANNOT_BE_SET_TO_NULL);
                } else {
                    addInfo("Setting level of logger [" + finalLoggerName + "] to null, i.e. INHERITED");
                    logger.setLevel(null);
                }
            } else {
                Level level = Level.toLevel(levelStr);
                addInfo("Setting level of logger [" + finalLoggerName + "] to " + level);
                logger.setLevel(level);
            }
        }

        String additivityStr = mic.subst(loggerModel.getAdditivity());
        if (!OptionHelper.isNullOrEmpty(additivityStr)) {
            boolean additive = OptionHelper.toBoolean(additivityStr, true);
            addInfo("Setting additivity of logger [" + finalLoggerName + "] to " + additive);
            logger.setAdditive(additive);
        }

        mic.pushObject(logger);
    }

    //......
}    

LoggerModelHandler的handle方法会读取additivityStr，然后设置到logger中

Logger

ch/qos/logback/classic/Logger.java

public final class Logger
        implements org.slf4j.Logger, LocationAwareLogger, LoggingEventAware, AppenderAttachable, Serializable {

    //......

    /**
     * The parent of this category. All categories have at least one ancestor which
     * is the root category.
     */
    transient private Logger parent;

    /**
     * Additivity is set to true by default, that is children inherit the appenders
     * of their ancestors by default. If this variable is set to false
     * then the appenders located in the ancestors of this logger will not be used.
     * However, the children of this logger will inherit its appenders, unless the
     * children have their additivity flag set to false too. See the
     * user manual for more details.
     */
    transient private boolean additive = true;

    //......

    public void callAppenders(ILoggingEvent event) {
        int writes = 0;
        for (Logger l = this; l != null; l = l.parent) {
            writes += l.appendLoopOnAppenders(event);
            if (!l.additive) {
                break;
            }
        }
        // No appenders in hierarchy
        if (writes == 0) {
            loggerContext.noAppenderDefinedWarning(this);
        }
    }

    void recursiveReset() {
        detachAndStopAllAppenders();
        localLevelReset();
        additive = true;
        if (childrenList == null) {
            return;
        }
        for (Logger childLogger : childrenList) {
            childLogger.recursiveReset();
        }
    }

    //......
}        

Logger的callAppenders方法会先打印自己的appender，然后逐层遍历parent进行打印，若additive为false则不通过parent的appender打印

小结

logback的Logger提供了addtivity属性，默认为true，即除了自己appender，还会通过parent的appender进行打印，设置为false则不通过parent的appender进行打印。