聊聊logback的LevelFilter

序

本文主要研究一下logback的LevelFilter

AbstractMatcherFilter

ch/qos/logback/core/filter/AbstractMatcherFilter.java

public abstract class AbstractMatcherFilter<E> extends Filter<E> {

    protected FilterReply onMatch = FilterReply.NEUTRAL;
    protected FilterReply onMismatch = FilterReply.NEUTRAL;

    final public void setOnMatch(FilterReply reply) {
        this.onMatch = reply;
    }

    final public void setOnMismatch(FilterReply reply) {
        this.onMismatch = reply;
    }

    final public FilterReply getOnMatch() {
        return onMatch;
    }

    final public FilterReply getOnMismatch() {
        return onMismatch;
    }
}

AbstractMatcherFilter继承了Filter，它定义了onMatch及onMismatch属性

LevelFilter

ch/qos/logback/classic/filter/LevelFilter.java

public class LevelFilter extends AbstractMatcherFilter<ILoggingEvent> {

    Level level;

    @Override
    public FilterReply decide(ILoggingEvent event) {
        if (!isStarted()) {
            return FilterReply.NEUTRAL;
        }

        if (event.getLevel().equals(level)) {
            return onMatch;
        } else {
            return onMismatch;
        }
    }

    public void setLevel(Level level) {
        this.level = level;
    }

    public void start() {
        if (this.level != null) {
            super.start();
        }
    }
}

LevelFilter继承了AbstractMatcherFilter，其decide判断event的level等级是否与配置的level一致，一致则返回onMatch，否则返回onMismatch

示例

    <appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
        <filter class="ch.qos.logback.classic.filter.LevelFilter">
            <level>ERROR</level>
            <onMatch>ACCEPT</onMatch>
            <onMismatch>DENY</onMismatch>
        </filter>
        <encoder>
            <pattern>${CONSOLE_LOG_PATTERN}</pattern>
        </encoder>
    </appender>

这里CONSOLE的appender定义了LevelFilter，当level为ERROR级别时ACCEPT，否则DENY

小结

logback提供了LevelFilter，可以配置指定的level、onMatch、onMismatch属性，用于设置指定appender的打印级别。