Logback进阶

2. Logback 源码分析

// log.info("user:{}", "tinyspot");

// slf4j
public void info(String format, Object arg);

// logback 实现：ch.qos.logback.classic.Logger#info
public void info(String format, Object arg) {
  this.filterAndLog_1(FQCN, (Marker)null, Level.INFO, format, arg, (Throwable)null);
}

private void buildLoggingEventAndAppend(String localFQCN, Marker marker, Level level, String msg, Object[] params, Throwable t) {
  LoggingEvent le = new LoggingEvent(localFQCN, this, level, msg, t, params);
  le.setMarker(marker);
  this.callAppenders(le);
}

2.1 callAppenders(ILoggingEvent event)

• appendLoopOnAppenders()
• ch.qos.logback.core.Appender#doAppend

public void callAppenders(ILoggingEvent event) {
    int writes = 0;
    for (Logger l = this; l != null; l = l.parent) {
        // Invoke all the appenders of this logger
        writes += l.appendLoopOnAppenders(event);
        if (!l.additive) {
            // 如果子logger 和 父logger 都绑定了同样的 appender, 日志会重复记录；如果不想重复记录，指定additivity="false"
            break;
        }
    }
    if (writes == 0) {
        loggerContext.noAppenderDefinedWarning(this);
    }
}

public int appendLoopOnAppenders(E e) {
    // ...
    for (int i = 0; i < len; i++) {
        appenderArray[i].doAppend(e);
        size++;
    }
}

ch.qos.logback.core.UnsynchronizedAppenderBase#doAppend

public void prepareForDeferredProcessing() {
    // format message
    this.getFormattedMessage();
    this.getThreadName();
    this.getMDCPropertyMap();
}

6. 动态构造 logger 对象

import ch.qos.logback.classic.Logger;
import ch.qos.logback.classic.LoggerContext;
import org.slf4j.LoggerFactory;

@Test
public void test() {
    // LoggerContext context = (LoggerContext) LoggerFactory.getILoggerFactory();
    // StatusPrinter.print(context);
    getLogger("org.demo").info("this is my custom logger");
}

public static Logger getLogger(String name) {
    LoggerContext loggerContext = (LoggerContext) LoggerFactory.getILoggerFactory();
    if (loggerContext.exists(name) == null) {
        Logger logger = loggerContext.getLogger(name);
        RollingFileAppender rollingFileAppender = new RollingFileAppender();
        rollingFileAppender.setName(name);
        rollingFileAppender.setContext(loggerContext);

        TimeBasedRollingPolicy rollingPolicy = new TimeBasedRollingPolicy();
        rollingPolicy.setFileNamePattern("/log/" + name + ".%d{yyyy-MM-dd}.log");
        rollingPolicy.setParent(rollingFileAppender);
        rollingPolicy.setContext(loggerContext);
        rollingPolicy.start();

        PatternLayoutEncoder encoder = new PatternLayoutEncoder();
        encoder.setCharset(StandardCharsets.UTF_8);
        encoder.setPattern("%m%n");
        encoder.setContext(loggerContext);
        encoder.start();

        rollingFileAppender.setRollingPolicy(rollingPolicy);
        rollingFileAppender.setEncoder(encoder);
        rollingFileAppender.start();

        logger.addAppender(rollingFileAppender);
        logger.setAdditive(false);
        logger.setLevel(Level.INFO);
        return logger;
    }
    return null;
}

8. Logback 的 MDC 解析

• 多线程间应用
• Mapped Diagnostic Context, 一个线程安全的存放诊断日志的容器
• 使用 MDC 之前需要在配置文件加上 %X{REQUEST}
• MDC, MDCAdapter, LogbackMDCAdapter
• 用处
  • 在日志中记录用户IP, 请求URL，统计耗时等
  • 在MDC中填充 REQUEST ID 追踪单个请求的执行轨迹
  • 微服务场景下，使用 MDC埋点，做到链路跟踪，多个系统日志的拼接