MDC 优雅的追踪日志方案

追踪日志

通过什么方式，可以在logger的输出结果上自动附加一个标识？
日常开发中，为了能够快速定位问题，通常需要在日志中记录请求url，请求方法，用户ID，请求ID等等等等。硬编码的形式log.info("requestUrl:{}, userId: {}......", requestUrl, userId)；显然是无法满足要求的，这样实现工作量大，易出错，改动也极其不便。

解决方案

使用MDC只需要几行代码就能轻松应对上述需求。实现一个Filter，使用MDC.put(key, val)写入需要打印的参数。

import org.slf4j.MDC;

public class MDCFilter extends OncePerRequestFilter implements Filter {

    @Override
    protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain) throws
            IOException,
            ServletException {
        
        try {
            MDC.put("requestMethod", request.getMethod().toUpperCase());
            MDC.put("requestUri", request.getRequestURI());
            MDC.put("uuid", UUID.randomUUID().toString().replace("-", ""));
            MDC.put("ip", request.getRemoteAddr());
            User requestUser = (User) request.getAttribute(Constants.REQUEST_USER);
            if (requestUser != null) {
                MDC.put("uid", String.valueOf(requestUser.getId()));
            }
        } catch (Exception e) {
            logger.error("init MDC error.", e);
        }
        try {
            filterChain.doFilter(request, response);
        } finally {
            MDC.clear();
        }
    }
}

注册Filter

    @Bean
    public FilterRegistrationBean<MDCFilter> mdcFilter() {
        FilterRegistrationBean<MDCFilter> registrationBean = new FilterRegistrationBean<>();
        registrationBean.setName("mdcFilter");

        MDCFilter mdcFilter = new MDCFilter();
        registrationBean.setFilter(mdcFilter);
        registrationBean.addUrlPatterns("/*");
        registrationBean.setOrder(100);
        return registrationBean;
    }

日志pattern配置，使用%X{} 取值。%X{requestMethod} %X{requestUri} %X{uuid} %X{uid}

<appender name="INFO_FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">

    <file>${log.path}/log.log</file>

    <encoder>
        <pattern>
            %d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level %X{requestMethod} %X{requestUri} %X{uuid} %X{uid} %logger{50} - %msg%n
        </pattern>
        <charset>UTF-8</charset>
    </encoder>

    <rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">
        
        <fileNamePattern>${log.path}/info/log-info-%d{yyyy-MM-dd}.%i.log</fileNamePattern>
        <timeBasedFileNamingAndTriggeringPolicy class="ch.qos.logback.core.rolling.SizeAndTimeBasedFNATP">
            <maxFileSize>10MB</maxFileSize>
        </timeBasedFileNamingAndTriggeringPolicy>
        
        <maxHistory>15</maxHistory>
    </rollingPolicy>
</appender>

打印效果

2020-05-23 01:59:27.028  INFO POST /api/login 5a7fa16b42e44f1395678f77fbbcad92  17552 

最后附上文档 MDC文档