动态日志调整

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项目上线后，在出现问题时经常需要查线上日志，特殊情况需要查看debug级别日志才能找到问题，这就需要能动态调整日志。

日志链路记录

日志配置文件中添加添加traceId

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<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN">
    <Appenders>
        <Console name="Console" target="SYSTEM_OUT">
            <PatternLayout pattern="%d{yyyy-MM-dd HH:mm:ss} [%t] %-5level %logger{36} %X{traceId} - %msg%n"/>
        </Console>
    </Appenders>
    <Loggers>
        <Root level="info">
            <AppenderRef ref="Console"/>
        </Root>
        <Logger name="com.whhxz.blogexample.log4j2.trace" level="info" additivity="false">
            <AppenderRef ref="Console"/>
        </Logger>
    </Loggers>
</Configuration>

在拦截器里向MDC添加traceId

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@SuppressWarnings({"UastIncorrectHttpHeaderInspection", "NullableProblems"})
public class LogTraceInterceptor implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        String traceId = request.getHeader("x-trace-id");
        if (traceId == null || traceId.isEmpty()) {
            traceId = UUID.randomUUID().toString().replace("-", "").substring(0, 12);
        }

        MDC.put("traceId", traceId);
        //此处只能设置在这里，不能设置在postHandler和afterCompletion里
        //因为那时候response可能已经返回了，再设置无效
        response.addHeader("x-trace-id", traceId);
        return true;
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        MDC.remove("traceId");
    }
}

除了在拦截器里面处理还可以在Filter里面处理。

通过DynamicThresholdFilter调整日志级别

希望请求Header添加某个参数时能调整当前线程的日志级别，在DynamicThresholdFilter中可以配置。

xml中配置Filter

在Configuration节点下添加

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<DynamicThresholdFilter key="x-log-level" defaultThreshold="INFO" onMatch="ACCEPT" onMismatch="NEUTRAL">
    <KeyValuePair key="trace" value="TRACE"/>
    <KeyValuePair key="debug" value="DEBUG"/>
</DynamicThresholdFilter>

上面表示从ThreadContext获取x-log-level，如果匹配了就接受，不匹配不处理，也可配置DENY阻塞。
如果匹配了KeyValuePair中配置的key，那么使用对应的日志。

同样配置拦截器

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@SuppressWarnings("NullableProblems")
public class DynamicLogLevelInterceptor implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        String logLevel = request.getHeader("x-log-level");
        if (logLevel != null && !logLevel.isEmpty()) {
            MDC.put("x-log-level", logLevel.toLowerCase(Locale.ROOT));
        }
        return true;
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        MDC.remove("x-log-level");
    }
}

上面设置x-log-level和xml中配置的一样，然后定义日志级别。

Java中配置Filter

在有时候，不方便直接修改xml，可以通过Java代码添加Filter

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import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import org.apache.logging.log4j.Level;
import org.apache.logging.log4j.core.Filter;
import org.apache.logging.log4j.core.LoggerContext;
import org.apache.logging.log4j.core.filter.DynamicThresholdFilter;
import org.apache.logging.log4j.core.util.KeyValuePair;
import org.slf4j.MDC;
import org.springframework.web.servlet.HandlerInterceptor;

import java.util.Locale;

@SuppressWarnings("NullableProblems")
public class DynamicLogLevelInterceptor implements HandlerInterceptor {

    private final Object obj = new Object();
    private volatile boolean init = false;

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        String logLevel = request.getHeader("x-log-level");
        if (logLevel != null && !logLevel.isEmpty()) {
            initLogFilter();
            MDC.put("x-log-level", logLevel.toLowerCase(Locale.ROOT));
        }
        return true;
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        MDC.remove("x-log-level");
    }

    private void initLogFilter() {
        //验证是否初始化完成
        if (init) {
            return;
        }
        synchronized (obj) {
            if (init) {
                return;
            }
            //需要先获取LoggerContext，如果有对日志做二次开发，需要想办法从其他地方获取
            LoggerContext context = LoggerContext.getContext(false);
            //配置值对应日志
            KeyValuePair tracePair = new KeyValuePair("trace", "TRACE");
            KeyValuePair debugPair = new KeyValuePair("debug", "DEBUG");
            KeyValuePair[] pairs = {tracePair, debugPair};
            DynamicThresholdFilter filter = DynamicThresholdFilter.createFilter("x-log-level", pairs, Level.INFO, Filter.Result.ACCEPT, Filter.Result.NEUTRAL);

            context.addFilter(filter);
            //更新
            context.updateLoggers();
        }
        init = true;
    }
}

上述是针对log4j2，如果项目中使用logback，基本原理一样。