在生产环境下出现bug，都需要靠日志才能定位到问题的关键，而有效的日志往往能让你事半功倍。在生产并发访问情况下，日志纵横交错，那么如何快速找到你要看的日志呢？
    本章将介绍通过AOP使打印的每一条日志增加一个与业务相关的logId。

pom

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<dependency>
	<groupId>org.aspectj</groupId>
	<artifactId>aspectjweaver</artifactId>
	<version>1.7.4</version>
</dependency>

AOP环绕增强controller

    getUnique();没有给出具体实现，大家可以根据自己的业务需求，选择一个合适的值，比如用户id，流水号，都行。

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package club.usql.core.aop;

import club.usql.core.enums.ResponseEnum;
import club.usql.core.facade.domain.vo.ResponseVO;
import org.apache.commons.lang3.StringUtils;
import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.core.annotation.Order;
import org.springframework.stereotype.Component;
import org.springframework.web.context.request.RequestContextHolder;
import org.springframework.web.context.request.ServletRequestAttributes;

import javax.servlet.http.HttpServletRequest;

/**
 * @author far.liu
 */
@Aspect
@Component
@Order(0)
public class ApiLogAspect {

    private static final Logger logger = LoggerFactory.getLogger(ApiLogAspect.class);

    @Around("execution(public * club.usql..controller.*.*(..))")
    public Object aroundApi(ProceedingJoinPoint pjp) throws Throwable {
        String uri = StringUtils.EMPTY;
        try {
            Object[] args = pjp.getArgs();
            HttpServletRequest request = getRequestObj();
            uri = request.getRequestURI();

            String unique = getUnique(args);// not implemented, user_id or seq_no
            ThreadContext.put("unique", unique);

            printRequest(uri, args);
            Object result = pjp.proceed(args);
            printResponse(uri, result);
            return result;
        } catch (Exception e) {
            logger.error(e.getMessage(), e);
            ResponseVO responseVO = new ResponseVO(ResponseEnum.UNAUTHORIZED);
            printResponse(uri, responseVO);
            return responseVO;
        } finally {
            // don't forget it
            ThreadContext.clearAll();
        }
    }

    private HttpServletRequest getRequestObj() {
        return ((ServletRequestAttributes) RequestContextHolder.getRequestAttributes()).getRequest();
    }

    private void printRequest(String uri, Object[] args) {
        logger.info(String.format("call uri:%s begin, reqParam:%s", uri, args.toString()));
    }

    private void printResponse(String uri, Object args) {
        logger.info(String.format("call uri:%s end, respParam:%s", uri, args.toString()));
    }
}

log4j2.xml

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<configuration>
    <Properties>
        <Property name="LOG_HOME">e:/logs</Property>
    </Properties>
    <appenders>
        <Console name="Console" target="SYSTEM_OUT">
            <PatternLayout pattern="%d %-5p [%t] [unique:%X{unique}] %C (%F:%L) %m%n" />
        </Console>
	</appenders>
	
	 <loggers>

        <root level="DEBUG">
            <appender-ref ref="Console" />
        </root>
    </loggers>
</configuration>

效果

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2018-08-06 17:05:39,456 INFO  [thread-495] [unique:101660] club.usql.core.aop.ApiLogAspect(ApiLogAspect.java:56) call uri:/usql/test begin, reqParam:
2018-08-06 17:05:39,457 INFO  [thread-495] [unique:101660] club.usql.core.aop.ApiLogAspect(ApiLogAspect.java:56) call uri:/usql/test end, respParam:

总结

    以上代码，能让你在本此请求中，所有打印的日志，会显示你设置的unique，你可以通过这个值获取到关于本次请求的日志，不用担心在并发的情况下要根据可能重复的线程号去定位。

彩蛋

less usql.log
  1. G -> 跳转到日志结尾
  2. g -> 跳转到日志开始
  3. /interest -> 从当前位置往下搜索interest
  4. ?interest -> 从当前位置往上搜索interest
tailf usql.log

    监听日志文件，有更新立即输出

grep interest -a5b5 usql.log >> test.log

    将usql.log中的interes上下5行，输出到test.log 中，grep不适用与已经压缩的日志文件，可以使用以下命令

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gzip -dc usql.log.gz | grep interest