错误日志的实时抓取保证代码质量
背景介绍：公司使用的网络容器是tomcat，引入了log4j，研发的代码中记录了详细的日志。所有的网页行为包括后套的job定时任务等，都会把日志按定义的级别写入tomcat/log/catalina.out文件中。那么监控该文件，就能捕获可视页面无法感知到的错误。
Linux下使用命令：
tail -f catalina.out |grep -C 36 ERROR该命令实时读取日志文件，把出现“ERROR”行的日志前后各36日志打印出来。
也可以把日志记录到文本中：
tail -f catalina.out |grep -C 36 ERROR >>error.log下面是改命令捕获的一个错误日志，在页面上测试时候，没有弹出任何错误提示：
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:230)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at com.mk.security.SSOFilter.doFilter(SSOFilter.java:221)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:108)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:108)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:522)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:620)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:349)
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:1110)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:785)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1425)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)
2017-02-07 16:45:14.183 [catalina-exec-80] INFO com.mk.shop.service.ShopService - selectTradeStatisticsMapcom.mk.vo.StatisticsItemVo@3427a14c[date=02-06,ymddate=<null>,num=0,rate=0,ratestr=<null>,uv=0]
2017-02-07 16:45:14.189 [catalina-exec-80] INFO com.mk.shop.service.ShopService - selectTradeStatisticsMapcom.mk.vo.StatisticsItemVo@363f3a3a[date=02-05,ymddate=<null>,num=0,rate=0,ratestr=<null>,uv=0]
2017-02-07 16:45:14.196 [catalina-exec-80] INFO com.mk.shop.service.ShopService - selectTradeStatisticsMapcom.mk.vo.StatisticsItemVo@719b7a9e[date=02-04,ymddate=<null>,num=0,rate=0,ratestr=<null>,uv=0]
2017-02-07 16:45:14.201 [catalina-exec-80] INFO com.mk.shop.service.ShopService - selectTradeStatisticsMapcom.mk.vo.StatisticsItemVo@c80b0d6[date=02-03,ymddate=<null>,num=0,rate=0,ratestr=<null>,uv=0]
2017-02-07 16:45:14.207 [catalina-exec-80] INFO com.mk.shop.service.ShopService - selectTradeStatisticsMapcom.mk.vo.StatisticsItemVo@706dab29[date=02-02,ymddate=<null>,num=0,rate=0,ratestr=<null>,uv=0]
2017-02-07 16:45:14.212 [catalina-exec-80] INFO com.mk.shop.service.ShopService - selectTradeStatisticsMapcom.mk.vo.StatisticsItemVo@6161143e[date=02-01,ymddate=<null>,num=0,rate=0,ratestr=<null>,uv=0]
2017-02-07 16:45:14.219 [catalina-exec-80] ERROR c.m.b.controller.ExceptionResolver - java.lang.NullPointerException
at com.mk.shop.service.ShopService.lambda$selectTradeStatisticsMap$4(ShopService.java:241)
at java.util.TimSort.countRunAndMakeAscending(TimSort.java:355)
at java.util.TimSort.sort(TimSort.java:220)
at java.util.Arrays.sort(Arrays.java:1512)
at java.util.ArrayList.sort(ArrayList.java:1454)
at java.util.Collections.sort(Collections.java:175)
at com.mk.shop.service.ShopService.selectTradeStatisticsMap(ShopService.java:241)
at com.mk.shop.service.ShopService$$FastClassBySpringCGLIB$$99569971.invoke(<generated>)
at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:711)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157)
at org.springframework.aop.aspectj.MethodInvocationProceedingJoinPoint.proceed(MethodInvocationProceedingJoinPoint.java:85)
at com.mk.web.aspect.CacheAspect.doArround(CacheAspect.java:61)
at sun.reflect.GeneratedMethodAccessor442.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethodWithGivenArgs(AbstractAspectJAdvice.java:621)
at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethod(AbstractAspectJAdvice.java:610)
at org.springframework.aop.aspectj.AspectJAroundAdvice.invoke(AspectJAroundAdvice.java:68)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:98)
at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:262)
at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:95)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:644)
at com.mk.shop.service.ShopService$$EnhancerBySpringCGLIB$$6790a1c6.selectTradeStatisticsMap(<generated>)
at com.mk.shop.controller.ShopController.selectTradeStatisticsMap(ShopController.java:161)
at com.mk.shop.controller.ShopController$$FastClassBySpringCGLIB$$8bbcf00f.invoke(<generated>)
at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:711)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157)
at org.springframework.aop.framework.adapter.MethodBeforeAdviceInterceptor.invoke(MethodBeforeAdviceInterceptor.java:52)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92)找到日志，提供给开发同学，那么他自然就知道错误是怎么来的。
这个，是研发开发中，调试代码跟踪日志，自然而然发展出来追踪错误的一种办法。对于不懂代码或者对代码一知半解的测试来说，是发现错误一个不错的选择。
