java 日志追踪MDC
MDC ( Mapped Diagnostic Contexts ) 有了日志之后，我们就可以追踪各种线上问题。
但是，在分布式系统中，各种无关日志穿行其中，导致我们可能无法直接定位整个操作流程。
因此，我们可能需要对一个用户的操作流程进行归类标记，比如使用线程+时间戳，或者用户身份标识等；如此，我们可以从大量日志信息中grep出某个用户的操作流程，或者某个时间的流转记录。其目的是为了便于我们诊断线上问题而出现的方法工具类。
虽然，Slf4j 是用来适配其他的日志具体实现包的，但是针对 MDC功能，目前只有logback 以及 log4j 支持。 MDC
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 |
package org.slf4j; import java.io.Closeable; import java.util.Map; import org.slf4j.helpers.NOPMDCAdapter; import org.slf4j.helpers.BasicMDCAdapter; import org.slf4j.helpers.Util; import org.slf4j.impl.StaticMDCBinder; import org.slf4j.spi.MDCAdapter; public class MDC { static final String NULL_MDCA_URL = "http://HdhCmsTestslf4j.org/codes.html#null_MDCA" ; static final String NO_STATIC_MDC_BINDER_URL = "http://HdhCmsTestslf4j.org/codes.html#no_static_mdc_binder" ; static MDCAdapter mdcAdapter;
public static class MDCCloseable implements Closeable { private final String key; private MDCCloseable(String key) { this .key = key; } public void close() { MDC.remove( this .key); } } private MDC() { }
static { try { mdcAdapter = StaticMDCBinder.SINGLETON.getMDCA(); } catch (NoClassDefFoundError ncde) { mdcAdapter = new NOPMDCAdapter(); String msg = ncde.getMessage(); if (msg != null && msg.indexOf( "StaticMDCBinder" ) != - 1 ) { Util.report( "Failed to load class \"org.slf4j.impl.StaticMDCBinder\"." ); Util.report( "Defaulting to no-operation MDCAdapter implementation." ); Util.report( "See " + NO_STATIC_MDC_BINDER_URL + " for further details." ); } else { throw ncde; } } catch (Exception e) { // we should never get here Util.report( "MDC binding unsuccessful." , e); } }
public static void put(String key, String val) throws IllegalArgumentException { if (key == null ) { throw new IllegalArgumentException( "key parameter cannot be null" ); } if (mdcAdapter == null ) { throw new IllegalStateException( "MDCAdapter cannot be null. See also " + NULL_MDCA_URL); } mdcAdapter.put(key, val); }
public static MDCCloseable putCloseable(String key, String val) throws IllegalArgumentException { put(key, val); return new MDCCloseable(key); }
public static String get(String key) throws IllegalArgumentException { if (key == null ) { throw new IllegalArgumentException( "key parameter cannot be null" ); }
if (mdcAdapter == null ) { throw new IllegalStateException( "MDCAdapter cannot be null. See also " + NULL_MDCA_URL); } return mdcAdapter.get(key); }
public static void remove(String key) throws IllegalArgumentException { if (key == null ) { throw new IllegalArgumentException( "key parameter cannot be null" ); }
if (mdcAdapter == null ) { throw new IllegalStateException( "MDCAdapter cannot be null. See also " + NULL_MDCA_URL); } mdcAdapter.remove(key); }
public static void clear() { if (mdcAdapter == null ) { throw new IllegalStateException( "MDCAdapter cannot be null. See also " + NULL_MDCA_URL); } mdcAdapter.clear(); }
public static Map<String, String> getCopyOfContextMap() { if (mdcAdapter == null ) { throw new IllegalStateException( "MDCAdapter cannot be null. See also " + NULL_MDCA_URL); } return mdcAdapter.getCopyOfContextMap(); }
public static void setContextMap(Map<String, String> contextMap) { if (mdcAdapter == null ) { throw new IllegalStateException( "MDCAdapter cannot be null. See also " + NULL_MDCA_URL); } mdcAdapter.setContextMap(contextMap); } public static MDCAdapter getMDCAdapter() { return mdcAdapter; } } |
简单的demo
|
1 2 3 4 5 6 7 8 9 10 11 |
package com.alibaba.otter.canal测试数据mon; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import org.slf4j.MDC; public class LogTest { private static final Logger logger = LoggerFactory.getLogger(LogTest. class ); public static void main(String[] args) { MDC.put( "THREAD_ID" , String.valueOf(Thread.currentThread().getId())); logger.info( "纯字符串信息的info级别日志" ); } } |
logback.xml 配置
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 |
< configuration scan = "true" scanPeriod = " 5 seconds" >
< jmxConfigurator /> < appender name = "STDOUT" class = "ch.qos.logback.core.ConsoleAppender" > < encoder > < pattern >%d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{56} %X{THREAD_ID} - %msg%n </ pattern > </ encoder > </ appender >
< root level = "INFO" > < appender-ref ref = "STDOUT" /> </ root > </configuration |
对应的输出日志 可以看到输出了THREAD_ID
2016-12-08 14:59:32.855 [main] INFO com.alibaba.otter.canal测试数据mon.LogTest THREAD_ID 1 - 纯字符串信息的info级别日志
slf4j只是起到适配的作用 故查看实现类LogbackMDCAdapter属性
final InheritableThreadLocal<Map<String, String>> copyOnInheritThreadLocal = new InheritableThreadLocal<Map<String, String>>();
InheritableThreadLocal 该类扩展了 ThreadLocal，为子线程提供从父线程那里继承的值：在创建子线程时，子线程会接收所有
可继承的线程局部变量的初始值，以获得父线程所具有的值。通常，子线程的值与父线程的值是一致的；但是，通过重写这个类中的 childValue 方法，子线程的值可以作为父线程值的一个任意函数。
当必须将变量（如用户 ID 和 事务 ID）中维护的每线程属性（per-thread-attribute）自动传送给创建的所有子线程时，应尽可能地采用可继承的线程局部变量，而不是采用普通的线程局部变量
验证一下
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 |
package com.alibaba.otter.canal.parse.driver.mysql; import org.junit.Test; public class TestInheritableThreadLocal { @Test public void testThreadLocal() { final ThreadLocal<String> local = new ThreadLocal<String>(); work(local); }
@Test public void testInheritableThreadLocal() { final ThreadLocal<String> local = new InheritableThreadLocal<String>(); work(local); } private void work( final ThreadLocal<String> local) { local.set( "a" ); System.out.println(Thread.currentThread() + "," + local.get()); Thread t = new Thread( new Runnable() {
@Override public void run() { System.out.println(Thread.currentThread() + "," + local.get()); local.set( "b" ); System.out.println(Thread.currentThread() + "," + local.get()); } });
t.start(); try { t.join(); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println(Thread.currentThread() + "," + local.get()); } } |
分别运行得到的输出结果
ThreadLocal 存贮输出结果
Thread[main,5,main],a
Thread[Thread-0,5,main],null
Thread[Thread-0,5,main],b
Thread[main,5,main],a
InheritableThreadLocal存贮输出结果
Thread[main,5,main],a
Thread[Thread-0,5,main],a
Thread[Thread-0,5,main],b
Thread[main,5,main],a
输出结果说明一切 对于参数传递十分有用 我知道 canal的源码中用到了MDC
在 CanalServerWithEmbedded 中的 start 和stop等方法中都有用到
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 |
public void start( final String destination) { final CanalInstance canalInstance = canalInstances.get(destination); if (!canalInstance.isStart()) { try { MDC.put( "destination" , destination); canalInstance.start(); logger.info( "start CanalInstances[{}] successfully" , destination); } finally { MDC.remove( "destination" ); } } }
public void stop(String destination) { CanalInstance canalInstance = canalInstances.remove(destination); if (canalInstance != null ) { if (canalInstance.isStart()) { try { MDC.put( "destination" , destination); canalInstance.stop(); logger.info( "stop CanalInstances[{}] successfully" , destination); } finally { MDC.remove( "destination" ); } } } } |
MDC的介绍及使用
1、MDC是什么？
MDC是（Mapped Diagnostic Context，映射调试上下文）是 log4j 和 logback 支持的一种方便在多线程条件下记录追踪日志的功能。通常打印出的日志会有线程号等信息来标志当前日志属于哪个线程，然而由于线程是可以重复使用的，所以并不能很清晰的确认一个请求的日志范围。处理这种情况一般有两种处理方式：
1）手动生成一个唯一序列号打印在日志中；
2）使用日志控件提供的MDC功能，生成一个唯一序列标记一个线程的日志；
两种方法的区别在于：
方法一只能标记一条日志，线程内其他日志需要人肉去筛选；
方法二标记整个线程的所有日志，方便grep命令查询；
对比可见，使用MDC功能更好。
2、MDC的原理
MDC 可以看成是一个与当前线程绑定的哈希表，可以往其中添加键值对。MDC 中包含的内容可以被同一线程中执行的代码所访问。当前线程的子线程会继承其父线程中的 MDC 的内容。当需要记录日志时，只需要从 MDC 中获取所需的信息即可。MDC 的内容则由程序在适当的时候保存进去。对于一个 Web 应用来说，通常是在请求被处理的最开始保存这些数据。
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 |
@RunWith (SpringRunner. class ) @SpringBootTest (classes=CreditAppApplication. class ) publicclassMDCTest{
@Test publicvoidmdcTest1(){ MDC.put( "first" , "thefirst1" );
Loggerlogger=LoggerFactory.getLogger(MDCTest. class ); MDC.put( "last" , "thelast1" );
logger.info( "checkenclosed." ); logger.debug( "themostbeautifultwowordsinenglish." );
MDC.put( "first" , "thefirst2" ); MDC.put( "last" , "thelast2" );
logger.info( "iamnotacrook." ); logger.info( "AttributedtotheformerUSpresident.17Nov1973." ); } } |
logback的配置：
3、MDC的使用
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 |
@Component @Order (Ordered.HIGHEST_PRECEDENCE) publicclassGlobalLogTagConfigextendsOncePerRequestFilter{ privatestaticfinalStringGLOBAL_LOG_TAG= "GLOG_TAG" ; privatestaticStringgenerateSeqNo(){ returnUUID.randomUUID().toString().replace( "-" , "" ).substring( 0 , 12 ); }
@Override protectedvoiddoFilterInternal(HttpServletRequesthttpServletRequest,HttpServletResponsehttpServletResponse,FilterChainfilterChain)throwsServletException,IOException{ try { StringseqNo; if (httpServletRequest!= null ){ seqNo=httpServletRequest.getHeader(GLOBAL_LOG_TAG);
if (StringUtils.isEmpty(seqNo)){ seqNo=generateSeqNo(); } } else { seqNo=generateSeqNo(); } MDC.put(GLOBAL_LOG_TAG,seqNo); filterChain.doFilter(httpServletRequest,httpServletResponse); } finally { MDC.remove(GLOBAL_LOG_TAG); } } } |
注意：
OncePerRequestFilter的作用是为了让每个请求只经过这个过滤器一次（因为web container的不同，有些过滤器可能被多次执行）
logback配置：
以上为个人经验，希望能给大家一个参考，也希望大家多多支持。
原文链接：https://HdhCmsTestjianshu测试数据/p/06b1d35526c2
查看更多关于java 如何实现日志追踪MDC的详细内容...