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java 如何實(shí)現(xiàn)日志追蹤MDC

更新時(shí)間：2021年09月23日 09:03:16 作者：holly_wang_王小飛

這篇文章主要介紹了java 實(shí)現(xiàn)日志追蹤MDC方式，具有很好的參考價(jià)值，希望對(duì)大家有所幫助。如有錯(cuò)誤或未考慮完全的地方，望不吝賜教

java 日志追蹤MDC

MDC ( Mapped Diagnostic Contexts ) 有了日志之后，我們就可以追蹤各種線上問題。

但是，在分布式系統(tǒng)中，各種無關(guān)日志穿行其中，導(dǎo)致我們可能無法直接定位整個(gè)操作流程。

因此，我們可能需要對(duì)一個(gè)用戶的操作流程進(jìn)行歸類標(biāo)記，比如使用線程+時(shí)間戳，或者用戶身份標(biāo)識(shí)等；如此，我們可以從大量日志信息中g(shù)rep出某個(gè)用戶的操作流程，或者某個(gè)時(shí)間的流轉(zhuǎn)記錄。其目的是為了便于我們?cè)\斷線上問題而出現(xiàn)的方法工具類。

雖然，Slf4j 是用來適配其他的日志具體實(shí)現(xiàn)包的，但是針對(duì) MDC功能，目前只有l(wèi)ogback 以及 log4j 支持。 MDC

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://www.slf4j.org/codes.html#null_MDCA";
    static final String NO_STATIC_MDC_BINDER_URL = "http://www.slf4j.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;
    } 
}

簡(jiǎn)單的demo

package com.alibaba.otter.canal.common; 
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("純字符串信息的info級(jí)別日志");
    }
}

logback.xml 配置

<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

對(duì)應(yīng)的輸出日志可以看到輸出了THREAD_ID

2016-12-08 14:59:32.855 [main] INFO com.alibaba.otter.canal.common.LogTest THREAD_ID 1 - 純字符串信息的info級(jí)別日志

slf4j只是起到適配的作用故查看實(shí)現(xiàn)類LogbackMDCAdapter屬性

final InheritableThreadLocal<Map<String, String>> copyOnInheritThreadLocal = new InheritableThreadLocal<Map<String, String>>();

InheritableThreadLocal 該類擴(kuò)展了 ThreadLocal，為子線程提供從父線程那里繼承的值：在創(chuàng)建子線程時(shí)，子線程會(huì)接收所有

可繼承的線程局部變量的初始值，以獲得父線程所具有的值。通常，子線程的值與父線程的值是一致的；但是，通過重寫這個(gè)類中的 childValue 方法，子線程的值可以作為父線程值的一個(gè)任意函數(shù)。

當(dāng)必須將變量（如用戶 ID 和事務(wù) ID）中維護(hù)的每線程屬性（per-thread-attribute）自動(dòng)傳送給創(chuàng)建的所有子線程時(shí)，應(yīng)盡可能地采用可繼承的線程局部變量，而不是采用普通的線程局部變量

驗(yàn)證一下

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());  
    }  
}

分別運(yùn)行得到的輸出結(jié)果

ThreadLocal 存貯輸出結(jié)果
Thread[main,5,main],a
Thread[Thread-0,5,main],null
Thread[Thread-0,5,main],b
Thread[main,5,main],a
InheritableThreadLocal存貯輸出結(jié)果
Thread[main,5,main],a
Thread[Thread-0,5,main],a
Thread[Thread-0,5,main],b
Thread[main,5,main],a

輸出結(jié)果說明一切對(duì)于參數(shù)傳遞十分有用我知道 canal的源碼中用到了MDC

在 CanalServerWithEmbedded 中的 start 和stop等方法中都有用到

    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的介紹及使用

1、MDC是什么？

MDC是（Mapped Diagnostic Context，映射調(diào)試上下文）是 log4j 和 logback 支持的一種方便在多線程條件下記錄追蹤日志的功能。通常打印出的日志會(huì)有線程號(hào)等信息來標(biāo)志當(dāng)前日志屬于哪個(gè)線程，然而由于線程是可以重復(fù)使用的，所以并不能很清晰的確認(rèn)一個(gè)請(qǐng)求的日志范圍。處理這種情況一般有兩種處理方式：

1）手動(dòng)生成一個(gè)唯一序列號(hào)打印在日志中；

2）使用日志控件提供的MDC功能，生成一個(gè)唯一序列標(biāo)記一個(gè)線程的日志；

兩種方法的區(qū)別在于：

方法一只能標(biāo)記一條日志，線程內(nèi)其他日志需要人肉去篩選；

方法二標(biāo)記整個(gè)線程的所有日志，方便grep命令查詢；

對(duì)比可見，使用MDC功能更好。

2、MDC的原理

MDC 可以看成是一個(gè)與當(dāng)前線程綁定的哈希表，可以往其中添加鍵值對(duì)。MDC 中包含的內(nèi)容可以被同一線程中執(zhí)行的代碼所訪問。當(dāng)前線程的子線程會(huì)繼承其父線程中的 MDC 的內(nèi)容。當(dāng)需要記錄日志時(shí)，只需要從 MDC 中獲取所需的信息即可。MDC 的內(nèi)容則由程序在適當(dāng)?shù)臅r(shí)候保存進(jìn)去。對(duì)于一個(gè) Web 應(yīng)用來說，通常是在請(qǐng)求被處理的最開始保存這些數(shù)據(jù)。

@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

@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的作用是為了讓每個(gè)請(qǐng)求只經(jīng)過這個(gè)過濾器一次（因?yàn)閣eb container的不同，有些過濾器可能被多次執(zhí)行）

logback配置：