在SpringBoot项目中添加logback的MDC

先看下MDC是什么

Mapped Diagnostic Context，用于打LOG时跟踪一个“会话“、一个”事务“。举例，有一个web controller，在同一时间可能收到来自多个客户端的请求，如果一个请求发生了错误，我们要跟踪这个请求从controller开始一步步都执行到了哪些代码、有哪些log的输出。这时我们可以看log文件，但是log文件是多个请求同时记录的，基本无法分辨哪行是哪个请求产生的，虽然我们可以看线程，但线程可能被复用，也是很难分辨出，这时MDC就派上用场了。

我们可以加一个web filter，在请求进来时，把”标识“放到MDC context中，比如：put( ip, 8.8.8.8), put(username, 'yang')，在filter结束时把context再清掉，即可在整个请求处理过程中，都可以打印出ip, username这些数据，就可以方便的用于日志跟踪。

在SpringBoot中怎么用

1. 写一个LogInterceptor，用于统一处理MDC:

@Component
public class LogInterceptor implements HandlerInterceptor {
private final static String REQUEST_ID = "requestId";
private static final Logger LOGGER = LoggerFactory.getLogger(LogInterceptor.class);
@Override
public boolean preHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o) throws Exception {
String xForwardedForHeader = httpServletRequest.getHeader("X-Forwarded-For");
String remoteIp = httpServletRequest.getRemoteAddr();
String uuid = UUID.randomUUID().toString();
LOGGER.info("put requestId ({}) to logger", uuid);
LOGGER.info("request id:{}, client ip:{}, X-Forwarded-For:{}", uuid, remoteIp, xForwardedForHeader);
MDC.put(REQUEST_ID, uuid);
return true;
}
@Override
public void postHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, ModelAndView modelAndView) throws Exception {
String uuid = MDC.get(REQUEST_ID);
LOGGER.info("remove requestId ({}) from logger", uuid);
MDC.remove(REQUEST_ID);
}
@Override
public void afterCompletion(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, Exception e) throws Exception {
}
}

关键代码在于：MDC.put(REQUEST_ID, uuid);

2. 注册一下这个Interceptor，写一个WebMvcConfigurer类：

@Configuration
public class WebMvcConfigurer extends WebMvcConfigurerAdapter {
@Autowired
private LogInterceptor logInterceptor;
@Override
public void addInterceptors(InterceptorRegistry registry) {
registry.addInterceptor(logInterceptor);
super.addInterceptors(registry);
}
}

3. 放一个logback.xml到src/main/resources/目录中，用于配置logback的参数，如没有，请新建一个

<configuration scan="true" scanPeriod="30 seconds" debug="true">
<appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
<target>System.out</target>
<encoder>
<pattern>[%date{ISO8601}] [%-5level] - [%thread] [%X{requestId}] [%logger] [%X{akkaSource}] - %msg %rootException %n
</pattern>
</encoder>
</appender>
<root level="INFO">
<appender-ref ref="STDOUT"/>
</root>
</configuration>

注意这个<pattern/>中配置了输出 requestId

4. 最后看下效果，下面加粗的即为requestId

[2017-12-14 16:08:45,677] [INFO ] - [http-nio-8080-exec-1] [a08f86cd-6743-48ce-816a-f5ee61b802b8]