TraceId 使用

## MDC注入和打印

简单示例
```
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.slf4j.MDC;
import java.util.UUID;

public class SimpleMDC {

private static final Logger logger = LoggerFactory.getLogger(SimpleMDC.class);
    public static final String REQ_ID = "REQ_ID";

public static void main(String[] args) {
        MDC.put(REQ_ID, UUID.randomUUID().toString());
        logger.info("开始调用服务A，进行业务处理");
        logger.info("业务处理完毕，可以释放空间了，避免内存泄露");
        MDC.remove(REQ_ID);
        logger.info("REQ_ID 还有吗？{}", MDC.get(REQ_ID) != null);
    }
}
```
配置 logback.xml，通过 %X{REQ_ID} 来打印 REQ_ID 的信息
```
<?xml version="1.0" encoding="UTF-8" ?>
<configuration>
    <appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
        <layout class="ch.qos.logback.classic.PatternLayout">
            <Pattern>[%t] [%X{REQ_ID}] - %m%n</Pattern>
        </layout>
    </appender>
    <root level="debug">
        <appender-ref ref="CONSOLE"/>
    </root>
</configuration>
```
POM依赖
```
<dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-api</artifactId>
        <version>1.7.7</version>
    </dependency>
    <dependency>
        <groupId>ch.qos.logback</groupId>
        <artifactId>logback-core</artifactId>
        <version>1.2.3</version>
    </dependency>
    <dependency>
        <groupId>ch.qos.logback</groupId>
        <artifactId>logback-access</artifactId>
        <version>1.2.3</version>
    </dependency>
    <dependency>
        <groupId>ch.qos.logback</groupId>
        <artifactId>logback-classic</artifactId>
        <version>1.2.3</version>
    </dependency>
```

参考：https://www.cnblogs.com/socoool/p/12742503.html