THreadLocal_MDC

ThreadLocal-MDC

• 应用

  • log4j.properties

    log4j.rootLogger=info, stdout, R
    log4j.appender.stdout=org.apache.log4j.ConsoleAppender
    log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
    # Pattern to output the caller's file name and line number.
    log4j.appender.stdout.layout.ConversionPattern=%5p [%t] [%X{TRACE_ID}] (%F:%L) - %m%n
    log4j.appender.R=org.apache.log4j.RollingFileAppender
    log4j.appender.R.File=example.log
    log4j.appender.R.MaxFileSize=100KB
    # Keep one backup file
    log4j.appender.R.MaxBackupIndex=1
    log4j.appender.R.layout=org.apache.log4j.PatternLayout
    log4j.appender.R.layout.ConversionPattern=%p %t %c - %m%n
    

  • 单方法调用

    @Slf4j
    public class MDCDemo {
    
        private static final String TRACE_ID = "TRACE_ID";
    
        @Test
        public void testMdc1() {
            MDC.put(TRACE_ID, UUID.randomUUID().toString());
            log.info("log in main method");
        }
    
    }
    

    输出日志：

    INFO [main] [f6bbd26d-2620-4167-887c-993dbc529221] (MDCDemo.java:22) - log in main method

    可以看到，我们配置的TRACE_ID已经输出来了

  • 方法嵌套

    @Slf4j
    public class MDCDemo {
    
        private static final String TRACE_ID = "TRACE_ID";
    
        @Test
        public void testMdc2() {
            MDC.put(TRACE_ID, UUID.randomUUID().toString());
            log.info("log in main method");
            nestMethod();
        }
    
        private void nestMethod() {
            log.info("log in nest method");
        }
    
    }
    

    输出日志：

    INFO [main] [33cc07fc-8fdd-4f0c-9a6c-fd60cadf1f66] (MDCDemo.java:28) - log in main method
    INFO [main] [33cc07fc-8fdd-4f0c-9a6c-fd60cadf1f66] (MDCDemo.java:33) - log in nest method

    可以看到，主方法和嵌套方法里的TRACE_ID是一样的

  • 多线程调用

    @Slf4j
    public class MDCDemo {
    
        private static final String TRACE_ID = "TRACE_ID";
    
        @Test
        public void testMdc3() throws IOException {
            new Thread(() -> {
                MDC.put(TRACE_ID, UUID.randomUUID().toString());
                log.info("log in thread1 start");
                try {
                    Thread.sleep(100);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                log.info("log in thread1 end");
            }).start();
    
            new Thread(() -> {
                MDC.put(TRACE_ID, UUID.randomUUID().toString());
                log.info("log in thread2 start");
                try {
                    Thread.sleep(100);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                log.info("log in thread2 end");
            }).start();
    
            System.in.read();
        }
    
    }
    

    输出日志：

    INFO [Thread-0] [77011a2b-d5ec-4846-8a0b-0177be25464c] (MDCDemo.java:40) - log in thread1 start
    INFO [Thread-1] [ceace569-f862-41b6-97b6-0ed9561df5c3] (MDCDemo.java:51) - log in thread2 start
    INFO [Thread-0] [77011a2b-d5ec-4846-8a0b-0177be25464c] (MDCDemo.java:46) - log in thread1 end
    INFO [Thread-1] [ceace569-f862-41b6-97b6-0ed9561df5c3] (MDCDemo.java:57) - log in thread2 end

    可以看到，thread1和thread2各自的TRACE_ID互不影响