Traceable Logging in Spring Boot: Using Logback, Interceptors, MDC and Custom Thread Pools

The author starts by describing a common problem in large business call chains where logs from multiple services interleave, making it hard to follow a single request.

To solve this, the article proposes concatenating logs that belong to the same business call by assigning a unique TRACE_ID to each request and ensuring the ID is present in every log entry.

Project structure

The sample project includes the following key parts:

1. <dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId> <scope>test</scope> </dependency> <dependency> <groupId>org.projectlombok</groupId> <artifactId>lombok</artifactId> <version>1.16.10</version> </dependency> </dependencies> – basic Spring Boot dependencies and Lombok.

2. <?xml version="1.0" encoding="UTF-8"?> <configuration debug="false"> <property name="log" value="D:/test/log"/> <appender name="console" class="ch.qos.logback.core.ConsoleAppender"> <encoder class="ch.qos.logback.classic.encoder.PatternLayoutEncoder"> <pattern>[%X{TRACE_ID}] %d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{50} - %msg%n</pattern> </encoder> </appender> <appender name="file" class="ch.qos.logback.core.rolling.RollingFileAppender"> <rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy"> <FileNamePattern>${log}/%d{yyyy-MM-dd}.log</FileNamePattern> <MaxHistory>30</MaxHistory> </rollingPolicy> <encoder class="ch.qos.logback.classic.encoder.PatternLayoutEncoder"> <pattern>[%X{TRACE_ID}] %d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{50} - %msg%n</pattern> </encoder> <triggeringPolicy class="ch.qos.logback.core.rolling.SizeBasedTriggeringPolicy"> <MaxFileSize>10MB</MaxFileSize> </triggeringPolicy> </appender> <root level="INFO"> <appender-ref ref="console"/> <appender-ref ref="file"/> </root> </configuration> – a simple Logback configuration that prints the TRACE_ID in every log line.

3. application.yml server: port: 8826 logging: config: classpath:logback-spring.xml – sets the server port and points Spring Boot to the Logback config.

4. public class LogInterceptor implements HandlerInterceptor { private static final String TRACE_ID = "TRACE_ID"; @Override public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) { String tid = UUID.randomUUID().toString().replace("-", ""); if (!StringUtils.isEmpty(request.getHeader("TRACE_ID"))) { tid = request.getHeader("TRACE_ID"); } MDC.put(TRACE_ID, tid); return true; } @Override public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, @Nullable Exception ex) { MDC.remove(TRACE_ID); } } – a Spring MVC interceptor that generates a TRACE_ID (or reuses one from the request header) and stores it in MDC.

5. @Configuration public class WebConfigurerAdapter implements WebMvcConfigurer { @Bean public LogInterceptor logInterceptor() { return new LogInterceptor(); } @Override public void addInterceptors(InterceptorRegistry registry) { registry.addInterceptor(logInterceptor()); } } – registers the interceptor with the Spring MVC framework.

6. To handle asynchronous execution, a custom thread pool is defined:

@Configuration @EnableAsync public class ThreadPoolConfig { @Bean("MyExecutor") public Executor asyncExecutor() { MyThreadPoolTaskExecutor executor = new MyThreadPoolTaskExecutor(); executor.setCorePoolSize(5); executor.setMaxPoolSize(5); executor.setQueueCapacity(500); executor.setKeepAliveSeconds(60); executor.setThreadNamePrefix("asyncJCccc"); executor.initialize(); return executor; } }

7. public final class MyThreadPoolTaskExecutor extends ThreadPoolTaskExecutor { @Override public void execute(Runnable task) { super.execute(ThreadMdcUtil.wrap(task, MDC.getCopyOfContextMap())); } @Override public Future submit(Callable task) { return super.submit(ThreadMdcUtil.wrap(task, MDC.getCopyOfContextMap())); } @Override public Future submit(Runnable task) { return super.submit(ThreadMdcUtil.wrap(task, MDC.getCopyOfContextMap())); } } – overrides execution methods to copy the MDC context to child threads.

8. public final class ThreadMdcUtil { private static final String TRACE_ID = "TRACE_ID"; public static String generateTraceId() { return UUID.randomUUID().toString(); } public static void setTraceIdIfAbsent() { if (MDC.get(TRACE_ID) == null) { MDC.put(TRACE_ID, generateTraceId()); } } public static Callable wrap(final Callable callable, final Map context) { return () -> { if (context == null) { MDC.clear(); } else { MDC.setContextMap(context); } setTraceIdIfAbsent(); try { return callable.call(); } finally { MDC.clear(); } }; } public static Runnable wrap(final Runnable runnable, final Map context) { return () -> { if (context == null) { MDC.clear(); } else { MDC.setContextMap(context); } setTraceIdIfAbsent(); try { runnable.run(); } finally { MDC.clear(); } }; } } – utility that propagates MDC (including TRACE_ID) to asynchronous tasks.

A simple test controller is added to illustrate the effect:

@PostMapping("doTest") public String doTest(@RequestParam("name") String name) throws InterruptedException { log.info("入参 name={}", name); testTrace(); log.info("调用结束 name={}", name); return "Hello," + name; } private void testTrace() { log.info("这是一行info日志"); log.error("这是一行error日志"); testTrace2(); } private void testTrace2() { log.info("这也是一行info日志"); }

Running the application shows that each log line contains the same TRACE_ID, even when the request spawns asynchronous tasks. The author also demonstrates that without the MDC‑aware thread pool, the child thread loses the TRACE_ID, and then shows the corrected output after applying the custom executor.

Finally, the article includes a series of promotional notes and links, but the technical core provides a complete, reproducible solution for traceable logging in Spring Boot back‑end services.