How to get MDC logging working for Spring Batch

Question

In Spring Batch it would be great to keep track of the execution thread through logging. However, MDC does not seem to work.

MDC.put("process", "batchJob"); logger.info("{}; status={}", getJobName(), batchStatus.name());

Anyone got MDC working in Spring Batch?

Answer 1

I solved it by adding a JobExecutionListener like that:

public class Slf4jBatchJobListener implements JobExecutionListener {

    private static final String DEFAULT_MDC_UUID_TOKEN_KEY = "Slf4jMDCFilter.UUID";
    private final Logger logger = LoggerFactory.getLogger(getClass());

    public void beforeJob(JobExecution jobExecution) {
        String token = UUID.randomUUID().toString().toUpperCase();
        MDC.put(DEFAULT_MDC_UUID_TOKEN_KEY, token);
        logger.info("Job {} with id {} starting...", jobExecution.getJobInstance().getJobName(), jobExecution.getId());
    }

    public void afterJob(JobExecution jobExecution) {
        logger.info("Job {} with id {} ended.", jobExecution.getJobInstance().getJobName(), jobExecution.getId());
        MDC.remove(DEFAULT_MDC_UUID_TOKEN_KEY);
    }
}

Because some jobs are multi-threaded, I had to add also a TaskDecorator in order to copy the DMC from the parent thread to the subthread like this:

public class Slf4JTaskDecorator implements TaskDecorator {

    @Override
    public Runnable decorate(Runnable runnable) {
        Map<String, String> contextMap = MDC.getCopyOfContextMap();
        return () -> {
            try {
                MDC.setContextMap(contextMap);
                runnable.run();
            } finally {
                MDC.clear();
            }
        };
    }
}

Set the TaskDecorator to the TaskExecutor:

@Bean
public TaskExecutor taskExecutor(){
    SimpleAsyncTaskExecutor taskExecutor = new SimpleAsyncTaskExecutor("spring_batch");
    taskExecutor.setConcurrencyLimit(maxThreads);
    taskExecutor.setTaskDecorator(new Slf4JTaskDecorator());
    return taskExecutor;
}

And lastly, update the logging pattern in properties:

logging:
  pattern:
    level: "%5p %X{Slf4jMDCFilter.UUID}"