Spring TaskDecorator that propagates an SLF4J MDC to the runner's thread. Accounts for the possibility that the runner's thread is actually the same as the caller's thread by restoring the old MDC context, if existing.

MDCPropagatingTaskDecorator.java

import org.slf4j.MDC;
import org.springframework.core.task.TaskDecorator;

import java.util.Map;

public class MDCPropagatingTaskDecorator implements TaskDecorator {

    @Override
    public Runnable decorate(Runnable runnable) {
        Map<String, String> callerContext = MDC.getCopyOfContextMap();
        if (callerContext == null) return runnable;
        return () -> {
            Map<String, String> executorContext = MDC.getCopyOfContextMap();
            try {
                MDC.setContextMap(callerContext);
                runnable.run();
            } finally {
                MDC.clear();
                if (executorContext != null) {
                    // intended for the case that we're running in the caller's thread
                    MDC.setContextMap(executorContext);
                }
            }
        };
    }
}