深入理解Log4j2 ThreadContext的线程上下文继承机制与高级应用

-Dlog4j2.isThreadContextMapInheritable=true
-DisThreadContextMapInheritable=true  (旧版本兼容)

import org.apache.logging.log4j.ThreadContext;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

public class ThreadContextInheritanceDemo {

    private static final Logger logger = LogManager.getLogger(ThreadContextInheritanceDemo.class);

    public static void main(String[] args) throws InterruptedException {
        // 确保JVM参数设置 -Dlog4j2.isThreadContextMapInheritable=true

        // 1. 父线程设置初始值
        ThreadContext.put("traceId", "INITIAL_VALUE");
        logger.info("Parent Thread - Initial traceId: {}", ThreadContext.get("traceId"));

        Thread childThread = new Thread(() -> {
            logger.info("Child Thread - TraceId upon creation: {}", ThreadContext.get("traceId")); // 此时应为 INITIAL_VALUE

            // 2. 子线程尝试更新自己的ThreadContext
            ThreadContext.put("traceId", "CHILD_UPDATED_VALUE");
            logger.info("Child Thread - TraceId after update: {}", ThreadContext.get("traceId"));

            try {
                Thread.sleep(100); // 确保父线程有时间更新
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            }
            logger.info("Child Thread - Final traceId: {}", ThreadContext.get("traceId")); // 仍为 CHILD_UPDATED_VALUE
        });

        childThread.start();

        // 3. 父线程在子线程启动后更新ThreadContext
        ThreadContext.put("traceId", "PARENT_UPDATED_VALUE");
        logger.info("Parent Thread - TraceId after update: {}", ThreadContext.get("traceId")); // 此时应为 PARENT_UPDATED_VALUE

        childThread.join(); // 等待子线程结束
        logger.info("Parent Thread - Final traceId: {}", ThreadContext.get("traceId")); // 仍为 PARENT_UPDATED_VALUE
    }
}

// 1. 定义一个全局共享的上下文数据管理器
public class GlobalLogContext {
    private static final ThreadLocal<Map<String, String>> currentContext =
            InheritableThreadLocal.withInitial(HashMap::new); // 示例，实际可能更复杂

    public static void put(String key, String value) {
        currentContext.get().put(key, value);
    }

    public static Map<String, String> getContextMap() {
        return new HashMap<>(currentContext.get()); // 返回副本以防止外部修改
    }

    public static void clear() {
        currentContext.remove();
    }
}

// 2. 实现 ContextDataProvider
import org.apache.logging.log4j.core.util.ContextDataProvider;
import java.util.Map;

public class CustomGlobalContextDataProvider implements ContextDataProvider {

    @Override
    public Map<String, String> getContextData() {
        // 从自定义的全局管理器中获取数据
        return GlobalLogContext.getContextMap();
    }
}

// 3. 在 META-INF/services/org.apache.logging.log4j.core.util.ContextDataProvider 文件中添加：
// com.yourpackage.CustomGlobalContextDataProvider