ThreadLocalMap 泄漏demo

对于ThreadLocalMap泄露的示例，可以考虑以下代码：

import java.lang.reflect.Field;

public class ThreadLocalLeakDemo {

    public static void main(String[] args) throws Exception {
        ThreadLocal<Object> threadLocal = new ThreadLocal<>();

        // 设置ThreadLocal的值
        threadLocal.set(new Object());

        // 获取ThreadLocal中的ThreadLocalMap
        Field threadLocalsField = Thread.class.getDeclaredField("threadLocals");
        threadLocalsField.setAccessible(true);
        Object threadLocals = threadLocalsField.get(Thread.currentThread());
        Class<?> threadLocalMapClass = Class.forName("java.lang.ThreadLocal$ThreadLocalMap");
        Field tableField = threadLocalMapClass.getDeclaredField("table");
        tableField.setAccessible(true);
        Object[] table = (Object[]) tableField.get(threadLocals);

        // 输出ThreadLocalMap的大小
        System.out.println("ThreadLocalMap size: " + (table == null ? 0 : table.length));

        // 清空ThreadLocal的值
        threadLocal.remove();

        // 输出ThreadLocalMap的大小
        System.out.println("ThreadLocalMap size after removing the value: " + (table == null ? 0 : table.length));
    }

}

在上面的示例中，我们使用了Java的反射机制来获取当前线程的ThreadLocalMap并输出其大小。在设置ThreadLocal的值后，我们可以看到ThreadLocalMap的大小为1；在清空ThreadLocal的值后，我们可以看到ThreadLocalMap的大小仍然为1。这就是ThreadLocal泄漏的原因，即使我们在代码中手动删除了ThreadLocal的值，但是对应的Entry在ThreadLocalMap中仍然存在，这就导致了内存泄漏的问题。