public class SecurityContextHolder {
	// ~ Static fields/initializers
	// =====================================================================================

	public static final String MODE_THREADLOCAL = "MODE_THREADLOCAL";
	public static final String MODE_INHERITABLETHREADLOCAL = "MODE_INHERITABLETHREADLOCAL";
	public static final String MODE_GLOBAL = "MODE_GLOBAL";
	public static final String SYSTEM_PROPERTY = "spring.security.strategy";
	private static String strategyName = System.getProperty(SYSTEM_PROPERTY);
	private static SecurityContextHolderStrategy strategy;
	private static int initializeCount = 0;

	private static void initialize() {
		if (!StringUtils.hasText(strategyName)) {
			// 如果沒有設(shè)置自定義的策略，就采用MODE_THREADLOCAL模式
			strategyName = MODE_THREADLOCAL;
		}
			// ThreadLocal策略
		if (strategyName.equals(MODE_THREADLOCAL)) {
			strategy = new ThreadLocalSecurityContextHolderStrategy();
		}
		// 采用InheritableThreadLocal，它是ThreadLocal的一個(gè)子類
		else if (strategyName.equals(MODE_INHERITABLETHREADLOCAL)) {
			strategy = new InheritableThreadLocalSecurityContextHolderStrategy();
		}
		// 全局策略，實(shí)現(xiàn)方式就是static SecurityContext contextHolder
		else if (strategyName.equals(MODE_GLOBAL)) {
			strategy = new GlobalSecurityContextHolderStrategy();
		}
		else {
			// Try to load a custom strategy  自定義的策略，通過返回創(chuàng)建出
			try {
				Class<?> clazz = Class.forName(strategyName);
				Constructor<?> customStrategy = clazz.getConstructor();
				strategy = (SecurityContextHolderStrategy) customStrategy.newInstance();
			}
			catch (Exception ex) {
				ReflectionUtils.handleReflectionException(ex);
			}
		}

		initializeCount++;
	}

final class ThreadLocalSecurityContextHolderStrategy implements
		SecurityContextHolderStrategy {
	// ~ Static fields/initializers
	// =====================================================================================

	private static final ThreadLocal<SecurityContext> contextHolder = new ThreadLocal<>();
	。。。。。。
}

final class InheritableThreadLocalSecurityContextHolderStrategy implements
		SecurityContextHolderStrategy {
	// ~ Static fields/initializers
	// =====================================================================================

	private static final ThreadLocal<SecurityContext> contextHolder = new InheritableThreadLocal<>();
	。。。。。。
}

final class GlobalSecurityContextHolderStrategy implements SecurityContextHolderStrategy {
	// ~ Static fields/initializers
	// =====================================================================================

	private static SecurityContext contextHolder;
	。。。。。。
}