Потоки в Spring. Не могу разобраться с ThreadLocal

Не могу понять как это вообще работает. Использую ThreadLocal<>. Простой пример:

Secure Bean

public class SecureBean {
    public void writeSecureMessage() {
        System.out.println("Test");
    }
}

UserInfo.java

public class UserInfo {
    private String name;
    private String password;
   /* Геттеры и сеттеры */
}

SimpleSecurityManager

public class SimpleSecurityManager implements SecurityManager {
    private static ThreadLocal<UserInfo> threadLocal = new ThreadLocal<>();
    public void login(String userName, String userPassword) {
        threadLocal.set(new UserInfo(userName, userPassword));
    }
    public void logout() {
        threadLocal.set(null);
    }
    public UserInfo getLoggedOnUser() {
        return threadLocal.get();
    }
}

SecurityAdvise.java

public class SecurityAdvise implements MethodBeforeAdvice {
    private SecurityManager securityManager;
    @Override
    public void before(Method method, Object[] objects, Object o) throws Throwable {
        UserInfo user = securityManager.getLoggedOnUser();
        if (user == null) {
            System.out.println("No user auth");
            throw new SecurityException(
                    "You must be logged to attempt to invoke this method: " + method.getName()
            );
        } else if ("admin".equals(user.getName())) {
            System.out.println("Logged user is admin - OK!");
        } else {
            System.out.println("Bad user!");
            throw new SecurityException(
                    "You must be logged to attempt to invoke this method: " + method.getName()
            );
        }
    }
    public void setSecurityManager(SecurityManager securityManager) {
        this.securityManager = securityManager;
    }
}

AppConfig.java

@Configuration
public class AppConfig {
    @Bean("securityManager")
    public SecurityManager securityManager() {
        return new SimpleSecurityManager();
    }
    @Bean("securityAdvise")
    public SecurityAdvise securityAdvise() {
        SecurityAdvise advise = new SecurityAdvise();
        advise.setSecurityManager(securityManager());
        return advise;
    }
    @Bean("secureBean")
    public SecureBean secureBean() {
        SecureBean target = new SecureBean();
        SecurityAdvise advise = securityAdvise();
        ProxyFactory proxyFactory = new ProxyFactory();
        proxyFactory.setTarget(target);
        proxyFactory.addAdvice(advise);
        return (SecureBean) proxyFactory.getProxy();
    }
}

Application.java(Работает)

public class Application {
    public static void main(String[] args) {
        ApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);
        SecureBean secureBean = (SecureBean) context.getBean("secureBean");
        SecurityManager securityManager = (SecurityManager) context.getBean("securityManager");
        securityManager.login("admin", "pass");
        secureBean.writeSecureMessage();
        securityManager.logout();
    }
}

Application.java(Всё так же работает)

public class Application {
    public static void main(String[] args) {
        ApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);
        SecureBean secureBean = (SecureBean) context.getBean("secureBean");
        SecurityManager securityManager = (SecurityManager) context.getBean("securityManager");
        securityManager.login("admin", "pass");
        new ThreadLocal<UserInfo>().set(new UserInfo("Wrong username", "Another thread?"));
        secureBean.writeSecureMessage();
        securityManager.logout();
    }
}

Application.java(Опять же работает)

public class Application {
    public static void main(String[] args) {
        ApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);
        SecureBean secureBean = (SecureBean) context.getBean("secureBean");
        SecurityManager securityManager = new SecurityManager();
        securityManager.login("admin", "pass");
        secureBean.writeSecureMessage();
        securityManager.logout();
    }
}