public enum AuthorizationInterceptorsOrder {
	FIRST(Integer.MIN_VALUE),
	/**
	 * {@link PreFilterAuthorizationMethodInterceptor}
	 */
	PRE_FILTER,
	PRE_AUTHORIZE,
	SECURED,
	JSR250,
	POST_AUTHORIZE,
	/**
	 * {@link PostFilterAuthorizationMethodInterceptor}
	 */
	POST_FILTER,
	LAST(Integer.MAX_VALUE);
	...
}

@Configuration
// 其中prepostEnabled默認true,其他注解配置默認false,需手動改為true
@EnableMethodSecurity(securedEnabled = true)
@RequiredArgsConstructor
public class SecurityConfig {
	// 白名單
	private static final String[] AUTH_WHITELIST = ... 
    @Bean
    public SecurityFilterChain securityFilterChain(HttpSecurity http) throws Exception {
	    // antMatcher or mvcMatcher
        http.authorizeHttpRequests()
                .antMatchers(AUTH_WHITELIST).permitAll()
                // hasRole中不需要添加 ROLE_前綴
                // ant 匹配 /admin /admin/a /admin/a/b 都會匹配上
                .antMatchers("/admin/**").hasRole("ADMIN")
                .anyRequest().authenticated();
                // denyAll慎用
//                .anyRequest().denyAll();
//        http.authorizeHttpRequests()
//                .mvcMatchers(AUTH_WHITELIST).permitAll()
//                        // 效果同上
//                        .mvcMatchers("/admin").hasRole("ADMIN")
//                        .anyRequest().denyAll();
    }
}

@Api("user")
@RestController
@RequestMapping("/user")
@RequiredArgsConstructor
public class UserController {
	/**
     * {@link EnableMethodSecurity} 注解必須配置在配置類上<br/>
     * {@link PreAuthorize}等注解中表達式使用 Spring EL
     * @return
     */
    @PreAuthorize("hasRole('ADMIN')")
    @GetMapping("/admin")
    public ResponseEntity<Map<String, Object>> admin() {
        return ResponseEntity.ok(Collections.singletonMap("msg","u r admin"));
    }
}

public class AuthorizationFilter extends OncePerRequestFilter {
	// 在配置類中默認實現(xiàn)為 RequestMatcherDelegatingAuthorizationManager
	private final AuthorizationManager<HttpServletRequest> authorizationManager;
		@Override
	protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
			throws ServletException, IOException {
		// 委托給AuthorizationManager
		AuthorizationDecision decision = this.authorizationManager.check(this::getAuthentication, request);
		if (decision != null && !decision.isGranted()) {
			throw new AccessDeniedException("Access Denied");
		}
		filterChain.doFilter(request, response);
	}
}

public final class RequestMatcherDelegatingAuthorizationManager implements AuthorizationManager<HttpServletRequest> {
	// http.authorizeHttpRequests().antMatchers(AUTH_WHITELIST)...
	// SecurityFilterChain中每配置一項就會增加一個Entry
	// RequestMatcherEntry包含一個RequestMatcher和一個待鑒權(quán)對象，這里是AuthorizationManager
	private final List<RequestMatcherEntry<AuthorizationManager<RequestAuthorizationContext>>> mappings;
	...
	@Override
	public AuthorizationDecision check(Supplier<Authentication> authentication, HttpServletRequest request) {
		for (RequestMatcherEntry<AuthorizationManager<RequestAuthorizationContext>> mapping : this.mappings) {
			RequestMatcher matcher = mapping.getRequestMatcher();
			MatchResult matchResult = matcher.matcher(request);
			if (matchResult.isMatch()) {
				AuthorizationManager<RequestAuthorizationContext> manager = mapping.getEntry();
				return manager.check(authentication,
						new RequestAuthorizationContext(request, matchResult.getVariables()));
			}
		}
		return null;
	}
}

@Configuration(proxyBeanMethods = false)
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
final class PrePostMethodSecurityConfiguration {
	private final AuthorizationManagerBeforeMethodInterceptor preAuthorizeAuthorizationMethodInterceptor;
	private final PreAuthorizeAuthorizationManager preAuthorizeAuthorizationManager = new PreAuthorizeAuthorizationManager();
	private final DefaultMethodSecurityExpressionHandler expressionHandler = new DefaultMethodSecurityExpressionHandler();
	...
	@Autowired
	PrePostMethodSecurityConfiguration(ApplicationContext context) {
		// 設置 Spring EL 解析器
		this.preAuthorizeAuthorizationManager.setExpressionHandler(this.expressionHandler);	
		// 攔截@PreAuthorize方法
		this.preAuthorizeAuthorizationMethodInterceptor = AuthorizationManagerBeforeMethodInterceptor
				.preAuthorize(this.preAuthorizeAuthorizationManager);
		...
	}
	...
}

public final class AuthorizationManagerBeforeMethodInterceptor
		implements Ordered, MethodInterceptor, PointcutAdvisor, AopInfrastructureBean {
	/**
	 * 調(diào)用起點
	 */
	public static AuthorizationManagerBeforeMethodInterceptor preAuthorize() {		
		// 針對 @PreAuthorize注解提供的AuthorizationManager為PreAuthorizeAuthorizationManager
		return preAuthorize(new PreAuthorizeAuthorizationManager());
	}
	/**
	 * 初始化，創(chuàng)建基于@PreAuthorize注解的aop方法攔截器
	 * Creates an interceptor for the {@link PreAuthorize} annotation
	 * @param authorizationManager the {@link PreAuthorizeAuthorizationManager} to use
	 * @return the interceptor
	 */
	public static AuthorizationManagerBeforeMethodInterceptor preAuthorize(
			PreAuthorizeAuthorizationManager authorizationManager) {
		AuthorizationManagerBeforeMethodInterceptor interceptor = new AuthorizationManagerBeforeMethodInterceptor(
				AuthorizationMethodPointcuts.forAnnotations(PreAuthorize.class), authorizationManager);
		interceptor.setOrder(AuthorizationInterceptorsOrder.PRE_AUTHORIZE.getOrder());
		return interceptor;
	}
	...	
	// 實現(xiàn)MethodInterceptor方法，在調(diào)用實際方法是會首先觸發(fā)這個
	@Override
	public Object invoke(MethodInvocation mi) throws Throwable {
		// 先鑒權(quán)
		attemptAuthorization(mi);
		// 后執(zhí)行實際方法
		return mi.proceed();
	}
	private void attemptAuthorization(MethodInvocation mi) {
		// 判斷, @PreAuthorize方法用的manager就是
		// PreAuthorizeAuthorizationManager
		// 是通過上面的static類構(gòu)造的
		AuthorizationDecision decision = this.authorizationManager.check(AUTHENTICATION_SUPPLIER, mi);
		if (decision != null && !decision.isGranted()) {
			throw new AccessDeniedException("Access Denied");
		}
		...
	}
	static final Supplier<Authentication> AUTHENTICATION_SUPPLIER = () -> {
		Authentication authentication = SecurityContextHolder.getContext().getAuthentication();
		if (authentication == null) {
			throw new AuthenticationCredentialsNotFoundException(
					"An Authentication object was not found in the SecurityContext");
		}
		return authentication;
	};
}

public final class PreAuthorizeAuthorizationManager implements AuthorizationManager<MethodInvocation> {
	private final PreAuthorizeExpressionAttributeRegistry registry = new PreAuthorizeExpressionAttributeRegistry();
	private MethodSecurityExpressionHandler expressionHandler = new DefaultMethodSecurityExpressionHandler();
	@Override
	public AuthorizationDecision check(Supplier<Authentication> authentication, MethodInvocation mi) {
		// 獲取方法上@PreAuthorize注解中的Spring EL 表達式屬性
		ExpressionAttribute attribute = this.registry.getAttribute(mi);
		if (attribute == ExpressionAttribute.NULL_ATTRIBUTE) {
			return null;
		}
		// Spring EL 的 context
		EvaluationContext ctx = this.expressionHandler.createEvaluationContext(authentication.get(), mi);
		// 執(zhí)行表達式中結(jié)果, 會執(zhí)行SecurityExpressionRoot類中對應方法。涉及Spring EL執(zhí)行原理，pass
		boolean granted = ExpressionUtils.evaluateAsBoolean(attribute.getExpression(), ctx);	
		// 返回結(jié)果
		return new ExpressionAttributeAuthorizationDecision(granted, attribute);
	}
}