Spring源码中的责任链设计的确实精辟!

• 📋 模式定义
• 🏗️ UML类图
• 🌟 Spring中的责任链
• 1. `FilterChain` - Servlet Filter链
• 2. `HandlerInterceptor`链 - Spring MVC拦截器
• 3. `HandlerExceptionResolver`链 - 异常处理
• 4. `Interceptor`链 - AOP通知器链
• 5. `AsyncHandlerInterceptor` - 异步拦截器链
• ⚖️ 责任链 vs 装饰器
• 练习
• 练习1：实现Filter责任链
• 练习2：Spring MVC异常处理链
• 下一步
• 参考

📋 模式定义

使多个对象都有机会处理请求，从而避免请求的发送者和接收者之间的耦合关系。将这些对象连成一条链，并沿着这条链传递该请求，直到有一个对象处理它为止。

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Spring核心应用：FilterChain、Interceptor链、HandlerExceptionResolver

🏗️ UML类图

classDiagram    class Handler {        <<interface>>        +set_next(handler) Handler        +handle(request) Response    }    class ConcreteHandlerA {        +handle(request) Response    }    class ConcreteHandlerB {        +handle(request) Response    }    Handler <|-- ConcreteHandlerA : 实现    Handler <|-- ConcreteHandlerB : 实现    ConcreteHandlerA --> Handler : next

🌟 Spring中的责任链

1. FilterChain - Servlet Filter链

// Spring Boot中的Filter链（Spring MVC）// Handler接口：FilterpublicinterfaceFilter{voidinit(FilterConfig filterConfig)throws ServletException;voiddoFilter(ServletRequest request, ServletResponse response, FilterChain chain)throws IOException, ServletException;voiddestroy();}// 具体过滤器1：编码过滤器@Component@Order(1)publicclassCharacterEncodingFilterimplementsFilter{@OverridepublicvoiddoFilter(ServletRequest request, ServletResponse response, FilterChain chain){        request.setCharacterEncoding("UTF-8");        response.setCharacterEncoding("UTF-8");        chain.doFilter(request, response);  // 传递链    }}// 具体过滤器2：安全过滤器@Component@Order(2)publicclassSecurityFilterextendsOncePerRequestFilter{@OverrideprotectedvoiddoFilterInternal(HttpServletRequest request,                                    HttpServletResponse response,                                    FilterChain filterChain){        String token = request.getHeader("Authorization");if (token == null || !validate(token)) {            response.setStatus(401);return;  // 终止链        }        filterChain.doFilter(request, response);  // 继续传递    }}// 具体过滤器3：日志过滤器@Component@Order(3)publicclassLoggingFilterimplementsFilter{@OverridepublicvoiddoFilter(ServletRequest request, ServletResponse response, FilterChain chain){long start = System.currentTimeMillis();        logger.info("Request: " + request.getRemoteAddr());        chain.doFilter(request, response);        logger.info("Cost: " + (System.currentTimeMillis() - start));    }}// FilterChain：Spring Boot自动组装// DelegatingFilterProxyRegistrationBean负责注册所有Filter// 最终通过ApplicationFilterChain链式调用

执行流程：

Request → EncodingFilter → SecurityFilter → LoggingFilter → DispatcherServlet

2. HandlerInterceptor链 - Spring MVC拦截器

// Spring MVC拦截器链：HandlerExecutionChain// Handler: HandlerInterceptor（处理器拦截器）publicinterfaceHandlerInterceptor{booleanpreHandle(HttpServletRequest request, HttpServletResponse response, Object handler)throws Exception;voidpostHandle(HttpServletRequest request, HttpServletResponse response,                    Object handler, ModelAndView modelAndView)throws Exception;voidafterCompletion(HttpServletRequest request, HttpServletResponse response,                         Object handler, Exception ex)throws Exception;}// 具体拦截器1：性能监控@ComponentpublicclassPerformanceInterceptorimplementsHandlerInterceptor{privatestaticfinal ThreadLocal<Long> startTime = new ThreadLocal<>();@OverridepublicbooleanpreHandle(HttpServletRequest request, HttpServletResponse response,                             Object handler){        startTime.set(System.currentTimeMillis());returntrue;  // 继续链    }@OverridepublicvoidafterCompletion(HttpServletRequest request, HttpServletResponse response,                                 Object handler, Exception ex){long duration = System.currentTimeMillis() - startTime.get();        logger.info("Handler {} took {} ms", handler, duration);        startTime.remove();    }}// 具体拦截器2：权限检查@ComponentpublicclassAuthInterceptorimplementsHandlerInterceptor{@OverridepublicbooleanpreHandle(HttpServletRequest request, HttpServletResponse response,                             Object handler){        User user = (User) request.getSession().getAttribute("user");if (user == null) {            response.sendRedirect("/login");returnfalse;  // 终止链        }returntrue;  // 继续链    }}// 具体拦截器3：日志记录@ComponentpublicclassAccessLogInterceptorimplementsHandlerInterceptor{@OverridepublicvoidpostHandle(HttpServletRequest request, HttpServletResponse response,                           Object handler, ModelAndView modelAndView){        logger.info("User {} accessed {}", request.getUserPrincipal(), request.getRequestURI());    }}// 配置：注册拦截器链@ConfigurationpublicclassWebMvcConfigimplementsWebMvcConfigurer{@Autowiredprivate PerformanceInterceptor perfInterceptor;@Autowiredprivate AuthInterceptor authInterceptor;@Autowiredprivate AccessLogInterceptor logInterceptor;@OverridepublicvoidaddInterceptors(InterceptorRegistry registry){        registry.addInterceptor(perfInterceptor)                .addPathPatterns("/**");        registry.addInterceptor(authInterceptor)                .addPathPatterns("/api/**")                .excludePathPatterns("/api/public/**");        registry.addInterceptor(logInterceptor)                .addPathPatterns("/**");    }}// HandlerExecutionChain：Spring内部责任链publicclassHandlerExecutionChain{privatefinal Object handler;private HandlerInterceptor[] interceptors;publicvoidapplyPreHandle(HttpServletRequest request, HttpServletResponse response){for (int i = 0; i < this.interceptors.length; i++) {            HandlerInterceptor interceptor = this.interceptors[i];if (!interceptor.preHandle(request, response, this.handler)) {// 返回false，链终止                triggerAfterCompletion(request, response, null);returnfalse;            }        }returntrue;    }publicvoidapplyPostHandle(...){// 逆序调用postHandle    }publicvoidapplyAfterCompletion(...){// 逆序调用afterCompletion    }}

执行流程：

请求 → PerformanceInterceptor.preHandle()    → AuthInterceptor.preHandle()    → Handler（Controller）    → AccessLogInterceptor.postHandle()    → PerformanceInterceptor.afterCompletion()

3. HandlerExceptionResolver链 - 异常处理

// Spring MVC异常解析器链// Handler: HandlerExceptionResolverpublicinterfaceHandlerExceptionResolver{ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response,                                    Object handler, Exception ex);}// 具体解析器1：ExceptionHandlerExceptionResolver（@ExceptionHandler）@ComponentpublicclassExceptionHandlerExceptionResolverimplementsHandlerExceptionResolver{@Overridepublic ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response,                                          Object handler, Exception ex){// 查找@ExceptionHandler方法        HandlerMethod handlerMethod = (HandlerMethod) handler;        Method method = handlerMethod.getMethod();        ExceptionHandlerMethodResolver resolver = getExceptionHandlerMethodResolverFor(method);if (resolver != null) {            Method exHandler = resolver.resolveMethod(ex);if (exHandler != null) {return invokeExceptionHandlerMethod(exHandler, ex);            }        }returnnull;  // 继续链    }}// 具体解析器2：ResponseStatusExceptionResolver（@ResponseStatus）@ComponentpublicclassResponseStatusExceptionResolverimplementsHandlerExceptionResolver{@Overridepublic ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response,                                          Object handler, Exception ex){if (ex instanceof ResponseStatusException) {            ResponseStatus status = ex.getClass().getAnnotation(ResponseStatus.class);if (status != null) {                response.setStatus(status.value().value());returnnew ModelAndView();  // 空ModelAndView表示已处理            }        }returnnull;  // 继续链    }}// 具体解析器3：DefaultHandlerExceptionResolver（默认处理）@ComponentpublicclassDefaultHandlerExceptionResolverimplementsHandlerExceptionResolver{@Overridepublic ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response,                                          Object handler, Exception ex){if (ex instanceof NoHandlerFoundException) {            response.setStatus(HttpStatus.NOT_FOUND.value());returnnew ModelAndView("error/404");        }if (ex instanceof HttpRequestMethodNotSupportedException) {            response.setStatus(HttpStatus.METHOD_NOT_ALLOWED.value());returnnew ModelAndView("error/405");        }        response.setStatus(HttpStatus.INTERNAL_SERVER_ERROR.value());returnnew ModelAndView("error/500");    }}// DispatcherServlet异常处理链// 多个HandlerExceptionResolver通过order排序// Spring按order从小到大依次尝试，第一个返回非null的处理成功

4. Interceptor链 - AOP通知器链

// AOP拦截器链：`DefaultChainedInterceptor`publicclassDefaultChainedInterceptorimplementsInterceptor{privatefinal List<MethodInterceptor> interceptors;privateint currentInterceptorIndex = -1;@Overridepublic Object invoke(MethodInvocation invocation)throws Throwable {// 创建新的Invocation链        ChainedMethodInvocation chain = new ChainedMethodInvocation(invocation, this);return chain.invokeProceed();    }privateclassChainedMethodInvocationimplementsInterceptorMethodInvocation{privatefinal MethodInvocation invocation;privatefinal DefaultChainedInterceptor chain;@Overridepublic Object proceed()throws Throwable {this.currentInterceptorIndex++;if (this.currentInterceptorIndex < interceptors.size()) {                MethodInterceptor interceptor = interceptors.get(this.currentInterceptorIndex);return interceptor.invoke(this);  // 传递到下一个拦截器            }// 链末端，调用目标方法returnthis.invocation.proceed();        }    }}// 示例：事务+日志+权限链List<MethodInterceptor> chain = Arrays.asList(new LoggingInterceptor(),      // 1. 日志new TransactionInterceptor(),  // 2. 事务new SecurityInterceptor()      // 3. 权限);// 执行顺序：// LoggingInterceptor.invoke() → 调用chain.proceed()//   ↓ TransactionInterceptor.invoke() → 调用chain.proceed()//     ↓ SecurityInterceptor.invoke() → 调用target.method()//     ↑ 返回//   ↑ 返回// ↑ 返回// ✅ 外层装饰器（日志）最先执行，内层装饰器（安全）最后执行

5. AsyncHandlerInterceptor - 异步拦截器链

// Spring WebFlux中的责任链（响应式）// Handler: WebFilter（响应式过滤器）publicinterfaceWebFilter{Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain);}// 具体过滤器@ComponentpublicclassMetricsWebFilterimplementsWebFilter{@Overridepublic Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain){long start = System.currentTimeMillis();return chain.filter(exchange)                .doFinally(signal -> {long duration = System.currentTimeMillis() - start;                    Metrics.record(exchange.getRequest().getPath(), duration);                });    }}@ComponentpublicclassSecurityWebFilterimplementsWebFilter{@Overridepublic Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain){return ServerWebExchangeUtils            .getPrincipal(exchange)            .flatMap(principal -> chain.filter(exchange))  // 继续链            .switchIfEmpty(Mono.error(new UnauthorizedException()));    }}// WebFilterChain：响应式链publicinterfaceWebFilterChain{Mono<Void> filter(ServerWebExchange exchange);}// 使用：链式组合（响应式）List<WebFilter> filters = Arrays.asList(new MetricsWebFilter(),new SecurityWebFilter(),new LoggingWebFilter());// 组装成链WebFilterChain chain = exchange -> {if (index >= filters.size()) {return handler.handle(exchange);  // 到达Handler    }return filters.get(index++).filter(exchange, chain);};

⚖️ 责任链 vs 装饰器

Spring中两者的统一： AOP拦截器链既是责任链（每个决定是否继续），也是装饰器（层层包装）。 但责任链可以中途停止（返回false），装饰器必须最终调用目标。

练习

练习1：实现Filter责任链

// 模拟Spring Filter链publicinterfaceMyFilter{voiddoFilter(HttpServletRequest request, HttpServletResponse response, FilterChain chain);}publicinterfaceFilterChain{voiddoFilter(HttpServletRequest request, HttpServletResponse response);}publicclassBasicFilterChainimplementsFilterChain{privatefinal List<MyFilter> filters;privateint index = 0;publicBasicFilterChain(List<MyFilter> filters, HttpServletRequest req, HttpServletResponse res){this.filters = filters;this.request = req;this.response = res;    }@OverridepublicvoiddoFilter(HttpServletRequest request, HttpServletResponse response){if (index >= filters.size()) {// 链末端，执行目标            target.handle(request, response);return;        }// 当前过滤器        MyFilter filter = filters.get(index++);        filter.doFilter(request, response, this);    }}

练习2：Spring MVC异常处理链

// 实现简化的HandlerExceptionResolver链publicclassSimpleExceptionResolverChain{privatefinal List<HandlerExceptionResolver> resolvers;public ModelAndView resolve(HttpServletRequest request, HttpServletResponse response,                                 Object handler, Exception ex){for (HandlerExceptionResolver resolver : resolvers) {            ModelAndView mav = resolver.resolveException(request, response, handler, ex);if (mav != null) {return mav;  // 第一个处理的生效            }        }returnnull;  // 无人处理    }}

下一步

✅ 掌握责任链模式后，继续学习：

👉 命令模式

参考

• 🌐 Spring Framework - HandlerInterceptor

• 🌐 Spring Framework - HandlerExceptionResolver

• 🌐 Spring Framework - Filter