spring通过RequestContextHolder获取HttpServletRequest对象

1.获取HttpServletRequest对象方法：

    public static HttpServletRequest getRequest() {ServletRequestAttributes attributes = ((ServletRequestAttributes) RequestContextHolder.getRequestAttributes());assert attributes != null;return attributes.getRequest();}

2.RequestContextHolder是一个持有请求和响应上下文的对象，其持有如下两个ThreadLocal对象用于保存当前请求的上下文对象

    private static final ThreadLocal<RequestAttributes> requestAttributesHolder = new NamedThreadLocal("Request attributes");private static final ThreadLocal<RequestAttributes> inheritableRequestAttributesHolder = new NamedInheritableThreadLocal("Request context");

RequestContextHolder类中全部是静态方法，可以直接使用设置属性、清空属性相关方法；

3.RequestContextFilter过滤器用户设置和销毁当前上下文对象

public class RequestContextFilter extends OncePerRequestFilter {...protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain) throws ServletException, IOException {ServletRequestAttributes attributes = new ServletRequestAttributes(request, response);//初始化this.initContextHolders(request, attributes);try {filterChain.doFilter(request, response);} finally {//销毁this.resetContextHolders();if (this.logger.isTraceEnabled()) {this.logger.trace("Cleared thread-bound request context: " + request);}attributes.requestCompleted();}}private void initContextHolders(HttpServletRequest request, ServletRequestAttributes requestAttributes) {LocaleContextHolder.setLocale(request.getLocale(), this.threadContextInheritable);//初始化上下文属性RequestContextHolder.setRequestAttributes(requestAttributes, this.threadContextInheritable);if (this.logger.isTraceEnabled()) {this.logger.trace("Bound request context to thread: " + request);}}private void resetContextHolders() {LocaleContextHolder.resetLocaleContext();//销毁上下文属性RequestContextHolder.resetRequestAttributes();}
}

4.RequestContextFilter过滤器对象实例化

• RequestContextFilter对象有一个子类OrderedRequestContextFilter

public class OrderedRequestContextFilter extends RequestContextFilter implements OrderedFilter {private int order = -105;public OrderedRequestContextFilter() {}public int getOrder() {return this.order;}public void setOrder(int order) {this.order = order;}
}

• RequestContextFilter过滤器的实例化实际上是通过OrderedRequestContextFilter对象实例化实现

OrderedRequestContextFilter过滤器源码：

public class OrderedRequestContextFilter extends RequestContextFilter implements OrderedFilter {//过滤器执行优先级  private int order = -105;public OrderedRequestContextFilter() {}public int getOrder() {return this.order;}public void setOrder(int order) {this.order = order;}
}

OrderedRequestContextFilter过滤器实例化：

		@Bean@ConditionalOnMissingBean({ RequestContextListener.class, RequestContextFilter.class })@ConditionalOnMissingFilterBean(RequestContextFilter.class)public static RequestContextFilter requestContextFilter() {return new OrderedRequestContextFilter();}

org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration.WebMvcAutoConfigurationAdapter#requestContextFilter

5.OncePerRequestFilter过滤器

OncePerRequestFilter是Spring框架中一个抽象类，用于确保过滤器在每次请求中只通过一次，这是通过重写doFilterInternal方法来实现的，而不是通过重写doFilter方法。OncePerRequestFilter通过Spring的过滤器链管理来确保这一点。

6.RequestContextFilter在整个servlet容器中的顺序

• CharacterEncodingFilter -2147483648
• WebStaFilterRegistrationBean -2147483647
• FormContentFilter -9900
• RequestContextFilter(OrderedRequestContextFilter) -105

过滤器的顺序排序是在org.springframework.boot.web.servlet.ServletContextInitializerBeans#ServletContextInitializerBeans中进行：

    @SafeVarargspublic ServletContextInitializerBeans(ListableBeanFactory beanFactory, Class<? extends ServletContextInitializer>... initializerTypes) {this.initializerTypes = initializerTypes.length != 0 ? Arrays.asList(initializerTypes) : Collections.singletonList(ServletContextInitializer.class);this.addServletContextInitializerBeans(beanFactory);this.addAdaptableBeans(beanFactory);//对过滤器进行排序this.sortedList = this.initializers.values().stream().flatMap((value) -> {return value.stream().sorted(AnnotationAwareOrderComparator.INSTANCE);}).toList();this.logMappings(this.initializers);}

开源 SDK：https://github.com/mingyang66/spring-parent