SpringMVC中RequestContextHolder獲取請求信息

RequestContextHolder的作用是：

​ 在Service層獲取獲取request和response信息

代碼示例：

 ServletRequestAttributes attrs = (ServletRequestAttributes)RequestContextHolder.getRequestAttributes();
HttpServletRequest request = attrs.getRequest();

源碼分析：

定義了兩個ThreadLocal變量用來存儲Request

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

設置方法

    public static void setRequestAttributes(@Nullable RequestAttributes attributes) {
        setRequestAttributes(attributes, false);
    }

    public static void setRequestAttributes(@Nullable RequestAttributes attributes, boolean inheritable) {
        if (attributes == null) {
            resetRequestAttributes();
        } else if (inheritable) {
            inheritableRequestAttributesHolder.set(attributes);
            requestAttributesHolder.remove();
        } else {
            requestAttributesHolder.set(attributes);
            inheritableRequestAttributesHolder.remove();
        }

    }

是在SpringMVC處理Servlet的類FrameworkServlet的類中，doget/dopost方法，調用processRequest方法進行初始化上下文方法中initContextHolders設置進去的

 private void initContextHolders(HttpServletRequest request, @Nullable LocaleContext localeContext, @Nullable RequestAttributes requestAttributes) {
        if (localeContext != null) {
            LocaleContextHolder.setLocaleContext(localeContext, this.threadContextInheritable);
        }

        if (requestAttributes != null) {
            RequestContextHolder.setRequestAttributes(requestAttributes, this.threadContextInheritable);
        }

        if (this.logger.isTraceEnabled()) {
            this.logger.trace("Bound request context to thread: " + request);
        }

    }

再看一下請求信息怎么獲取

    @Nullable
    public static RequestAttributes getRequestAttributes() {
        RequestAttributes attributes = (RequestAttributes)requestAttributesHolder.get();
        if (attributes == null) {
            attributes = (RequestAttributes)inheritableRequestAttributesHolder.get();
        }

        return attributes;
    }