springmvc中requestcontextholder获取请求信息

requestcontextholder的作用是：

​ 在service层获取获取request和response信息

代码示例：

 servletrequestattributes attrs = (servletrequestattributes)requestcontextholder.getrequestattributes();
httpservletrequest request = attrs.getrequest();

源码分析：

定义了两个threadlocal变量用来存储request

 private static final threadlocal<requestattributes> requestattributesholder = new namedthreadlocal("request attributes");
    private static final threadlocal<requestattributes> inheritablerequestattributesholder = new namedinheritablethreadlocal("request context");

设置方法

    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处理servlet的类frameworkservlet的类中，doget/dopost方法，调用processrequest方法进行初始化上下文方法中initcontextholders设置进去的

 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);
        }

    }

再看一下请求信息怎么获取

    @nullable
    public static requestattributes getrequestattributes() {
        requestattributes attributes = (requestattributes)requestattributesholder.get();
        if (attributes == null) {
            attributes = (requestattributes)inheritablerequestattributesholder.get();
        }

        return attributes;
    }