ajax session过期问题的几个解决方案

; //http.setRequestHeader("Content-Type","gb2312");
    this.setRequestHeader = function(mime){
        if(!this.checkHttpRequest()){
            return false;
        }
        try{
            this.HttpRequest.setRequestHeader("Content-Type", mime);
            return true;
        }catch(e){
            if(e instanceof Error){
                Alert("修改MIME类别错误");
                return false;
            }
        }
    }

    //设置状态改变的事件触发器
    this.setOnReadyStateChange = function(funHandle, Param){
        if(!this.checkHttpRequest()){
            return false;
        }
        this.ProcessRequestFunction = funHandle;
        this.ProcessRequestParam = Param;
        return true;
    }

    this.setLoadingImg = function(ImgID){
        this.LoadingImg = ImgID;
    }

    //建立HTTP连接
    //open("method","URL"[,asyncFlag[,"userName"[, "password"]]])
    this.Open = function(method, url, async, username, psw){
        if(!this.checkHttpRequest()){
            return false;
        }
        this.openMethod = method;
        this.openURL = url;
        this.openAsync = async;
        if((this.openMethod==null) || ((this.openMethod.toUpperCase()!="GET")&&(this.openMethod.toUpperCase()!="POST")&&(this.openMethod.toUpperCase()!="HEAD"))){
            Alert("请指定HTTP请求的方法，为Get、Post 或者Head");
            return false;