ajax session过期问题的几个解决方案

;                       }
                        break;
                    }catch(e){
                        //alert(i);
                        http = false;
                    }
                }
            }else if(window.XMLHttpRequest){
                http = new XMLHttpRequest();
                if(http.overrideMimeType){
                    http.overrideMimeType("text/xml");
                }
            }
        }catch(e){
            http = false;
        }

        if(!http){
            Alert("不能创建XMLHttpRequest对象实例");
            return http;
        }

        this.HttpRequest = http;
        return http;
    }

    //检测 this.HttpRequest
    this.checkHttpRequest = function(){
        if(!this.HttpRequest){
            return this.InitHttpRequest();
        }
        return this.HttpRequest;
    }

    //修改MIME类别
    //http.setRequestHeader("Content-Type", "application/x-www-form-urlencoded"); //如果要传文件或者Post 内容给服务器
    //http.setRequestHeader("Content-Type","text/xml");