1、長輪詢
一句話來概括:長輪詢就是客戶端和服務器端保持連接,相互發信息。
2、流程
- 前端發出一個請求。
- 後端接收到請求後,觸發on_message方法(執行write_message("hello"))。
- 前端收到“hello”觸發on_message方法(執行渲染,把hello渲染到頁面上)。
- 後端開始輪詢,向前端發消息。
- 前端接收到信息後不斷渲染新的內容。
3、代碼示例
3.1 handler
利用PeriodicCallback進行輪詢操作。 PeriodicCallback構造函數可以接收2個參數,一個是回調的函數,一個是間隔的時間。
class LastWeekTotalCarsHandler(WebSocketHandler):
def init(self):
self.last = time.time()
self.stop = False
def check_time(self):
if time.time() - self.last > 10:
today_total = get_last_week_total_cars(0)
last_week_total = get_last_week_total_cars(-7)
last_month_total = get_last_week_total_cars(-30)
self.write_message(",".join([str(today_total), str(last_week_total), str(last_month_total)]))
self.last = time.time()
def open(self):
"""
:return:
"""
print("wedsocket opened")
self.init()
# PeriodicCallback構造函數可以接收2個參數,一個是回調的函數,一個是間隔的時間
self.timer_loop = tornado.ioloop.PeriodicCallback(self.check_time,5000)
self.timer_loop.start()
def on_message(self, message):
print("on message")
today_total = get_last_week_total_cars(0)
last_week_total = get_last_week_total_cars(-7)
last_month_total = get_last_week_total_cars(-30)
self.write_message(",".join([str(today_total), str(last_week_total), str(last_month_total)]))
self.last = time.time()
def close(self, code=None, reason=None):
self.timer_loop.stop()
3.2前端
JavaScript:
<script type="text/javascript">
var ws = new WebSocket("ws://127.0.0.1:8000/total_cars/");
ws.onopen = function () {
ws.send("Hello, world");
};
ws.onmessage = function (evt) {
var today_total = document.getElementById("todaytotal");
var last7total = document.getElementById("last7total");
var last30total = document.getElementById("last30total");
var arr = evt.data.split(",");
today_total.innerHTML = arr[0];
last7total.innerHTML =arr[1];
last30total.innerHTML = arr[2];
};
</script>
HTML:
<!-- ECharts -->
<div class="container">
<!-- <div class="col-md-2"></div>-->
<div class="col-md-9">
<div id="zqhistogram" style="width: 600px;height:400px;"></div>
</div>
<div class="col-md-1" style="text-align: center;color: rgb(71,200,211)">
<h5>今天總過車量</h5>
<h2 id="todaytotal"></h2>
</div>
<div class="col-md-1" style="text-align: center;color: rgb(71,200,211)">
<h5>近7天總過車量</h5>
<h2 id="last7total"></h2>
</div>
<div class="col-md-1" style="text-align: center;color: rgb(71,200,211)">
<h5>近30天總過車量</h5>
<h2 id="last30total"></h2>
</div>
</div>
4 展示