Long Polling in AJAX using php
Question
I am using AJAX for refreshing some part of the page using AJAX, so that i don't have to reload the page again & again.
But i want the table to refresh only when there is a change ( long polling ). But i am not getting how to do that. I have tried using for loops with break statement but i am not getting the proper logic i guess.
The files are as follows
getuser.php
<!DOCTYPE html>
<html>
<head>
<style>
table {
width: 100%;
border-collapse: collapse;
}
table, td, th {
border: 1px solid black;
padding: 5px;
}
th {text-align: left;}
</style>
</head>
<body>
<?php
$conn = mysqli_connect('localhost','root','','bondplus');
if (!$conn) {
die('Could not connect: ' . mysqli_error($con));
}
mysqli_select_db($conn,"bondplus");
$sql="SELECT * FROM `user_details`";
$result = mysqli_query($conn,$sql);
echo "<table>
<tr>
<th>Firstname</th>
<th>Mobile</th>
<th>Email</th>
<th>Type</th>
<th>Hometown</th>
</tr>";
while($row = mysqli_fetch_array($result)) {
echo "<tr>";
echo "<td>" . $row['u_name'] . "</td>";
echo "<td>" . $row['mob'] . "</td>";
echo "<td>" . $row['email'] . "</td>";
echo "<td>" . $row['type'] . "</td>";
echo "<td>" . $row['address'] . "</td>";
echo "</tr>";
}
echo "</table>";
mysqli_close($conn);
?>
</body>
</html>
trefresh.php
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<title>AJAX Example</title>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<script type="text/javascript" src="reloader.js"></script>
</head>
<body onload="reloadData()">
<p> HELLO There!</p>
<div id="currentData" align="center">
<p>Loading Data...</p>
</div>
</body>
<script>
var req;
function reloadData()
{
var now = new Date();
url = 'getuser.php?' + now.getTime();
try {
req = new XMLHttpRequest();
} catch (e) {
try {
req = new ActiveXObject("Msxml2.XMLHTTP");
} catch (e) {
try {
req = new ActiveXObject("Microsoft.XMLHTTP");
} catch (oc) {
alert("No AJAX Support");
return;
}
}
}
req.onreadystatechange = processReqChange;
req.open("GET", url, true);
req.send(null);
}
function processReqChange()
{
// If req shows "complete"
if (req.readyState == 4)
{
dataDiv = document.getElementById('currentData');
// If "OK"
if (req.status == 200)
{
// Set current data text
dataDiv.innerHTML = req.responseText;
// Start new timer (1 min)
timeoutID = setTimeout('reloadData()', 6000);
}
else
{
// Flag error
dataDiv.innerHTML = '<p>There was a problem retrieving data: ' + req.statusText + '</p>';
}
}
}
</script>
</html>
2 answers
solution1
0 2016-02-11 12:44:49
Check for the if(req.status == 304) in your code which represents no modification in the response. If not 304 then you can update the table.
solution2
0 2016-02-11 13:07:24
First, I would like to give you 2 important advices :
Answer :
back-end : Create an EventLayer in your project
It will receive a signal from another entity that something new was happened, for example: you can use ActiveMQ OR it will send a request each N seconds to an external entity to check if there is something new ( you can store flag in memcache or in synchronized Data Source Server like ANYEM ), and after that flush data (data creation will be, of course created by a business layer)
front-end pretty simple, you will loop on your own Ajax, example
function ajaxLongPollingManager() {
$.ajax({
url: "yourproject.event.php"
}).done(function(response) {
// do your job ....
// ...
// and loop back
ajaxLongPollingManager();
}).fail(function(response) {
// manage/handle your errors
// ...
// and loop back
ajaxLongPollingManager();
});
}
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