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I am doing a web application using struts2 framework. After user login, I show a dashboard about the current status of the user. To show the Dashboard UI(JSP), I used to get the information from the backend (Mysql). On page loading I trigger a request eg."getDashboardInformation" (via Jquery Ajax) to get user's current dashboard information and show that information in UI.

So the request trigger only when page loads. Now I want to trigger the request whenever the user's dashboard information get updated/inserted in the mysql table (related to dashboard).

Now how could I get the dashboard information lively (eg.cricinfo - scores automatically updated in ui) without the need of refreshing the page.

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You can use Web Sockets for doing this, but be aware that Web Sockets are a new technology and in case of browser support you might have some troubles.

Web sockets are some kind of event listeners. They are awaiting events from the server like socket.onopen-event.

So you could do the following to get this done on the client side:

At first there is the function which handles the response data...

function handleResponseData(data) {
    // data could be JSON string for example
    alert(data);
}

Then you create the web socket version of handling data...

function doSocket() {
    socket = new WebSocket("ws://echo.websocket.org/");
    socket.onmessage = function(event) {
        handleResponseData(event.data);
    }
}

And then the alternative version...

function doAlternative() {
    window.setInterval(function() {
        var xmlhttp;

        if(window.XMLHttpRequest) {
            // code for IE7+, Firefox, Chrome, Opera, Safari
            xmlhttp = new XMLHttpRequest();
        }
        else {
            // code for IE6, IE5
            xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
        }

        xmlhttp.onreadystatechange=function() {
            if(xmlhttp.readyState==4 && xmlhttp.status==200 &&
                // Also check if server responded with data:
                xmlhttp.responseText)
            {
                handleResponseData(xmlhttp.responseText);
            }
        }

        xmlhttp.open("GET","echo.websocket.org",true);
        xmlhttp.send();
    }, 2000);
}

The only thing left to do is to check if web sockets are supported and to run the appropriate function...

function initialize() {
    if(typeof(WebSocket) == "function") {
        doSocket();
    }
    else {
        doAlternative();
    }
}

window.addEventListener("load", initialize, false);

With this code on the client side, you are now able to handle periodical updates. But it is important to notice that as long as you run both versions, you will need two mechanisms on the server side to handle this:

  1. A socket which periodically sends updates to the client and
  2. A servlet which handles the requests sent in the interval function.

Finally, you can get some more information about web sockets here.

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