bhaktimehta's Blog

Server Sent Events Sample with Glassfish

Introduction

Server-Sent Events (SSE) is a standard describing how servers can initiate data transmission towards clients once an initial client connection has been established.
It is commonly used to send message updates or continuous data streams to a browser client and designed to enhance native, cross-browser streaming through a JavaScript API called EventSource, through which a client requests a particular URL in order to receive an event stream.

Sample

The sample demonstrates a simple example of SSE. Here we have a servlet which periodically polls for Twitter information and pushes the data to the clients using Server Sent Events. This samples showcases a JavaEE6 application that uses CDI,ServerSentEventHandler and ServerSentEventHandlerContext apis along with twitter search apis and javascript client code. 

Code Snippets

Here is the code for the ServletContextInitializer. There is a Timer which gets the feeds periodically

public class SSEServletContextListener implements ServletContextListener {

    @Inject
    TwitterFeedBean tfs;

    private final int time = 60;

    @Override
    public void contextInitialized(ServletContextEvent servletContextEvent) {
        ServletContext servletContext = servletContextEvent.getServletContext();
        try{
            // create the timer and timer task objects
            Timer timer = new Timer();

            TwitterTimerTask task = new TwitterTimerTask(tfs);

            timer.schedule(task, 0, 1000 * time);

            // save our timer for later use
            servletContext.setAttribute ("timer", timer);
        } catch (Exception e) {
            servletContext.log ("Problem initializing timer task every "+ time +" seconds: "
                    + e.getMessage ());
        }
    }

    @Override
    public void contextDestroyed(ServletContextEvent servletContextEvent) {
        ServletContext servletContext = servletContextEvent.getServletContext();

        Timer timer = (Timer)servletContext.getAttribute ("timer");

        if (timer != null)
            timer.cancel();

        servletContext.removeAttribute ("timer");
    }

    class TwitterTimerTask extends TimerTask {
        TwitterFeedBean bean;
        TwitterTimerTask(TwitterFeedBean  t)   {
            this.bean = t;
        }

        public void run() {
            try {
                bean.getFeeds();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

Here is the TwitterHandler which is a ServerSentEventHandler

/**
 * TwitterHandler class which will send messages using Server Sent Events
 * 
 * @author Bhakti Mehta
 */
@ServerSentEvent("/twittersse")
public class TwitterHandler extends ServerSentEventHandler {


    @Override
    public void onConnected(ServerSentEventConnection client) {
        super.onConnected(client);

    }

    public void sendMessage(String data) {
        System.out.println("Handler="+this+" Sending data="+data);
        try {
            connection.sendMessage(data);
        } catch(IOException ioe) {
            // May be client is already disconnected. Just close it
            try {
                connection.close();
            } catch(Exception e) {
                //ignore if the connection close threw an exception
            }
        }

    }

@Named
@ApplicationScoped
public class TwitterFeedBean {

    @Inject @ServerSentEventContext("/twittersse")
    ServerSentEventHandlerContext<TwitterHandler> sc;


    final private String SEARCH_URL =
            "http://search.twitter.com/search.json?q=glassfish&rpp=5&include_entities=true" +
                    "&with_twitter_user_id=true&result_type=mixed";


    public TwitterFeedBean() {
    }

    public void getFeeds() throws IOException {

        for(TwitterHandler handler : sc.getHandlers()) {
            handler.sendMessage(composeMessage());
        }

    }

    private  String composeMessage() {
        return getFeedData();
    }

    private  String getFeedData() {
        StringBuilder sb = new StringBuilder();
        try {
            URL twitter = new URL(SEARCH_URL);
            URLConnection yc = null;

            yc = twitter.openConnection();


            BufferedReader in = new BufferedReader(
                    new InputStreamReader(
                            yc.getInputStream()));
            String inputLine;

            while ((inputLine = in.readLine()) != null) {
                System.out.println("Input line" + inputLine);
                sb.append(inputLine)  ;

            }
            in.close();

            return sb.toString();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return new String("Error in getting data from the feeds ") ;
    }



}

Finally here is the app.js which will create the EventSource. It also parses the JSON feeds

var network = function (eventSource) {
    return {
        initialize: function() {
            var url = 'http://' + document.location.host
                + '/sse-twitter-sample/twittersse';
            eventSource = new EventSource(url);


            eventSource.onmessage = function (event) {
                var feeds = event.data.toString();
                console.log(feeds);
                var theNewParagraph = document.createElement('p');

                var theBreak = document.createElement('br');
                theNewParagraph.setAttribute('title','The feeds');
                var data = JSON.parse(feeds);
                var theText;

                var divTag ;
                var tweetInfo  ;

                // Before we continue we check that we got data
                if(data !== undefined) {
                    for (var k = 0;k<5;k++) {
                        tweetInfo = data.results[k];


                        divTag = document.createElement("div");
                        divTag.id = "div"+k;
                        divTag.setAttribute("align","left");
                        divTag.style.margin = "0px auto";
                        divTag.className ="outerDiv";


                        divTag.innerHTML =
                            '<a href="https://twitter.com/#!/search/%23glassfish'+'">'+ tweetInfo.text+'<\/a>'+

                                 ' Created on '  + tweetInfo.created_at  ;


                        document.body.appendChild(divTag);
                        document.body.appendChild(theBreak);

                    }


                }
                  document.body.appendChild(theNewParagraph);

            };
        },
        send: function(commandn) {
            eventSource.send(command);
        }
    }
};

var APP = {
    network: network(null),

    initialize: function () {
        APP.network.initialize();
    }
};

window.onload = APP.initialize;

Quick tip Felix shell and Glassfish

Here is a pointer to a blog which shows how to use the felix shell with Glassfish 3.2 to inspect dependencies.

mod_jk and EJB Webservices and Glassfish 3.1

One of the nice bug fixes we added in v3.1 was support for mod_jk with ejb webservices issue 12458.

Amy has a very nice blog on setting up mod_jk here

Download Glassfish v3.1 from here and try it out and give us feedback at users@glassfish.dev.java.net

Update to deploying webservices on Glassfish 3.1 cluster

This blog is a minor update to the previous entry of www.java.net/blog/bhaktimehta/archive/2010/07/23/deploying-webservices-glassfish-31-cluster

Glassfish 3.1 is in active development and there are some changes since the last time I posted this blog.

Most of the steps remain same and I am using the same setup on 2 machines.

Steps

1. Install Glassfish 3.1 b23 from http://dlc.sun.com.edgesuite.net/glassfish/3.1/promoted/latest-glassfish.zip

2. DAS is my mac and other instance is on adc2180404

3. asadmin start-domain

Waiting for the server to start ..........
Successfully started the domain : domain1
domain  Location: /Users/bhakti/b23/glassfishv3/glassfish/domains/domain1
Log File: /Users/bhakti/b23/glassfishv3/glassfish/domains/domain1/logs/server.log
Admin Port: 4848
Debugging is enabled.  The debugging port is: 9009
Command start-domain executed successfully.

4.asadmin create-cluster mycluster

Command create-cluster executed successfully.

5.asadmin create-node-config --nodehost adc2180404.us.oracle.com adcconf
Command create-node-config executed successfully.

6.Additional step (You need to specify the installdir param )

asadmin update-node-config --installdir
/scratch/bhamehta/b23/glassfishv3/glassfish adcconf

Command update-node-config executed successfully.

7.asadmin create-instance --cluster mycluster --node adcconf mycluster_i1

The instance mycluster_i1 was registered with the DAS.  You must run the following comand on the instance host to complete the instance creation:
 asadmin  --host bhakti-mehtas-macbook-pro.local --port 4848 create-local-instance --node adcconf mycluster_i1

Command create-instance executed successfully.

(On adc2180404)

8.asadmin  --host dhcp-santaclara22-1fl-west-10-132-178-100.usdhcp.oraclecorp.com --port 4848 create-local-instance --node adcconf mycluster_i1
Rendezvoused with DAS on dhcp-santaclara22-1fl-west-10-132-178-100.usdhcp.oraclecorp.com:4848.
Command create-local-instance executed successfully.

9.asadmin start-local-instance mycluster_i1

Waiting for the server to start ............
Successfully started the instance: mycluster_i1
instance Location: /scratch/bhamehta/b23/glassfishv3/glassfish/nodes/adcconf/mycluster_i1
Log File: /scratch/bhamehta/b23/glassfishv3/glassfish/nodes/adcconf/mycluster_i1/logs/server.log
Admin Port: 24849
Command start-local-instance executed successfully.

On Das

./asadmin deploy --target mycluster /Users/bhakti/ejbwsinwar/dist/ejbwsinwar.war

I tried deploying the war which we developed as part of this blog

http://weblogs.java.net/blog/bhaktimehta/archive/2010/06/24/ejb-webservi... and could access the wsdl from the instance.