Existing LiveCycle application converting to LightStreamer

[marco.testa]

Hi

If I've well understood, what you are asking is how to implement the request reply paradigm with Lightstreamer, stated Lightstreamer is specialized for Publish/Subscribe, rather than Request/Response.
Even if there is not a direct way to implement a request/reply communication, it is possible to use Lightstreamer in a Request/reply fashion through one of the following techniques:


The first technique is to use a subscription request as an actual request for specific data, and use the first published update as the actual reply to the request.
Basically the idea is to use a disposable subscription, where the subscribed item name will represent the request.
The answer will be provided by the first (and only) published update, provided as snapshot.
Once the response is received, the client unsubscribes the given disposable item, since no other update will be published for that item.
If the response depends on the user sending the request and must be different for each user, we can leverage the getItem method of the MetadataProvired.


As example consider the case where an integer number must be summed to the user name, and the user name is a number too.
Most of the error handling is obviously missing to keep the code as small as possible.
We use the LiteralBasedProvider as base class for the MyMetadataAdapter


Client Code:


var userName = Math.round(Math.random()*100);<br /> console.log("user: " + userName);<br /> <br /> <br /> require(["LightstreamerClient","Subscription"],<br /> function(LightstreamerClient,Subscription) {<br /> <br /> var client = new LightstreamerClient("http://localhost:8080","MY_ADAPTERS");<br /> client.connectionDetails.setUser(userName);<br /> client.connect();<br /> <br /> var requestSubscription = new Subscription("MERGE","REQ:42",["response"]);<br /> requestSubscription.setRequestedSnapshot("yes");<br /> requestSubscription.addListener({<br /> onItemUpdate: function(update) {<br /> console.log("response: " + update.getValue("response"));<br /> client.unsubscribe(requestSubscription);<br /> }<br /> });<br /> <br /> client.subscribe(requestSubscription);<br /> <br /> });<br /> <br /> <br />


Metadata Adapter Server code


public class MyMetadataAdapter extends LiteralBasedProvider {<br /> <br /> public String[] getItems(String user, String sessionID, String group)<br /> throws ItemsException {<br /> <br /> String[] split = super.getItems(user,sessionID,group);<br /> for (int i = 0; i<split.length; i++) {<br /> if (split[i].startsWith("REQ:")) {<br /> split[i] = "RESP:"+user+":"+split[i].substring(4);<br /> <br /> } else if (group.startsWith("RESP:")) {<br /> // protection from unauthorized use of user-specific items<br /> throw new ItemsException("Unexpected item name");<br /> }<br /> }<br /> return split;<br /> }<br /> }<br /> <br /> <br />

Data Adapter Server code:


public class MyDataAdapter implements SmartDataProvider {<br /> <br /> <br /> private ItemEventListener listener;<br /> <br /> <br /> @Override<br /> public void setListener(ItemEventListener listener) {<br /> this.listener = listener;<br /> }<br /> <br /> @Override<br /> public void subscribe(String itemName, Object itemHandle, boolean arg2)<br /> throws SubscriptionException, FailureException {<br /> String[] request = itemName.split(":");<br /> <br /> if (!request[0].equals("RESP")) {<br /> throw new SubscriptionException("No such item");<br /> }<br /> <br /> //in this simple example the response is the request (request[2]) + the username (request[1])<br /> //if obtaining the answer is actually a long process this code should be executed in a different thread<br /> Map<String,String> resp = new HashMap<String,String>();<br /> int sum = Integer.valueOf(request[1])+Integer.valueOf(request[2]);<br /> resp.put("response", String.valueOf(sum));<br /> <br /> this.listener.smartUpdate(itemHandle, resp, true);<br /> }<br /> [cut]<br /> }<br /> <br /> <br />


To be continued ...