Database Feed

We are in the process of making a final decision next week about which License of Lightstreamer to acquire. Meanwhile, I need to set up a proof of concept for my bosses who are flying in next week, of which the outcome of the demonstration to them will be the decision. Already, I have sent them links to the online examples, which have impressed them very much. They are still adamant that they need to see one which is set up on a demo that is closest to what we require, real time polls results sent to the client side.

From what I read on your forum, Lightstreamer say this is very possible yet they do not have an example that reads from a DB and transmits the value to the client-side on a realtime basis.

Now, my question is, can someone from Lightstreamer help me set up this even soonest possible, so that I can demonstrate this? All I need is a very simplified demo of a realtime display of poll results as they land in a DB.

Kindly help

A Data Adapter example showing a database integration will be released as soon as possible. In the meanwhile, any custom help can be obtained through the professional services offered by Lightstreamer's partner network. Please contact info@lightstreamer.com for more info on this topic.

Hi
Does the Data Adapter example with a database integration is available or not yet? We are also very interested because we need to have a proof of concept with it.
Thanks

Not yey, sorry. We have been very busy on other fronts. If anybody out there has an example to post for the community, we would be grateful.

Cheers,
Alessandro

Dear Alessandro

Is the example of a database adapter available yet. It is quite a long time since this was first mentioned and it must be a very popular request.

Regards

Gerard

Hi Gerard,

We haven't had time to work on this example yet, even if it would be pretty simple to implement.

Basically, in the case of Java, it would be enough to take the Hello-World Data Adapter and add some JDBC code to poll a DB instead of generating pseudo-random data.

Again, my call to anybody who has this example done to share it with the community.

Thanks

What are the pros and cons between

1)reading directly from a DB source
and
2)reading from a file like xml

I write a program to dynamically creates an XML file when a transaction takes place. Then feeds it to the LS. One file for each item with 6 fields.
I have about 30 items in all.

Amarin,

The best approach would be to have an asynchronous data feed (based on some message-oriented middleware), which does not require polling. Both a DB and an XML data source are usually based on polling. That said, choosing between a DB and an XML file depends on many aspects, such as the polling frequency, the amount of data being polled, general architecture considerations, including transactions and fail-over. So it's impossible to provide a general answer.

Thanks for your reply Alessandro

What would the setup look like with MOM?
Do I use it alongside lightstreamer?

Would this be ok

http://www.jboss.com/products/platforms/dataservices

or

http://www.jboss.org/projects/

Do you recommend anything else?

Thanks again

Sure, any JMS implementation would be a perfect solution.
By the way, you can find a JBoss-based example in the "Lightstreamer\DOCS-SDKs\sdk_adapter_java\examples\StockListDemo_JMS_D ataAdapter" folder of your Lightstreamer distribution.

Hi there,

I have to make a decision as to whether we can use Lightstreamer for a new project. Is there prospect of sample code for database integration being provided to developers in the near future.

Regards

Gerard

I modified the HelloWorldDataAdapter to poll a database, instead of generating the data internally.

Please consider this is just a five-minute effort and I've not tried to compile the code. Please let me know if you find any errors.

This Data Adapter uses JDBC to query an Access file ("C:/Data.mdb"). Every second, it reads the first record, extracts the "message" and "timestamp" fields and injects them into the Lightstreamer Kernel.

import java.util.*;<br /> import java.io.File;<br /> import java.sql.*;<br /> import com.lightstreamer.interfaces.data.*;<br /> <br /> public class HelloWorldDataAdapter implements SmartDataProvider {<br /> <br /> private ItemEventListener listener;<br /> private volatile GreetingsThread gt;<br /> private Statement command;<br /> <br /> public void init(Map params, File configDir) throws DataProviderException {<br /> try {<br /> Class.forName("sun.jdbc.odbc.JdbcOdbcDriver").newI nstance();<br /> String dbFile = "C:/Data.mdb";<br /> String database = "jdbc:odbc:Driver={Microsoft Access Driver (*.mdb)};DBQ="<br /> + dbFile.trim()+ ";DriverID=22;READONLY=true}";<br /> Connection conn = DriverManager.getConnection(database, "", "");<br /> command = conn.createStatement();<br /> } catch (Exception ex) {<br /> System.out.println(ex);<br /> throw new DataProviderException(ex.getMessage());<br /> }<br /> }<br /> <br /> public boolean isSnapshotAvailable(String itemName) throws SubscriptionException {<br /> return false;<br /> }<br /> <br /> public void setListener(ItemEventListener listener) {<br /> this.listener = listener;<br /> }<br /> <br /> public void subscribe(String itemName, Object itemHandle, boolean needsIterator)<br /> throws SubscriptionException, FailureException {<br /> if (itemName.equals("greetings")) {<br /> gt = new GreetingsThread(itemHandle);<br /> gt.start();<br /> }<br /> }<br /> <br /> public void subscribe(String itemName, boolean needsIterator)<br /> throws SubscriptionException, FailureException {<br /> } <br /> <br /> public void unsubscribe(String itemName) throws SubscriptionException,<br /> FailureException {<br /> if (itemName.equals("greetings") && gt != null) {<br /> gt.go = false;<br /> }<br /> }<br /> <br /> class GreetingsThread extends Thread {<br /> <br /> private final Object itemHandle;<br /> public volatile boolean go = true;<br /> <br /> public GreetingsThread(Object itemHandle) {<br /> this.itemHandle = itemHandle;<br /> }<br /> <br /> public void run() {<br /> int c = 0;<br /> Random rand = new Random();<br /> while(go) {<br /> try {<br /> ResultSet rs = command.executeQuery("select * from Data");<br /> if (rs.next()) {<br /> Map<String, String> data = new HashMap<String, String>();<br /> data.put("message", rs.getString("message"));<br /> data.put("timestamp", rs.getString("timestamp"));<br /> listener.smartUpdate(itemHandle, data, false);<br /> }<br /> } catch (Exception ex) {<br /> System.out.println(ex);<br /> } <br /> <br /> try {<br /> Thread.sleep(1000);<br /> } catch (InterruptedException e) {<br /> }<br /> }<br /> }<br /> }<br /> <br /> }

Dear Alessandro, thank you for the code. I have two questions. I don't see in the code why it just reads the "first record" - isn't it looping over the entire record set and sending them all. Secondly, if the value of a field hasn't changed since the last time it was sent to Lightstreamer, does this field value still get sent to the client.

Many thanks

Gerard

Quote:

---

Originally Posted by gerard

I don't see in the code why it just reads the "first record" - isn't it looping over the entire record set and sending them all.

---

Because in this example we suppose that the first record maps a subscribed item. So, each change in this record is pushed to the clients. In real-world scenarios, you could have different mappings.

Quote:

---

Originally Posted by gerard

Secondly, if the value of a field hasn't changed since the last time it was sent to Lightstreamer, does this field value still get sent to the client.

---

The Lightstreamer Server will take care of sending the clients only the changed values. So if no fields have changed, the Server will automatically avoid sending messages to the clients.

Cheers
Alessandro

hi Alessandro when I compile the jdbc adapter code above i get the exception - symbol : constructor DataProviderException(java.lang.Exception)
location: class com.lightstreamer.interfaces.data.DataProviderExce ption
throw new DataProviderException(ex);
1 error

Sorry, you are right; there is probably a typo, because only a DataProviderException constructor that takes a String object is available.
Please use ex.getMessage(). We'll fix the above code.

A new updated example is available at http://www.lightstreamer.com/vb/show...=3899#post3899